Patent Publication Number: US-2013230425-A1

Title: Two-step zinc phosphating process

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/530,519, filed Sep. 2, 2011, which is incorporated by reference herein in its entirety. 
    
    
     FIELD 
     The present invention relates to methods for treating a multi-metal assembly comprising a first portion comprising an aluminum substrate and a second portion comprising a non-aluminum metal substrate. 
     BACKGROUND 
     For a variety of reasons, such as a desire to improve fuel economy, some automobile manufacturers are using increasing amounts of aluminum in the construction of their vehicles. As a result, multi-metal assemblies that include a greater amount of aluminum substrate in combination with non-aluminum, such as steel, substrates, may become more common. 
     Pretreating metal substrates, including aluminum and steel substrates, with phosphate conversion coatings has been conventional for promoting corrosion resistance. One disadvantage with the conventional phosphating of multi-metal substrates, however, is that for every square meter of aluminum processed, 0.5 to 5 grams of aluminum is etched off of the substrate. Moreover, for every gram of aluminum etched off the substrate, a significant amount of cryolite (Na 3 AlF 6 ) sludge is formed. In addition, as aluminum content increases, downstream filtration systems can be overwhelmed, resulting in dusty/gritty layers of horizontal surfaces which translate into poor appearance of subsequently applied coating layers. 
     As a result, it is desirable to provide improved processes for treatment of multi-metal assemblies that address at least some of the problems associated with conventional phosphating treatments and yet still promote good corrosion resistance performance. 
     SUMMARY OF THE INVENTION 
     In some respects, the present invention is directed to methods for treating a multi-metal assembly comprising: (i) a first portion comprising an aluminum substrate and (ii) a second portion comprising a non-aluminum metal substrate. These methods comprise: (a) treating the multi-metal assembly by contacting the assembly with a zinc-phosphate composition comprising: (1) phosphate ions; (2) zinc ions; (3) free fluoride; and (4) a Group IIIB and/or IVB metal; and (b) contacting the treated multi-metal assembly with a composition comprising: (1) fluorozirconic acid; and (2) a second source of fluoride ions. 
     In other respects, the present invention is directed to methods for treating a multi-metal assembly comprising: (i) a first portion comprising an aluminum substrate and (ii) a second portion comprising a non-aluminum metal substrate. These methods comprise: (a) treating the multi-metal assembly by contacting the assembly with a zinc-phosphate composition comprising: (1) phosphate ions; (2) zinc ions; (3) free fluoride; and (4) a Group IIIB and/or IVB metal comprising zirconium, wherein a ratio of the moles per liter of free fluoride in the zinc-phosphate composition to the square root of the moles per liter of zirconium in the zinc-phosphate composition is greater than 10; and (b) contacting the treated multi-metal assembly with a composition comprising: (1) a Group IIIB and/or IVB metal, and (2) free fluoride. 
     In still other respects, the present invention is directed to methods for treating a multi-metal assembly comprising: (i) a first portion comprising an aluminum alloy substrate, wherein the aluminum alloy comprises at least 0.25% by weight copper, and (ii) a second portion comprising a non-aluminum metal substrate. These methods comprise: (a) treating the multi-metal assembly by contacting the assembly with a zinc-phosphate composition comprising: (1) phosphate ions; (2) zinc ions; (3) free fluoride; and (4) a Group IIIB and/or IVB metal; and (b) contacting the treated multi-metal assembly with a composition comprising: (1) a Group IIIB and/or IVB metal, and (2) free fluoride. 
     The present invention is also directed to, among other things, related treated substrates. 
    
    
     DETAILED DESCRIPTION 
     For purposes of the following detailed description, it is to be understood that the invention may assume various alternative variations and step sequences, except where expressly specified to the contrary. Moreover, other than in any operating examples, or where otherwise indicated, all numbers expressing, for example, quantities of ingredients used in the specification and claims are to be understood as being modified in all instances by the term “about”. Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. 
     Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard variation found in their respective testing measurements. 
     Also, it should be understood that any numerical range recited herein is intended to include all sub-ranges subsumed therein. For example, a range of “1 to 10” is intended to include all sub-ranges between (and including) the recited minimum value of 1 and the recited maximum value of 10, that is, having a minimum value equal to or greater than 1 and a maximum value of equal to or less than 10. 
     In this application, the use of the singular includes the plural and plural encompasses singular, unless specifically stated otherwise. In addition, in this application, the use of “or” means “and/or” unless specifically stated otherwise, even though “and/or” may be explicitly used in certain instances. 
     As indicated earlier, certain embodiments of the present invention are directed to methods for treating a multi-metal assembly comprising: (i) a first portion comprising an aluminum substrate and (ii) a second portion comprising a non-aluminum metal substrate. 
     As used herein, the term “aluminum substrate” refers to substrate constructed of a material that is predominantly (&gt;50% by weight) aluminum. Suitable aluminum substrates include, for example, aluminum itself, aluminum alloys, aluminum plated steel and aluminum alloy plated steel. In certain embodiments, the aluminum substrate comprises 10 to 90 percent of the total surface area of the multi-metal assembly. Exemplary aluminum substrates that are suitable for use in the multi-metal assembly treated in the present invention are aluminum alloys, such as the 1000, 2000, 3000, 4000, 5000, 6000 and 7000 series aluminum alloys, such as aluminum alloy 6022, 6016, and 6111. Indeed, the methods of the present invention have been found to be particularly beneficial when an aluminum alloy having a relatively high copper content (as used herein, “relatively high copper content” means the aluminum alloy comprises at least 0.25% by weight copper, such as at least 0.50% by weight copper) is used as part of the multi-metal assembly. In certain embodiments, therefore, the multi-metal substrate comprises a first portion comprising an aluminum alloy substrate having a copper content of at least 0.25% by weight, in some cases, at least 0.50% by weight, such as is the case with aluminum alloy 6111 which, as will be appreciated by those skilled in the art, has a composition comprising, by weight: 95.6 to 98.3% Al, no more than 0.10% Cr, 0.50 to 0.90% Cu, no more than 0.40% Fe, 0.5 to 1.0% Mg, 0.10 to 0.45% Mn, 0.60 to 1.10% Si, no more than 0.10% Ti, and no more than 0.15% Zn. 
     As used herein, the term “non-aluminum metal substrate” refers to metal substrates that are not “aluminum substrates” as defined above. Suitable non-aluminum metal substrates include, but are not limited to, substrates constructed of cold rolled steel, hot rolled steel, steel coated with zinc metal, zinc compounds, or zinc alloys, such as electrogalvanized steel, hot-dipped galvanized steel, galvanealed steel, and steel plated with zinc alloy. 
     In certain embodiments, the multi-metal assembly is first cleaned to remove grease, dirt, oil and any other undesirable compounds that may interfere with coating formation. In certain of these embodiments, the cleaner used is a two part cleaner (alkaline cleaner and surfactant package), such as CK2010LP/CK181ALP, commercially available from PPG Industries, Inc., used at a concentration ratio of 1:0.1 alkaline cleaner:surfactant package and a temperature of 125° F. (52° C.). The metal substrate may first be spray cleaned for one minute and immersion cleaned for two minutes, followed by a one minute rinse water spray to remove the cleaner from the surface. 
     In certain embodiments, the multi-metal assembly is next treated with an activating rinse, or rinse conditioner (RC), that activates the surface of the substrate with colloidal Ti particles so that the phosphate crystals grow uniformly and helps to achieve the correct crystal morphology. In certain of these embodiments, a powder rinse conditioner is utilized at a concentration of lg/L (Ti between 1.0 and 3.5ppm), and the pH is adjusted to between 8.00 and 9.50. In certain embodiments, the multi-metal assembly is immersed in this stage, at ambient temperature, for one minute before entering the zinc phosphate bath. 
     In the methods of the present invention the multi-metal assembly is treated by contacting the substrate with a zinc-phosphate composition that includes a group IIIB and/or group IVB metal, such as zirconium, titanium, hafnium, yttrium, cerium, or a mixture thereof. More particularly, in certain embodiments, the zinc phosphate composition comprises: (1) phosphate ions; (2) zinc ions; (3) free fluoride; and (4) a Group IIIB and/or IVB metal, such as zirconium. 
     As previously indicated, the zinc-phosphate compositions used in the methods of the present invention comprise phosphate, PO 4   3− , ions. In certain embodiments, the zinc-phosphate composition comprises at least 5,000 ppm, such as 5,000-20,000 ppm phosphate ions, such as 10,000-20,000 ppm phosphate ions. The source of phosphate ions may be any material or compound known to those skilled in the art to ionize in aqueous acidic solutions to form anions such as (PO 4 ) −3  from simple compounds as well as condensed phosphoric acids, including salts thereof. Nonexclusive examples of such sources include: phosphoric acid, alkali metal phosphates such as monosodium phosphate, monopotassium phosphate, disodium phosphate, divalent metal phosphates and the like, as well as mixtures thereof. 
     The zinc-phosphate compositions used in the methods of the present invention also comprise zinc ions. In certain embodiments, the zinc-phosphate composition comprises at least 700 ppm, such as 700 to 2000 ppm, such as 700 to 1300 ppm Zn ions. The source of the zinc ion may be one or more conventional zinc ion sources known in the art, such as zinc, zinc nitrate, zinc oxide, zinc carbonate, and even zinc phosphate, to the extent of solubility, and the like. With the use of the zinc phosphate, the quantitative range of the total acid is maintained by a reduced amount of phosphate ion from the other phosphate sources. 
     The zinc-phosphate compositions used in the methods of the present invention also comprise free fluoride (F), such as 100 to 300 ppm free fluoride, 100 to 200 ppm free fluoride, 110 to 200 ppm free fluoride, 120 to 180 ppm free fluoride, or, in some cases, 140 to 180 ppm free fluoride. The source of fluoride ion may be any fluoride-containing compound including monofluorides, bifluorides, fluoride complexes, and mixtures thereof known to generate fluoride ions. Examples include ammonium and alkali metal fluorides, acid fluorides, fluoroboric, fluorosilicic, fluorotitanic, and fluorozirconic acids and their ammonium and alkali metal salts, and other inorganic fluorides, nonexclusive examples of which are: zinc fluoride, zinc aluminum fluoride, titanium fluoride, zirconium fluoride, nickel fluoride, ammonium fluoride, sodium fluoride, potassium fluoride, and hydrofluoric acid, as well as other similar materials known to those skilled in the art. 
     The zinc-phosphate compositions used in the methods of the present invention also comprise a group IIIB and/or group IVB metal, such as zirconium, titanium, hafnium, yttrium, cerium or a mixture thereof. In certain embodiments, the zinc-phosphate composition comprises a compound of zirconium that is present in the zinc-phosphate composition in an amount such that a ratio of the concentration of free fluoride in the composition, in ppm, to the concentration of zirconium in the composition, in ppm, is at least 2.5 to 1, such as at least 3:1, at least 4:1, at least 5:1, or, in some cases, at least 10:1. 
     In certain embodiments, the amount of group IIIB and/or IVB metal, such as zirconium, in the zinc-phosphate composition is no more than 100 ppm, such as no more than 80 ppm, no more than 60 ppm, no more than 55 ppm, or, in some cases, no more than 10 ppm. In certain of these embodiments, the amount of group IIIB and/or IVB metal, such as zirconium, in the zinc-phosphate composition is at least 1 ppm, at least 8 ppm, or, in some cases, at least 40 ppm, or at least 45 ppm. 
     In certain embodiments of the zinc-phosphate compositions used in the methods of the present invention, the ratio of the moles per liter of free fluoride in the composition to the square root of the moles per liter of zirconium in the composition is greater than 10, such as at least 11, at least 12, or, in some cases, at least 15. In certain of these embodiments, the zinc-phosphate composition does not include titanium or, if titanium is included, the ratio of the moles per liter of free fluoride in the composition to the square root of the moles per liter of titanium is greater than 14, such as at least 15, at least 16, or, in some cases, at least 18. 
     The source of zirconium may be zirconium itself or a compound of zirconium such as, for example, hexafluorozirconic acid, alkali metal and ammonium salts thereof, ammonium zirconium carbonate, zirconyl nitrate, zirconium carboxylates and zirconium hydroxy carboxylates, such as hydrofluorozirconic acid, zirconium acetate, zirconium oxalate, ammonium zirconium glycolate, ammonium zirconium lactate, ammonium zirconium citrate, and mixtures thereof. Suitable compounds of titanium include, but are not limited to, fluorotitanic acid and its salts. A suitable compound of hafnium includes, but is not limited to, hafnium nitrate. A suitable compound of yttrium includes, but is not limited to, yttrium nitrate. A suitable compound of cerium includes, but is not limited to, cerous nitrate. 
     The pH of the zinc-phosphate composition often ranges from 2.0 to 7.0, such as 3.0 to 5.0. 
     In certain embodiments, the zinc-phosphate compositions used in the methods of the present invention may comprise nitrate ion and one or more of various metal ions, such as ferrous ion, nickel ion, cobalt ion, manganese ion, tungsten ion, and the like. For example, in certain embodiments, the zinc-phosphate composition comprises 300-900 ppm (such as 700-900 ppm) Mn, 250-1100 ppm (such as 250 to 750 ppm, such as 250-500 ppm) Ni, 200-600 ppm total fluorine, and up to 15 ppm Fe. With the zinc phosphate composition bath operating within these parameters, it is possible to achieve coating weights on non-aluminum substrates that are within the specifications of the automotive industry, while preventing any significant coating from forming on the aluminum substrate during this treatment step. Thus, in certain embodiments of the methods of the present invention, the multi-metal assembly, after treatment with the zinc-phosphate composition, has a coating, such as a crystalline zinc-phosphate coating, on the portion comprising the non-aluminum metal substrate that has a coating weight of at least 0.5 g/m 2 , such as 0.5 g/m 2  to 10 g/m 2 , or, in some cases, 1 g/m 2  to 5 g/m 2 , but a coating, such as a continuous amorphous layer, on the portion comprising an aluminum substrate that has a coating weight no more than 0.5 g/m 2 , such as less than 0.5 g/m 2 , no more than 0.25 g/m 2 , such as no more than 0.1 g/m 2 , such as 0.05 g/m 2  or less. 
     In certain embodiments, the zinc-phosphate composition is immersion applied, at, for example, 120-125° F. (49-52° C.), for two minutes, and, in some embodiments, is followed by a 30 second rinse before the aluminum coating phase described below. In certain embodiments, the amount of free fluoride, in ppm, in the zinc-phosphate composition is greater than 8000/T, such as at least 8010/T, at least 8020/T, or at least 8030/T, wherein T is the temperature of the zinc-phosphate composition in ° C. 
     In accordance with embodiments of the present invention, as noted above, the treated multi-metal assembly is contacted with a composition comprising: (i) a Group IIIB and/or IVB metal; and (ii) free fluoride. In certain embodiments, such a composition comprises: (i) fluorozirconic acid; (ii) a second source of fluoride ions. In certain embodiments, this composition is contains 1-3% by weight solids, based on total composition weight and has a pH of 4.60-5.40. 
     The source of Group IIIB and/or IVB metal in this composition can, for example, be any of the sources described above with respect to the zinc-phosphate composition. In certain embodiments, this source is fluorozirconic acid. In certain embodiments, this composition comprises at least 10 ppm metal, such as zirconium, at least 100 ppm metal, such as zirconium, or, in some cases, at least 150 ppm metal, such as zirconium (measured as elemental metal). In certain embodiments, this composition comprises no more than 5000 ppm metal, such as zirconium, no more than 300 ppm metal, such as zirconium, or, in some cases, no more than 250 ppm metal or no more than 200 ppm metal, such as zirconium (measured as elemental metal). 
     In certain embodiments, the composition further includes an electropositive metal. As used herein, the term “electropositive metal” refers to metals that are more electropositive than the metal substrate. This means that, for purposes of the present invention, the term “electropositive metal” encompasses metals that are less easily oxidized than the metal of the metal substrate that is being treated. As will be appreciated by those skilled in the art, the tendency of a metal to be oxidized is called the oxidation potential, is expressed in volts, and is measured relative to a standard hydrogen electrode, which is arbitrarily assigned an oxidation potential of zero. The oxidation potential for several elements is set forth in the table below. An element is less easily oxidized than another element if it has a voltage value, E*, in the following table, that is greater than the element to which it is being compared. 
     
       
         
           
               
               
               
             
               
                   
               
               
                 Element 
                 Half-cell reaction 
                 Voltage, E* 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 Potassium 
                 K +  + e → K 
                 −2.93 
               
               
                 Calcium 
                 Ca 2+  + 2e → Ca 
                 −2.87 
               
               
                 Sodium 
                 Na +  + e → Na 
                 −2.71 
               
               
                 Magnesium 
                 Mg 2+  + 2e → Mg 
                 −2.37 
               
               
                 Aluminum 
                 Al 3+  + 3e → Al 
                 −1.66 
               
               
                 Zinc 
                 Zn 2+  + 2e → Zn 
                 −0.76 
               
               
                 Iron 
                 Fe 2+  + 2e → Fe 
                 −0.44 
               
               
                 Nickel 
                 Ni 2+  + 2e → Ni 
                 −0.25 
               
               
                 Tin 
                 Sn 2+  + 2e → Sn 
                 −0.14 
               
               
                 Lead 
                 Pb 2+  + 2e → Pb 
                 −0.13 
               
               
                 Hydrogen 
                 2H +  + 2e → H 2   
                 −0.00 
               
               
                 Copper 
                 Cu 2+  + 2e → Cu 
                 0.34 
               
               
                 Mercury 
                 Hg 2   2+  + 2e → 2Hg 
                 0.79 
               
               
                 Silver 
                 Ag +  + e → Ag 
                 0.80 
               
               
                 Gold 
                 Au 3+  + 3e → Au 
                 1.50 
               
               
                   
               
            
           
         
       
     
     Thus, as will be apparent, suitable electropositive metals for inclusion in the composition include, for example, nickel, copper, silver, and gold, as well mixtures thereof. 
     In certain embodiments, the source of electropositive metal in the pretreatment composition is a water soluble metal salt, such as any of the water soluble copper compounds mentioned in U.S. Patent Application Publication No 2009/0032144 A1at [0022]-[0025], the cited portion of which being incorporated herein by reference. 
     In certain embodiments, the electropositive metal, such as copper, is included in the composition in an amount of at least 1 ppm, such as at least 5 ppm, or in some cases, at least 10 ppm, at least 20 ppm, or at least 25 ppm of total metal (measured as elemental metal). In certain embodiments, the electropositive metal is included in the composition in an amount of no more than 500 ppm, such as no more than 100 ppm, or in some cases, no more than 50 ppm or no more than 35 ppm of total metal (measured as elemental metal). 
     The composition also comprises free fluoride. As will be appreciated, the source of free fluoride in the composition can vary. For example, in some cases, the free fluoride may derive from the group IIIB and/or IVB metal compound used in the composition, such as is the case, for example, with hexafluorozirconic acid. As the group IIIB and/or IVB metal is deposited upon the metal substrate, fluorine in the hexafluorozirconic acid will become free fluoride and, as will be appreciated, the level of free fluoride in the pretreatment composition will, if left unchecked, increase with time as metal is treated with the composition. In the methods of the present invention, the level of free fluoride in the composition is maintained at a concentration of no less than 0.1 ppm, in some cases no less than 20 ppm, in some cases no less than 50 ppm or no less than 100 ppm. In certain of these embodiments, the level of free fluoride is maintained at a concentration of no more than 300 ppm, in some cases no more than 200 ppm or no more than 150 ppm. 
     In certain embodiments, such as where fluorozirconic acid is used as the source of zirconium and the composition has no more than 300 ppm, such as no more than 200 ppm, zirconium, but also has at least 50 ppm, such as at least 100 ppm, free fluoride, the composition must have a second source of fluoride ions. Non-limiting examples of suitable such second sources of fluoride ions include HF, NH 4 F, NH 4 HF 2 , NaF, and/or NaHF 2 . As a result, in certain embodiments of the present invention the composition comprises: (i) fluorozirconic acid, and (ii) a second source of fluoride ions. 
     In certain embodiments, the composition comprises a resinous binder. Suitable resins include reaction products of one or more alkanolamines and an epoxy-functional material containing at least two epoxy groups, such as those disclosed in U.S. Pat. No. 5,653,823. In some cases, such resins contain beta hydroxy ester, imide, or sulfide functionality, incorporated by using dimethylolpropionic acid, phthalimide, or mercaptoglycerine as an additional reactant in the preparation of the resin. Alternatively, the reaction product is that of the diglycidyl ether of Bisphenol A (commercially available from Shell Chemical Company as EPON 880), dimethylol propionic acid, and diethanolamine in a 0.6 to 5.0:0.05 to 5.5:1 mole ratio. Other suitable resinous binders include water soluble and water dispersible polyacrylic acids as disclosed in U.S. Pat. Nos. 3,912,548 and 5,328,525; phenol formaldehyde resins as described in U.S. Pat. No. 5,662,746; water soluble polyamides such as those disclosed in WO 95/33869; copolymers of maleic or acrylic acid with allyl ether as described in Canadian patent application 2,087,352; and water soluble and dispersible resins including epoxy resins, aminoplasts, phenol-formaldehyde resins, tannins, and polyvinyl phenols as discussed in U.S. Pat. No. 5,449,415. 
     In these embodiments of the present invention, the resinous binder is present in the composition in an amount of 0.005 percent to 30 percent by weight, such as 0.5 to 3 percent by weight, based on the total weight of the ingredients in the composition. 
     In other embodiments, however, the composition is substantially free or, in some cases, completely free of any resinous binder. As used herein, the term “substantially free”, when used with reference to the absence of resinous binder in the composition, means that any resinous binder is present in the composition in an amount of less than 0.005 percent by weight. As used herein, the term “completely free” means that there is no resinous binder in the composition at all. 
     The composition may optionally contain other materials, such as nonionic surfactants and auxiliaries conventionally used in the art of pretreatment. In an aqueous medium, water dispersible organic solvents, for example, alcohols with up to about 8 carbon atoms, such as methanol, isopropanol, and the like, may be present; or glycol ethers such as the monoalkyl ethers of ethylene glycol, diethylene glycol, or propylene glycol, and the like. When present, water dispersible organic solvents are typically used in amounts up to about ten percent by volume, based on the total volume of aqueous medium. 
     Other optional materials include surfactants that function as defoamers or substrate wetting agents. 
     In certain embodiments, the composition also comprises a reaction accelerator, such as nitrite ions, nitrate ions, nitro-group containing compounds, hydroxylamine sulfate, persulfate ions, sulfite ions, hyposulfite ions, peroxides, iron (III) ions, citric acid iron compounds, bromate ions, perchlorinate ions, chlorate ions, chlorite ions as well as ascorbic acid, citric acid, tartaric acid, malonic acid, succinic acid and salts thereof. 
     In certain embodiments, the composition also comprises a filler, such as a siliceous filler. Non-limiting examples of suitable fillers include silica, mica, montmorillonite, kaolinite, asbestos, talc, diatomaceous earth, vermiculite, natural and synthetic zeolites, cement, calcium silicate, aluminum silicate, sodium aluminum silicate, aluminum polysilicate, alumina silica gels, and glass particles. In addition to the siliceous fillers other finely divided particulate substantially water-insoluble fillers may also be employed. Examples of such optional fillers include carbon black, charcoal, graphite, titanium oxide, iron oxide, copper oxide, zinc oxide, antimony oxide, zirconia, magnesia, alumina, molybdenum disulfide, zinc sulfide, barium sulfate, strontium sulfate, calcium carbonate, and magnesium carbonate. 
     In certain embodiments, the composition comprises phosphate ions. In certain embodiments, phosphate ions are present in an amount of 10 to 500 ppm, such as 25 to 200 ppm phosphate ion. Exemplary sources of phosphate ion include those sources mentioned above with respect to the zinc-phosphate composition. In certain embodiments, however, the composition is substantially or, in some cases, completely free of phosphate ion. As used herein, the term “substantially free” when used in reference to the absence of phosphate ion in the composition, means that phosphate ion is present in the composition in an amount less than 10 ppm. As used herein, the term “completely free”, when used with reference to the absence of phosphate ions, means that there are no phosphate ions in the composition at all. 
     In certain embodiments, the composition is substantially or, in some cases, completely free of chromate and/or heavy metal phosphate, such as zinc phosphate. As used herein, the term “substantially free” when used in reference to the absence of chromate and/or heavy metal phosphate in the composition, means that these substances are not present in the composition to such an extent that they cause a burden on the environment. That is, they are not substantially used and the formation of sludge, such as zinc phosphate, formed in the case of use of a treating agent based on zinc phosphate, is eliminated. As used herein, the term “completely free”, when used with reference to the absence of a heavy metal phosphate and/or chromate, means that there is no heavy metal phosphate and/or chromate in the composition at all. 
     Moreover, in certain embodiments, the composition is substantially free, or, in some cases, completely free of any organic materials. As used herein, the term “substantially free”, when used with reference to the absence of organic materials in the composition, means that any organic materials are present in the composition, if at all, as an incidental impurity. In other words, the presence of any organic material does not affect the properties of the composition. As used herein, the term “completely free”, when used with reference to the absence of organic material, means that there is no organic material in the composition at all. 
     In certain embodiments, the film coverage of the residue of the composition generally ranges from 0.1 to 1000 milligrams per square meter (mg/m 2 ), such as 10 to 400 mg/m 2 . Following contact with the composition, the multi-metal assembly may be rinsed with water and dried. 
     In certain embodiments of the methods of the present invention, the multi-metal assembly can then be contacted with a coating composition comprising a film-forming resin. Any suitable technique may be used to contact the substrate with such a coating composition, including, for example, brushing, dipping, flow coating, spraying and the like. In certain embodiments, however, as described in more detail below, such contacting comprises an electrocoating step wherein an electrodepositable composition is deposited onto the metal substrate by electrodeposition. 
     As used herein, the term “film-forming resin” refers to resins that can form a self-supporting continuous film on at least a horizontal surface of a substrate upon removal of any diluents or carriers present in the composition or upon curing at ambient or elevated temperature. Conventional film-forming resins that may be used include, without limitation, those typically used in automotive OEM coating compositions, automotive refinish coating compositions, industrial coating compositions, architectural coating compositions, coil coating compositions, and aerospace coating compositions, among others. 
     In certain embodiments, the coating composition comprises a thermosetting film-forming resin. As used herein, the term “thermosetting” refers to resins that “set” irreversibly upon curing or crosslinking, wherein the polymer chains of the polymeric components are joined together by covalent bonds. This property is usually associated with a cross-linking reaction of the composition constituents often induced, for example, by heat or radiation. Curing or crosslinking reactions also may be carried out under ambient conditions. Once cured or crosslinked, a thermosetting resin will not melt upon the application of heat and is insoluble in solvents. In other embodiments, the coating composition comprises a thermoplastic film-forming resin. As used herein, the term “thermoplastic” refers to resins that comprise polymeric components that are not joined by covalent bonds and thereby can undergo liquid flow upon heating and are soluble in solvents. 
     As previously indicated, in certain embodiments, the substrate is contacted with a coating composition comprising a film-forming resin by an electrocoating step wherein an electrodepositable composition is deposited onto the metal substrate by electrodeposition. In the process of electrodeposition, the metal substrate being treated, serving as an electrode, and an electrically conductive co unter electrode are placed in contact with an ionic, electrodepositable composition. Upon passage of an electric current between the electrode and counter electrode while they are in contact with the electrodepositable composition, an adherent film of the electrodepositable composition will deposit in a substantially continuous manner on the metal substrate. 
     Electrodeposition is usually carried out at a constant voltage in the range of from 1 volt to several thousand volts, typically between 50 and 500 volts. Current density is usually between 1.0 ampere and 15 amperes per square foot (10.8 to 161.5 amperes per square meter) and tends to decrease quickly during the electrodeposition process, indicating formation of a continuous self-insulating film. 
     The electrodepositable composition used in certain embodiments of the present invention often comprises a resinous phase dispersed in an aqueous medium where the resinous phase comprises: (a) an active hydrogen group-containing ionic electrodepositable resin, and (b) a curing agent having functional groups reactive with the active hydrogen groups of (a). 
     In certain embodiments, the electrodepositable compositions utilized in certain embodiments of the present invention contain, as a main film-forming polymer, an active hydrogen-containing ionic, often cationic, electrodepositable resin. A wide variety of electrodepositable film-forming resins are known and can be used in the present invention so long as the polymers are “water dispersible,” i.e., adapted to be solubilized, dispersed or emulsified in water. The water dispersible polymer is ionic in nature, that is, the polymer will contain anionic functional groups to impart a negative charge or, as is often preferred, cationic functional groups to impart a positive charge. 
     Examples of film-forming resins suitable for use in anionic electrodepositable compositions are base-solubilized, carboxylic acid containing polymers, such as the reaction product or adduct of a drying oil or semi-drying fatty acid ester with a dicarboxylic acid or anhydride; and the reaction product of a fatty acid ester, unsaturated acid or anhydride and any additional unsaturated modifying materials which are further reacted with polyol. Also suitable are the at least partially neutralized interpolymers of hydroxy-alkyl esters of unsaturated carboxylic acids, unsaturated carboxylic acid and at least one other ethylenically unsaturated monomer. Still another suitable electrodepositable film-forming resin comprises an alkyd-aminoplast vehicle, i.e., a vehicle containing an alkyd resin and an amine-aldehyde resin. Yet another anionic electrodepositable resin composition comprises mixed esters of a resinous polyol, such as is described in U.S. Pat. No. 3,749,657 at col. 9, lines 1 to 75 and col. 10, lines 1 to 13, the cited portion of which being incorporated herein by reference. Other acid functional polymers can also be used, such as phosphatized polyepoxide or phosphatized acrylic polymers as are known to those skilled in the art. 
     As aforementioned, it is often desirable that the active hydrogen-containing ionic electrodepositable resin (a) is cationic and capable of deposition on a cathode. Examples of such cationic film-forming resins include amine salt group-containing resins, such as the acid-solubilized reaction products of polyepoxides and primary or secondary amines, such as those described in U.S. Pat. Nos. 3,663,389; 3,984,299; 3,947,338; and 3,947,339. Often, these amine salt group-containing resins are used in combination with a blocked isocyanate curing agent. The isocyanate can be fully blocked, as described in U.S. Pat. No. 3,984,299, or the isocyanate can be partially blocked and reacted with the resin backbone, such as is described in U.S. Pat. No. 3,947,338. Also, one-component compositions as described in U.S. Pat. No. 4,134,866 and DE-OS No. 2,707,405 can be used as the film-forming resin. Besides the epoxy-amine reaction products, film-forming resins can also be selected from cationic acrylic resins, such as those described in U.S. Pat. Nos. 3,455,806 and 3,928,157. 
     Besides amine salt group-containing resins, quaternary ammonium salt group-containing resins can also be employed, such as those formed from reacting an organic polyepoxide with a tertiary amine salt as described in U.S. Pat. Nos. 3,962,165; 3,975,346; and 4,001,101. Examples of other cationic resins are ternary sulfonium salt group-containing resins and quaternary phosphonium salt-group containing resins, such as those described in U.S. Pat. Nos. 3,793,278 and 3,984,922, respectively. Also, film-forming resins which cure via transesterification, such as described in European Application No. 12463 can be used. Further, cationic compositions prepared from Mannich bases, such as described in U.S. Pat. No. 4,134,932, can be used. 
     In certain embodiments, the resins present in the electrodepositable composition are positively charged resins which contain primary and/or secondary amine groups, such as described in U.S. Pat. Nos. 3,663,389; 3,947,339; and 4,116,900. In U.S. Pat. No. 3,947,339, a polyketimine derivative of a polyamine, such as diethylenetriamine or triethylenetetraamine, is reacted with a polyepoxide. When the reaction product is neutralized with acid and dispersed in water, free primary amine groups are generated. Also, equivalent products are formed when polyepoxide is reacted with excess polyamines, such as diethylenetriamine and triethylenetetraamine, and the excess polyamine vacuum stripped from the reaction mixture, as described in U.S. Pat. Nos. 3,663,389 and 4,116,900. 
     In certain embodiments, the active hydrogen-containing ionic electrodepositable resin is present in the electrodepositable composition in an amount of 1 to 60 percent by weight, such as 5 to 25 percent by weight, based on total weight of the electrodeposition bath. 
     As indicated, the resinous phase of the electrodepositable composition often further comprises a curing agent adapted to react with the active hydrogen groups of the ionic electrodepositable resin. For example, both blocked organic polyisocyanate and aminoplast curing agents are suitable for use in the present invention, although blocked isocyanates are often preferred for cathodic electrodeposition. 
     Aminoplast resins, which are often the preferred curing agent for anionic electrodeposition, are the condensation products of amines or amides with aldehydes. Examples of suitable amine or amides are melamine, benzoguanamine, urea and similar compounds. Generally, the aldehyde employed is formaldehyde, although products can be made from other aldehydes, such as acetaldehyde and furfural. The condensation products contain methylol groups or similar alkylol groups depending on the particular aldehyde employed. Often, these methylol groups are etherified by reaction with an alcohol, such as a monohydric alcohol containing from 1 to 4 carbon atoms, such as methanol, ethanol, isopropanol, and n-butanol. Aminoplast resins are commercially available from American Cyanamid Co. under the trademark CYMEL and from Monsanto Chemical Co. under the trademark RESIMENE. 
     The aminoplast curing agents are often utilized in conjunction with the active hydrogen containing anionic electrodepositable resin in amounts ranging from 5 percent to 60 percent by weight, such as from 20 percent to 40 percent by weight, the percentages based on the total weight of the resin solids in the electrodepositable composition. 
     As indicated, blocked organic polyisocyanates are often used as the curing agent in cathodic electrodeposition compositions. The polyisocyanates can be fully blocked as described in U.S. Pat. No. 3,984,299 at col. 1, lines 1 to 68, col. 2, and col. 3, lines 1 to 15, or partially blocked and reacted with the polymer backbone as described in U.S. Pat. No. 3,947,338 at col. 2, lines 65 to 68, col. 3, and col. 4 lines 1 to 30, the cited portions of which being incorporated herein by reference. By “blocked” is meant that the isocyanate groups have been reacted with a compound so that the resultant blocked isocyanate group is stable to active hydrogens at ambient temperature but reactive with active hydrogens in the film forming polymer at elevated temperatures usually between 90° C. and 200° C. 
     Suitable polyisocyanates include aromatic and aliphatic polyisocyanates, including cycloaliphatic polyisocyanates and representative examples include diphenylmethane-4,4′-diisocyanate (MDI), 2,4- or 2,6-toluene diisocyanate (TDI), including mixtures thereof, p-phenylene diisocyanate, tetramethylene and hexamethylene diisocyanates, dicyclohexylmethane-4,4′-diisocyanate, isophorone diisocyanate, mixtures of phenylmethane-4,4′-diisocyanate and polymethylene polyphenylisocyanate. Higher polyisocyanates, such as triisocyanates can be used. An example would include triphenylmethane-4,4′,4″-triisocyanate. Isocyanate ( )-prepolymers with polyols such as neopentyl glycol and trimethylolpropane and with polymeric polyols such as polycaprolactone diols and triols (NCO/OH equivalent ratio greater than 1) can also be used. 
     The polyisocyanate curing agents are typically utilized in conjunction with the active hydrogen containing cationic electrodepositable resin in amounts ranging from 5 percent to 60 percent by weight, such as from 20 percent to 50 percent by weight, the percentages based on the total weight of the resin solids of the electrodepositable composition. 
     In certain embodiments, the coating composition comprising a film-forming resin also comprises yttrium. In certain embodiments, yttrium is present in such compositions in an amount from 10 to 10,000 ppm, such as not more than 5,000 ppm, and, in some cases, not more than 1,000 ppm, of total yttrium (measured as elemental yttrium). 
     Both soluble and insoluble yttrium compounds may serve as the source of yttrium. Examples of yttrium sources suitable for use in lead-free electrodepositable coating compositions are soluble organic and inorganic yttrium salts such as yttrium acetate, yttrium chloride, yttrium formate, yttrium carbonate, yttrium sulfamate, yttrium lactate and yttrium nitrate. When the yttrium is to be added to an electrocoat bath as an aqueous solution, yttrium nitrate, a readily available yttrium compound, is a preferred yttrium source. Other yttrium compounds suitable for use in electrodepositable compositions are organic and inorganic yttrium compounds such as yttrium oxide, yttrium bromide, yttrium hydroxide, yttrium molybdate, yttrium sulfate, yttrium silicate, and yttrium oxalate. Organoyttrium complexes and yttrium metal can also be used. When the yttrium is to be incorporated into an electrocoat bath as a component in the pigment paste, yttrium oxide is often the preferred source of yttrium. 
     The electrodepositable compositions described herein are in the form of an aqueous dispersion. The term “dispersion” is believed to be a two-phase transparent, translucent or opaque resinous system in which the resin is in the dispersed phase and the water is in the continuous phase. The average particle size of the resinous phase is generally less than 1.0 and usually less than 0.5 microns, often less than 0.15 micron. 
     The concentration of the resinous phase in the aqueous medium is often at least 1 percent by weight, such as from 2 to 60 percent by weight, based on total weight of the aqueous dispersion. When such compositions are in the form of resin concentrates, they generally have a resin solids content of 20 to 60 percent by weight based on weight of the aqueous dispersion. 
     The electrodepositable compositions described herein are often supplied as two components: (1) a clear resin feed, which includes generally the active hydrogen-containing ionic electrodepositable resin, i.e., the main film-forming polymer, the curing agent, and any additional water-dispersible, non-pigmented components; and (2) a pigment paste, which generally includes one or more colorants (described below), a water-dispersible grind resin which can be the same or different from the main-film forming polymer, and, optionally, additives such as wetting or dispersing aids. Electrodeposition bath components (1) and (2) are dispersed in an aqueous medium which comprises water and, usually, coalescing solvents. 
     As aforementioned, besides water, the aqueous medium may contain a coalescing solvent. Useful coalescing solvents are often hydrocarbons, alcohols, esters, ethers and ketones. The preferred coalescing solvents are often alcohols, polyols and ketones. Specific coalescing solvents include isopropanol, butanol, 2-ethylhexanol, isophorone, 2-methoxypentanone, ethylene and propylene glycol and the monoethyl monobutyl and monohexyl ethers of ethylene glycol. The amount of coalescing solvent is generally between 0.01 and 25 percent, such as from 0.05 to 5 percent by weight based on total weight of the aqueous medium. 
     In addition, a colorant and, if desired, various additives such as surfactants, wetting agents or catalyst can be included in the coating composition comprising a film-forming resin. As used herein, the term “colorant” means any substance that imparts color and/or other opacity and/or other visual effect to the composition. The colorant can be added to the composition in any suitable form, such as discrete particles, dispersions, solutions and/or flakes. A single colorant or a mixture of two or more colorants can be used. 
     Example colorants include pigments, dyes and tints, such as those used in the paint industry and/or listed in the Dry Color Manufacturers Association (DCMA), as well as special effect compositions. A colorant may include, for example, a finely divided solid powder that is insoluble but wettable under the conditions of use. A colorant can be organic or inorganic and can be agglomerated or non-agglomerated. Colorants can be incorporated by use of a grind vehicle, such as an acrylic resin, the use of which will be familiar to one skilled in the art. 
     Example pigments and/or pigment compositions include, but are not limited to, carbazole dioxazine crude pigment, azo, monoazo, disazo, naphthol AS, salt type (lakes), benzimidazolone, condensation, metal complex, isoindolinone, isoindoline and polycyclic phthalocyanine, quinacridone, perylene, perinone, diketopyrrolo pyrrole, thioindigo, anthraquinone, indanthrone, anthrapyrimidine, flavanthrone, pyranthrone, anthanthrone, dioxazine, triarylcarbonium, quinophthalone pigments, diketo pyrrolo pyrrole red (“DPPBO red”), titanium dioxide, carbon black and mixtures thereof. The terms “pigment” and “colored filler” can be used interchangeably. 
     Example dyes include, but are not limited to, those that are solvent and/or aqueous based such as phthalo green or blue, iron oxide, bismuth vanadate, anthraquinone, perylene, aluminum and quinacridone. 
     Example tints include, but are not limited to, pigments dispersed in water-based or water miscible carriers such as AQUA-CHEM 896 commercially available from Degussa, Inc., CHARISMA COLORANTS and MAXITONER INDUSTRIAL COLORANTS commercially available from Accurate Dispersions division of Eastman Chemical, Inc. 
     As noted above, the colorant can be in the form of a dispersion including, but not limited to, a nanoparticle dispersion. Nanoparticle dispersions can include one or more highly dispersed nanoparticle colorants and/or colorant particles that produce a desired visible color and/or opacity and/or visual effect. Nanoparticle dispersions can include colorants such as pigments or dyes having a particle size of less than 150 nm, such as less than 70 nm, or less than 30 nm. Nanoparticles can be produced by milling stock organic or inorganic pigments with grinding media having a particle size of less than 0.5 mm. Example nanoparticle dispersions and methods for making them are identified in U.S. Pat. No. 6,875,800 B2, which is incorporated herein by reference. Nanoparticle dispersions can also be produced by crystallization, precipitation, gas phase condensation, and chemical attrition (i.e., partial dissolution). In order to minimize re-agglomeration of nanoparticles within the coating, a dispersion of resin-coated nanoparticles can be used. As used herein, a “dispersion of resin-coated nanoparticles” refers to a continuous phase in which is dispersed discreet “composite microparticles” that comprise a nanoparticle and a resin coating on the nanoparticle. Example dispersions of resin-coated nanoparticles and methods for making them are identified in United States Patent Application Publication 2005-0287348 A1, filed Jun. 24, 2004, U.S. Provisional Application No. 60/482,167 filed Jun. 24, 2003, and U.S. patent application Ser. No. 11/337,062, filed Jan. 20, 2006, which is also incorporated herein by reference. 
     Example special effect compositions that may be used include pigments and/or compositions that produce one or more appearance effects such as reflectance, pearlescence, metallic sheen, phosphorescence, fluorescence, photochromism, photosensitivity, thermochromism, goniochromism and/or color-change. Additional special effect compositions can provide other perceptible properties, such as opacity or texture. In certain embodiments, special effect compositions can produce a color shift, such that the color of the coating changes when the coating is viewed at different angles. Example color effect compositions are identified in U.S. Pat. No. 6,894,086, incorporated herein by reference. Additional color effect compositions can include transparent coated mica and/or synthetic mica, coated silica, coated alumina, a transparent liquid crystal pigment, a liquid crystal coating, and/or any composition wherein interference results from a refractive index differential within the material and not because of the refractive index differential between the surface of the material and the air. 
     In certain embodiments, a photosensitive composition and/or photochromic composition, which reversibly alters its color when exposed to one or more light sources, can be used. Photochromic and/or photosensitive compositions can be activated by exposure to radiation of a specified wavelength. When the composition becomes excited, the molecular structure is changed and the altered structure exhibits a new color that is different from the original color of the composition. When the exposure to radiation is removed, the photochromic and/or photosensitive composition can return to a state of rest, in which the original color of the composition returns. In certain embodiments, the photochromic and/or photosensitive composition is colorless in a non-excited state and exhibits a color in an excited state. Full color-change can appear within milliseconds to several minutes, such as from 20 to 60 seconds. Example photochromic and/or photosensitive compositions include photochromic dyes. 
     In certain embodiments, the photosensitive composition and/or photochromic composition can be associated with and/or at least partially bound to, such as by covalent bonding, a polymer and/or polymeric materials of a polymerizable component. In contrast to some coatings in which the photosensitive composition may migrate out of the coating and crystallize into the substrate, the photosensitive composition and/or photochromic composition associated with and/or at least partially bound to a polymer and/or polymerizable component in accordance with certain embodiments of the present invention, have minimal migration out of the coating. Example photosensitive compositions and/or photochromic compositions and methods for making them are identified in U.S. application Ser. No. 10/892,919 filed Jul. 16, 2004, incorporated herein by reference. 
     In general, the colorant can be present in the coating composition in any amount sufficient to impart the desired visual and/or color effect. The colorant may comprise from 1 to 65 weight percent, such as from 3 to 40 weight percent or 5 to 35 weight percent, with weight percent based on the total weight of the composition. 
     After deposition, the coating is often heated to cure the deposited composition. The heating or curing operation is often carried out at a temperature in the range of from 120 to 250° C., such as from 120 to 190° C., for a period of time ranging from 10 to 60 minutes. In certain embodiments, the thickness of the resultant film is from 10 to 50 microns. 
     EXAMPLES 
     The following examples illustrate exemplary embodiments of the invention. However, the examples are provided for illustrative purposes only, and do not limit the scope of the invention. Unless otherwise indicated, all parts and percentages in the following examples, as well as throughout the specification, are by weight. 
     Examples 1-6: Corrosion/Chip Resistance 
     Example 1 
     The following solutions were used in Example 1. 
     Solution A: A spray cleaner bath was prepared by adding water to a spray tank with V-jet nozzles that spray at a pressure of 15 psi located 8″ from the panel surface. 1.325 liter of Chemkleen 2010LP base cleaner (available from PPG Industries, Inc.) was placed into a 35 gallon reservoir of tap water and 132.5 milliliter of Chemkleen CK181ALP (available from PPG Industries, Inc.) was also placed into the cleaning tank. The solution was circulated and heated to the reported temperature in the table below. 
     Solution B: An immersion cleaner bath was made by adding water to a 20 gallon immersion tank with a circulating heater (Julaba brand). The heater/stirrer was the only form of recirculation in the bath. 757 ml of Chemkleen 2010LP base cleaner (available from PPG Industries, Inc.) was placed into a 20 gallon reservoir of tap water and 75 ml of Chemkleen CK181ALP (available from PPG Industries, Inc.) was also placed into the cleaning tank. The solution was circulated and heated to the reported temperature in the table below 
     Solution C: Tap Water was filled into a 35 gallon reservoir spray stage with vee jets spraying at 15 psi 8″ from the metal surface. 
     Solution D: An activating rinse was prepared by adding 75 gallons of water to 100 gallon immersion recirculating system. The circulation pump was started and a rinse conditioner slurry (1 lb Rinse Conditioner available from PPG Industries, Inc. thoroughly mixed with 1 gallon of water) was added. The final volume of the solution was adjusted to 100 gallon with water, the pH was measured and adjusted to 9.0-9.5 using Chemfil Buffer available from PPG Industries, Inc. 
     Solution E: zinc-phosphate composition was made using the ingredients and calculated amounts listed in Table 1 in a 100 gallon tank with circulating eductors. 
     
       
         
           
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Charge 
                 Description 
                 Calculated Amount 
               
               
                   
               
             
            
               
                 1 
                 CHEMFOS ® 700A 1   
                 3.7 gallon (37.0 lb)/100 gallon 
               
               
                   
                   
                 tank volume 
               
               
                 2 
                 CHEMFOS ®-FE 2   
                 0.068-1.36 fl. oz. (0.06-0.12 lb)/ 
               
               
                   
                   
                 100 gallon tank volume 
               
               
                 3 
                 CHEMFOS ® AZN 3   
                 0.13 gallon (1.625 lb)/100 gallon 
               
               
                   
                   
                 tank volume 
               
               
                 4 
                 CHEMFOS ® MAKE UP B 4   
                 1.6 gallon (17.3 lb)/100 gallon 
               
               
                   
                   
                 tank volume 
               
               
                 5 
                 CHEMFOS ® AFL 5   
                 0.27 gallon (2.46 lb)/100 gallon 
               
               
                   
                   
                 tank volume 
               
               
                   
               
               
                   1 Zinc phosphate solution available from PPG Industries Inc. 
               
               
                   2 A diiron tris(sulphate)-containing solution available from PPG Industries, Inc. 
               
               
                   3 Zinc nitrate-containing solution available from PPG Industries, Inc. 
               
               
                   4 A sodium dihydrogen orthophosphate, potassium dihydrogen orthophosphate and sodium nitrate-containing solution commercially available from PPG Industries, Inc. 
               
               
                   5 Ammonium bifluoride-containing solution available from PPG Industries, Inc. 
               
            
           
         
       
     
     First, water was added in an amount needed for bath makeup (100 gallons less the calculated volumes of other ingredients listed in Table 1). The circulation pump was started and charge 1 was added. Charge 2 was then added and the bath recirculated for 30 minutes. The solution was titrated for the initial free and total acid. If the free acid was less than 2.4 points, additional Charge 1 was added (0.25 gallons (2.5 lb.) per 100 gallons) until the free acid was greater than 2.4 points. Charge 3 was then added and excess free acid was neutralized by first adding one-half of the calculated amount of Charge 4 slowly with agitation. The solution was titrated for the free and total acid. If the free acid was greater than 0.9±0.1, then the remaining Charge 4 was added in small increments (10% of calculated charge amount) until the total acid was no greater than 17 or the final free acid range of 0.9±0.1 was reached. The solution was titrated for the free acid after each addition to be sure over neutralization did not occur. A 5% by weight solution of NaOH was added until a free acid point until the operating range of 0.6-1.0 was achieved. The final volume of the bath was adjusted to operating level and brought to a temperature of 50-54° C. to produce a bath having a free acid (FA) of 0.9±0.1 and Total Acid of 15-22 points. Additional charge 1 was added if necessary to increase the FA within the Free Acid and additional charge 4 was added to reduce the FA and increase the Total Acid. If the Total Acid &gt;17.0, then a 5% by weight solution of NaOH was added to reduce the Free Acid. At this point, the free fluoride concentration of the bath was measured. If the free fluoride concentration was &lt;200ppm then charge 5 was added until the free fluoride concentration was 200-300 ppm. Then, 0.72 lbs (315 milliliters) of Chemseal® 19 (a dihydrogen hexafluorozirconate-containing solution available from PPG Industries, Inc.) was added. Then, Chemfos® Liquid Additive 4.0 fl. oz. (0.4 lbs.) was added. The zinc-phosphate composition was measured to contain 1016 ppm Zn, 16 ppm Zr, 935 ppm Mn, 0.7 ml free acid, 18.6 ml total acid, 241 ppm free fluoride, 476 ppm total fluoride, and 420 ppm nickel. 
     Solution F: Tap Water was filled into a 35 gallon reservoir spray stage with vee jets spraying at 15 psi 8″ from the metal surface. 
     Solution G: A post rinse solution was prepared from a concentrate made of hexafluorozirconic acid, copper nitrate and ammonium bi-fluoride. The concentrate was added to a solution of deionized water to target 150-175 ppm Zr, 25-35 ppm Cu and 50-150 ppm Free Fluoride. The pH was adjusted with Chemfil Buffer a range between 4.6-5.4. This solution has a pH of 5.23, 104 ppm free fluoride, 170 ppm Zr, and 29.3 ppm Cu. It was made in a five gallon pail and circulated with an electric mixer. 
     Solution H: A deionized water rinse sprayed via whirljet nozzles 8″ from the panel surface via a solenoid valve. 
     A set of Aluminum alloy 6111, electro-galvanized steel, hot-dipped galvanized steel and cold-rolled steel panels was processed using the sequence set forth in Table 2. In the testing, the coating on Al 6111 was reduced to below 0.5 g/m 2  and the remaining metals remained at a level between 2.0 and 3.0 g/m 2  for the cold-rolled steel, electro galvanized and hot-dipped galvanized metal. 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                   
                   
                   
                   
                 Time in stage/ 
               
               
                 Stage 
                 Solution 
                 Temperature 
                 Application 
                 before next 
               
               
                   
               
             
            
               
                 1 
                 A 
                  52° C.  
                 Spray 
                 1:00 
               
               
                 2 
                 B 
                  50° C.  
                 immersion 
                 2:00 
               
               
                 3 
                 C 
                 ambient 
                 Spray 
                 1:00 
               
               
                 4 
                 D 
                 ambient 
                 immersion 
                 1:00 
               
               
                 5 
                 E 
                  52° C.  
                 immersion 
                 2:00 
               
               
                 6 
                 F 
                 ambient 
                 Spray 
                 0:30 
               
               
                 7 
                 G 
                 ambient 
                 immersion 
                 1:00 
               
               
                 Rinse 
                 H 
                 ambient 
                 Spray 
                 0:30 
               
               
                 Dry 
                   
                 150° C.  
                 Oven 
                 2:00 
               
               
                   
               
            
           
         
       
     
     Example 2 
     A set of Aluminum alloy 6111, electro-galvanized steel, hot-dipped galvanized steel and cold-rolled steel panels was processed using the sequence set forth in Table 2, except that Solution G was omitted. 
     Example 3 
     A set of Aluminum alloy 6111, electro-galvanized steel, hot-dipped galvanized steel and cold-rolled steel panels was processed using the sequence set forth in Table 2, with the following differences: (a) Solution E was prepared as described above with respect to Example 1, except that Charge 5 was omitted and the amount of Chemseal 19 used was 0.42 lbs (185 mis), thus resulting zinc-phosphate composition (for Solution E in this Example) was measured to contain 787 ppm Zn, 7 ppm Zr, 935 ppm Mn, 0.6 ml free acid, 14.7 ml total acid, 110 ppm free fluoride, 266 ppm total fluoride, and 421 ppm nickel; and Solution G was measured to have a pH of 5.10, 102 ppm free fluoride, 181 ppm Zr, and 28 ppm Cu. 
     Example 4 
     A set of Aluminum alloy 6111, electro-galvanized steel, hot-dipped galvanized steel and cold-rolled steel panels was processed using the sequence set forth in Table 2, with differences of Example 3 and with the further difference that Solution G was omitted. 
     Example 5 
     A set of Aluminum alloy 6111, electro-galvanized steel, hot-dipped galvanized steel and cold-rolled steel panels was processed using the sequence described in Table 2, with the following differences: (a) Solution E was prepared as described above with respect to Example 1 except that no Chemseal 19 was added; and (b) Solution G was replaced with Chemseal 59, a chrome-free rinse commercially available from PPG Industries, Inc. In this Example, Solution E had 1124 ppm Zn, 520 ppm Ni, 850 ppm Mn, 0.7 ml free acid, 15.0 ml total acid, 256 ppm free fluoride, 564 ppm total fluoride, and no Zr. Solution G had a pH of 4.90, 169 ppm total fluoride, 76 ppm Zr, and 0 ppm Cu. 
     Example 6 
     A set of Aluminum alloy 6111, electro-galvanized steel, hot-dipped galvanized steel and cold-rolled steel panels was processed as described in Example 5, except that the Chemseal 59 post rinse was omitted. 
     Examples 1-6 Testing 
     Panels processed according to Examples 1-6 were electro-coated with ED6280Z and topcoated using FCP6534 primer, UDCT 6466 basecoat, and TMAC8000 clearcoat (all available from PPG Industries, Inc.) according to the manufacturer&#39;s instructions. The panels were tested for corrosion resistance against Ford Motor Co. corrosion protocols of their cyclic corrosion test CETP L-467 for a period of time of six weeks and after Florida exposure in which the panels faced south at a 45 degree incline and were sprayed with a salt solution twice weekly. Results are set forth in Table 3 (mm creep). 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 3 
               
               
                   
               
               
                   
                 Horizontal 
                 Diagonal 
                   
                   
               
               
                   
                 6 weeks 
                 6 weeks 
                   
                   
               
               
                   
                 CETP  
                 CETP  
                 Florida 
                 Florida 
               
               
                 Example/Substrate 
                 L-467 
                 L-467 
                 3 months 
                 6 months 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 (cold-rolled steel) 
                 8.1 
                 6.1 
                 4.3 
                 10.2 
               
               
                 2 (cold-rolled steel) 
                 7.1 
                 6.0 
                 4.5 
                 10.6 
               
               
                 3 (cold-rolled steel) 
                 8.2 
                 6.6 
                 3.0 
                 7.5 
               
               
                 4 (cold-rolled steel) 
                 9.3 
                 5.7 
                 4.3 
                 10.6 
               
               
                 5 (cold-rolled steel) 
                 8.8 
                 6.2 
                 3.0 
                 7.4 
               
               
                 6 (cold-rolled steel) 
                 8.7 
                 5.4 
                 4.2 
                 10.8 
               
               
                 1 (electrogalvanized) 
                 2.0 
                 1.9 
                 0.8 
                 0.9 
               
               
                 2 (electrogalvanized) 
                 2.6 
                 1.8 
                 0.8 
                 1.2 
               
               
                 3 (electrogalvanized) 
                 2.1 
                 1.9 
                 1.1 
                 1.2 
               
               
                 4 (electrogalvanized) 
                 2.3 
                 1.5 
                 1.0 
                 1.0 
               
               
                 5 (electrogalvanized) 
                 2.5 
                 1.6 
                 0.8 
                 1.1 
               
               
                 6 (electrogalvanized) 
                 2.2 
                 2.1 
                 1.0 
                 1.1 
               
               
                 1 (hot-dipped galvanized) 
                 1.9 
                 2.1 
                 1.0 
                 1.1 
               
               
                 2 (hot-dipped galvanized) 
                 1.8 
                 1.3 
                 0.8 
                 1.2 
               
               
                 3 (hot-dipped galvanized) 
                 2.8 
                 1.7 
                 1.0 
                 1.1 
               
               
                 4 (hot-dipped galvanized) 
                 1.1 
                 1.5 
                 1.4 
                 1.4 
               
               
                 5 (hot-dipped galvanized) 
                 2.0 
                 1.7 
                 0.9 
                 1.0 
               
               
                 6 (hot-dipped galvanized) 
                 2.2 
                 1.7 
                 0.8 
                 1.0 
               
               
                 1 (aluminum alloy 6111) 
                 0.5 
                 0.5 
                 0.5 
                 0.5 
               
               
                 2 (aluminum alloy 6111) 
                 0.5 
                 0.5 
                 0.5 
                 0.5 
               
               
                 3 (aluminum alloy 6111) 
                 1.1 
                 0.6 
                 1.1 
                 1.1 
               
               
                 4 (aluminum alloy 6111) 
                 1.1 
                 0.9 
                 1.3 
                 1.4 
               
               
                 5 (aluminum alloy 6111) 
                 0.8 
                 0.5 
                 0.8 
                 1.3 
               
               
                 6 (aluminum alloy 6111) 
                 0.8 
                 0.5 
                 0.8 
                 1.7 
               
               
                   
               
            
           
         
       
     
     The coated panels were also tested for chip resistance according to Ford BI 157-06. Results are in Table 4 (Specification minimum rating is 6.0). 
     
       
         
           
               
               
               
             
               
                 TABLE 4 
               
               
                   
               
               
                   
                   
                 After 72 soak in  
               
               
                 Example/Substrate 
                 Initial 
                 deionized water 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 1 (cold-rolled steel) 
                 9.0 
                 7.3 
               
               
                 2 (cold-rolled steel) 
                 8.7 
                 7.3 
               
               
                 3 (cold-rolled steel) 
                 9.0 
                 7.3 
               
               
                 4 (cold-rolled steel) 
                 9.0 
                 7.0 
               
               
                 5 (cold-rolled steel) 
                 9.0 
                 7.7 
               
               
                 6 (cold-rolled steel) 
                 9.0 
                 8.0 
               
               
                 1 (electrogalvanized) 
                 9.0 
                 8.0 
               
               
                 2 (electrogalvanized) 
                 9.0 
                 8.0 
               
               
                 3 (electrogalvanized) 
                 9.0 
                 7.7 
               
               
                 4 (electrogalvanized) 
                 9.0 
                 7.7 
               
               
                 5 (electrogalvanized) 
                 9.0 
                 7.0 
               
               
                 6 (electrogalvanized) 
                 9.0 
                 8.0 
               
               
                 1 (hot-dipped galvanized)  
                 9.0 
                 8.0 
               
               
                 2 (hot-dipped galvanized) 
                 9.0 
                 7.7 
               
               
                 3 (hot-dipped galvanized) 
                 9.0 
                 8.0 
               
               
                 4 (hot-dipped galvanized) 
                 9.0 
                 8.0 
               
               
                 5 (hot-dipped galvanized) 
                 9.0 
                 8.0 
               
               
                 6 (hot-dipped galvanized) 
                 9.0 
                 8.0 
               
               
                 1 (aluminum alloy 6111) 
                 9.0 
                 8.0 
               
               
                 2 (aluminum alloy 6111) 
                 9.0 
                 8.0 
               
               
                 3 (aluminum alloy 6111) 
                 9.0 
                 8.0 
               
               
                 4 (aluminum alloy 6111) 
                 9.0 
                 8.0 
               
               
                 5 (aluminum alloy 6111) 
                 9.0 
                 8.0 
               
               
                 6 (aluminum alloy 6111) 
                 9.0 
                 8.0 
               
               
                   
               
            
           
         
       
     
     Examples 7-8: Sludge Analysis 
     Example 7 
     The following solutions were used in Example 7. Solutions A-D, F and H were as described in Example 1. Solution E was similar to Solution E of Examples 5 and 6. Solution E for Example 7 had 1160 ppm Zn, 320 ppm Ni, 850 ppm Mn, 0.8 ml free acid, 17.7 ml total acid, 260 ppm free fluoride, and 520 ppm total fluoride. Solution G for Example 7 was Chemseal 59 and had a pH of 4.6, 175 ppm total fluoride, 80 ppm Zr and 0 ppm Cu. 
     Example 8 
     The following solutions were used in Example 8. Solutions A-D, F and H were as described in Example 1. Solution E was similar to Solution E of Examples 3 and 4. Solution E for Example 8 had 960 ppm Zn, 365 ppm Ni, 877 ppm Mn, 0.8 ml free acid, 20.0 ml total acid, 124 ppm free fluoride, 284 ppm total fluoride and 10 ppm Zr. Solution G for Example 8 was similar to Solution G for Example 1 and had a pH of 4.8, 110 ppm free fluoride, 170 ppm Zr and 30 ppm Cu. 
     Examples 7 and 8: Test Results 
     After setting up these baths in 7.5 liter containers 30 40X6″ panels of various substrates were processed through the baths according to the process described in Table 2. The order they were processed in was as follows. 30 panels Al alloy 6022, 30 panels Al alloy 6111, 30 Cold-Rolled Steel panels, 30 Galvanneal panels, 30 Hot-Dipped Galvanized panels and 30 Electro-Galvanized panels were processed in that order and the suspended solids measured at the end of each run. Results are in Table 5. 
     
       
         
           
               
               
               
               
               
               
             
               
                 TABLE 5 
               
               
                   
               
               
                   
                   
                 Total 
                   
                   
                   
               
               
                 Run 
                   
                 Suspended 
                 Run 
                   
                 Total Suspended 
               
               
                 No. 
                 Bath 
                 Solids (ppm) 
                 No. 
                 Bath 
                 Solids (ppm) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 1 
                 Example 7, 
                 306 
                 1 
                 Example 8, 
                 277 
               
               
                   
                 Solution E 
                   
                   
                 Solution E 
                   
               
               
                 2 
                 Example 7, 
                 1332 
                 2 
                 Example 8, 
                 648 
               
               
                   
                 Solution E 
                   
                   
                 Solution E 
                   
               
               
                 3 
                 Example 7, 
                 1957 
                 3 
                 Example 8, 
                 896 
               
               
                   
                 Solution E 
                   
                   
                 Solution E 
                   
               
               
                 4 
                 Example 7, 
                 2099 
                 4 
                 Example 8, 
                 1451 
               
               
                   
                 Solution E 
                   
                   
                 Solution E 
                   
               
               
                 5 
                 Example 7, 
                 3339 
                 5 
                 Example 8, 
                 1316 
               
               
                   
                 Solution E 
                   
                   
                 Solution E 
                   
               
               
                 6 
                 Example 7, 
                 3345 
                 6 
                 Example 8, 
                 1126 
               
               
                   
                 Solution E 
                   
                   
                 Solution E 
                   
               
               
                 7 
                 Example 7, 
                 3855 
                 7 
                 Example 8, 
                 1013 
               
               
                   
                 Solution E 
                   
                   
                 Solution E 
               
               
                   
               
            
           
         
       
     
     The coating weights and etch rates are set forth in Table 6 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 6 
               
               
                   
               
             
            
               
                   
                   
                   
                 Etch Rate 
                 Coating Weight 
               
               
                 Run 
                 Substrate 
                 Bath 
                 [g/m2] 
                 [g/m2] 
               
               
                   
               
               
                 1 
                 CRS 
                 Example 7, Solution E 
                 1.1011 
                 3.3 
               
               
                 1 
                 HDG 
                 Example 7, Solution E 
                 0.6038 
                 2.4 
               
               
                 1 
                 GA 
                 Example 7, Solution E 
                 1.3013 
                 5.2 
               
               
                 1 
                 EG 
                 Example 7, Solution E 
                 0.9267 
                 2.8 
               
               
                 1 
                 Al6111 
                 Example 7, Solution E 
                 0.6167 
                 2.1 
               
               
                 1 
                 Al6022 
                 Example 7, Solution E 
                 0.7201 
                 1.8 
               
               
                 1 
                 CRS 
                 Example 8, Solution E 
                 0.5683 
                 2.9 
               
               
                 1 
                 HDG 
                 Example 8, Solution E 
                 0.8718 
                 2.9 
               
               
                 1 
                 GA 
                 Example 8, Solution E 
                 0.9558 
                 4.3 
               
               
                 1 
                 EG 
                 Example 8, Solution E 
                 0.6006 
                 3.0 
               
               
                 1 
                 Al6111 
                 Example 8, Solution E 
                 0.3132 
                 0.2 
               
               
                 1 
                 Al6022 
                 Example 8, Solution E 
                 0.2260 
                 0.2 
               
               
                 7 
                 CRS 
                 Example 7, Solution E 
                 0.6975 
                 3.3 
               
               
                 7 
                 HDG 
                 Example 7, Solution E 
                 0.4940 
                 3.3 
               
               
                 7 
                 GA 
                 Example 7, Solution E 
                 0.6652 
                 4.4 
               
               
                 7 
                 EG 
                 Example 7, Solution E 
                 0.4908 
                 3.5 
               
               
                 7 
                 Al6111 
                 Example 7, Solution E 
                 0.6716 
                 4.3 
               
               
                 7 
                 Al6022 
                 Example 7, Solution E 
                 0.6393 
                 3.8 
               
               
                   
               
               
                 Run 
                 Substrate 
                 Bath 
                 Etch [g/m2] 
                 CW [g/m2] 
               
               
                   
               
               
                 7 
                 CRS 
                 Example 8, Solution E 
                 0.7620 
                 3.1 
               
               
                 7 
                 HDG 
                 Example 8, Solution E 
                 0.6426 
                 3.1 
               
               
                 7 
                 GA 
                 Example 8, Solution E 
                 0.6297 
                 4.7 
               
               
                 7 
                 EG 
                 Example 8, Solution E 
                 0.7459 
                 3.3 
               
               
                 7 
                 Al6111 
                 Example 8, Solution E 
                 0.3552 
                 0.3 
               
               
                 7 
                 Al6022 
                 Example 8, Solution E 
                 0.3746 
                 0.2 
               
               
                   
               
            
           
         
       
     
     Corrosion Resistance 
     Examples 7 and 8 were tested for corrosion resistance. In the following, Example 7A is that same as Example 7 except that Solution G was omitted and Example 8A is the same as Example 8 except that Solution G was omitted. The panels were tested with two paint systems. Paint System #1 was as described above with respect to Examples 1-6 (ED6280Z electrocoat and topcoated using FCP6534 primer, UDCT 6466 basecoat, and TMAC8000 clearcoat). Paint System #2 was ED6107 electrocoat, PCV-70118primer, HWB83542 basecoat, and NCTXM clearcoat (all available from PPG Industries, Inc.) according to the manufacturers instructions. Results are set forth in Table 7. The results illustrate particular benefit of the present invention when an aluminum alloy having a relatively high copper content is used as part of the multi-metal assembly. 
     
       
         
           
               
               
               
               
             
               
                 TABLE 7 
               
               
                   
               
               
                   
                   
                   
                 ASTM G-85 Annex 2 
               
               
                 Pretreatment 
                   
                   
                 Avg scribe creep  
               
               
                 Set 
                 Paint System 
                 Substrate 
                 (mm) 6- weeks 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 Example 7 
                 Paint system 1  
                 Al6111 
                 8.1 
               
               
                 Example 7A 
                 Paint system 1 
                 Al6111 
                 6.8 
               
               
                 Example 8 
                 Paint system 1 
                 Al6111 
                 2.1 
               
               
                 Example 8A 
                 Paint system 1 
                 Al6111 
                 16.7 
               
               
                 Example 7 
                 Paint system 1 
                 Al6022 
                 1.4 
               
               
                 Example 7A 
                 Paint system 1 
                 Al6022 
                 2.0 
               
               
                 Example 8 
                 Paint system 1 
                 Al6022 
                 0.7 
               
               
                 Example 8A 
                 Paint system 1 
                 Al6022 
                 4.8 
               
               
                 Example 7 
                 Paint system 2 
                 Al6022 
                 1.8 
               
               
                 Example 7A 
                 Paint system 2  
                 Al6022 
                 2.7 
               
               
                 Example 8 
                 Paint system 2 
                 Al6022 
                 1.3 
               
               
                 Example 8A 
                 Paint system 2 
                 Al6022 
                 5.8 
               
               
                   
               
            
           
         
       
     
     It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it is intended to cover modifications which are within the spirit and scope of the invention, as defined by the appended claims.