METHOD FOR TREATING ALUMINUM CONTAINING SURFACES

Abstract: A primary film of Ni, Fe, and/or Co is formed on an aluminum surface and a phosphate film is formed on the aluminum surface on which this primary film has been formed, or on a composite of an aluminum surface on which a primary film has been formed and a zinc based coated steel sheet. This method of surface treatment is not accompanied with pollution problems with Cr<6+> ion and F<->, and there is little deterioration of the phosphate film forming treatment liquid with use.

Description: NETHOD FOR TREATING ALUMINUM CONTAINING SURFACES TECHNICAL FIELD This invention concerns a method of treating a surface including metallic aluminum or an aluminum alloy that is at least 45 % by weight, or preferably at least 85 % by weight, aluminum, in order to form on the surface a film which has excellent corrosion resistance, painting properties and electrodeposition painting properties. (Hereinafter, unless the context implies to the contrary, the term "aluminum" is to be understood as including aluminum alloys as specified above, and constitutions specified in percentages are to be understood as percentages by weight unless otherwise stated.) The process according to the invention is particularly suited to surfaces in sheet or strip form. In recent years, there has been a tendency to use aluminum sheet for parts of an automobile body in order to reduce the weight of automobiles. When this is done, the aluminum sheet or press formed aluminum sheet forms a composite material in which it is joined by welding, bonding or bolting to zinc alloy plated steel sheet, alloyed zinc plated steel sheet, zinc plated steel sheet, or the like. This present invention also concerns a method of forming films which have excellent corrosion resistance and painting properties on these composite materials. BACKGROUND ART In the past, phosphate treatment liquids which contained fluoride, especially in the form of silicofluoride, were used in the main for forming phosphate films on aluminum sheets and formed and worked aluminum sheets. However, there was a disadvantage in that there was a marked deterioration in the phosphate film forming properties due to the build-up of A13+ ion in the treatment liquid during the treatment for the formation of the phosphate film. Hence, with the conventional silicofluoride containing treatment liquids, renewal of the treatment liquid was required after a short period of time and there was a problem in that the cost of forming a phosphate film was high. Furthermore, the treatment liquids of which the forming properties for phosphate films had deteriorated were waste materials and there was a problem in that the disposal of the waste treatment liquids which contained fluoride was undesirable from the viewpoint of pollution. Acidic sodium fluoride and acidic potassium fluoride have been added to phosphate treatment liquids as a means of precipitating and removing the A13+ ion as K2NaAlF6 compounds in order to prevent the lowering of the forming properties due to the admixture of A13+ ions as mentioned above, but fluorine is contained in the precipitate and this is undesirable from the viewpoint of pollution. There are also methods in which a chromate film is formed on the aluminum sheet, for preventing the dissolution of aluminum into the phosphate treatment liquid, before the aluminum sheet is joined with a steel sheet, a zinc plated steel sheet or a zinc alloy plated steel sheet or the like and subjected to a phosphate treatment, but when these methods of treatment are used there are pollution problems with waste treatment liquids with Cr6+ and F and this is undesirable. DESCRIPTION OF THE INVENTION Problem to Be Solved bv the Invention This present invention takes as one of its objects the provision of a method for the formation of phosphate films with which the A13+ ion does not substantially increase in the phosphate treatment liquid and with which there is no deterioration of the phosphate film forming properties. Furthermore, this present invention discloses a method for the uniform formation of a phosphate film which has excellent corrosion resistance and painting properties on composite materials in which a press worked aluminum sheet and a steel sheet or a zinc based plated steel sheet are combined. Summary of the Invention In this present invention, a primary film of Ni, Fe or Co, or a composite of two or more of these, is formed on the aluminum sheet and washed with water. Pure aluminum and aluminum alloys of which aluminum is the principal component, for example pure aluminum such as 1S and 2S, corrosion resistant aluminum and magnesium based alloys such as 52S and 56S, aluminum and manganese based alloys such as 3S, aluminum and magnesium alloys such as 61S and 63S, duralumin such as 14S, 17S and 24S, and extra super duralumin such as 74S and 75S can be used for the aluminum sheet in this present invention. Hence, sheets of these aluminum materials are included among the aluminum sheets of this present invention. In this present invention, a primary film of Ni, Fe, Co is formed on these aluminum sheets. This primary film is obtained by coating Ni, Fe, Co on the aluminum sheet, preferably in an amount calculated as metal of 5 - 100 mg/m2 using a non-electrolytic or cathodic electrolytic method. This primary film can be formed using a simple method, as described hereinafter, and moreover it is not lost on cold forming and working or in the phosphate forming treatment and so it is desirable as a primary film. An example of a method of forming a primary film of Ni, Fe, Co or a compositie non-electrolytically is described below. First of all the aluminum sheet is degreased and washed, using alkali for example. For example, if the aluminum sheet is immersed for from 5 seconds to 2 minutes in a warm solution of 15 g/l of sodium carbonate, 25 g/l of sodium phosphate and surfactant, the oil and grease and the oxide film are removed from the aluminum sheet and a surface which is suitable for the deposition of Ni, Fe, Co or a combination thereof is obtained. The degreased and washed aluminum film is washed with water, neutralized with nitric acid, sulfuric acid or the like and washed with water. The treatment liquid for forming the primary film is an aqueous solution, used at a temperature in the range from normal ambient temperature to 800 C, which contains Fe2+, Fe3+, Ni2+, and/or Co2+, and, by immersing the degreased and washed aluminum sheet in this aqueous solution, or by spraying the aqueous solution onto the aluminum sheet, a primary film of Ni, Fe, and/or Co can be formed on the aluminum sheet. Alternatively, when the primary film is formed using a cathode electrolytic method, the aluminum sheet is immersed in an aqueous solution which contains Foe 2+ Foe3+ Ni2+, and/or Co2+ and a thin film is formed on the aluminum sheet, for example by cathode electrolysis at a current density of 0.3 - 30 amps/dm2 with a quantity of electricity of from 0.3 to 10 coulombs/dm2. For example, a solution in which from 20 to 50 grams of iron chloride or nickel chloride or cobalt chloride and 100 milliliters ("ml") of industrial hydrochloric acid have been dissolved in 1 liter of water can be used for the aqueous solution which contains Fe2+, Fe3+, Ni2+, and/or Co2+. Furthermore, nitrates, sulfates, phosphates and condensed phosphates are suitable, non-exclusive counterions for the aforementioned metal ions, and phosphoric acid, sulfuric acid, and nitric acid are suitable, non-exclusive acids for ajusting the acidity of the plating solution. The immersion time or cathode electrolysis time in the treatment liquid with which the primary film is formed is selected appropriately according to the composition of the aluminum sheet, but a metal primary film of Ni, Fe, and/or Co of some 5 - 100 mg/m2 is formed on the aluminum sheet by means of this procedure. The aluminum sheet is then washed with water and rinsed, whereupon an aluminum sheet on which a primary film of Ni, Fe or Co, or an alloy of two or more of these, is obtained as part of this present invention. A phosphate film is then formed on the aluminum sheet on which the primary film has been formed, using a treatment liquid which contains fluoride. Furthermore, when a phosphate film is formed on an aluminum sheet on which the primary film had been formed, the increase in A13+ ion in the treatment liquid is prevented and excellent phosphate film forming properties can be maintained over a long period of time. Furthermore, after the primary film has been formed on the aluminum sheet, the secondary phosphate film has been formed and an anti-rusting oil has been applied, the product can be obtained as a surface treated aluminum sheet. Furthermore, the primary film is not lost even if the aluminum sheet is press formed using the usual press lubricating oils, and it is retained on the aluminum sheet surface after press forming. Hence, aluminum sheet press worked and formed products with which the primary film is retained on the surface are obtained if a press lubricating oil is applied to an aluminum sheet on which a primary film has been formed and the sheet is then press formed and degreased, and when this formed product is subjected to a phosphate treatment the dissolution of aluminum into the phosphate treatment liquid which occurred in the past can be prevented and it is possible to form good phosphate films over long periods of time with no deterioration of the phosphate film forming properties of the treatment liquid. Furthermore, the inventors have made composite materials comprised of aluminum sheets and zinc plated steel sheets or plain steel sheets using aluminum sheets on which a primary film of Ni, Fe, and/or Co had been formed in an amount calculated as metal of 5 - 100 mg/m2, or an aluminum sheet obtained by press forming such a sheet, by joining with spot welding to the zinc based plated steel sheet or steel sheet. A phosphate film was formed on these composite materials using a phosphate film treatment liquid which contained fluorides of sodium and potassium, and good phosphate films could be formed on the aluminum sheet and on the zinc plated steel sheet or steel sheet. Furthermore, an attempt was made to form phosphate films on composites of aluminum sheet and zinc based plated steel or plain steel sheet using a treatment liquid which contained silicofluoride which had been used in the past when forming phosphate films on aluminum sheet and there was little dissolution of Al 3+ into the treatment liquid and good phosphate films could be formed on the aluminum sheet and the zinc based plated steel sheet or steel sheet. Brief Explanation of the Drawings Figure 1 is a drawing which shows the shape and size of the pressed formed product in Examples 2, and Figure 2 is an explanatory drawing of the bonded composite workpieces in example 3. Details of Some Preferred Embodiments of the Invention The invention may be further appreciated from the following examples and comparison examples. Examples 1.1 - 1.6 and ComParison Example 1.7 The inventors prepared in each case 100 aluminum sheets on which a primary film had been formed as shown in Table 1, using commercially pure aluminum sheet (Type 25) Table 1 AMOUNTS OF PRIMARY FILM AND CONDITIONS OF ITS FORMATION Example No. Primarv Film Formation Conditions and Amount Metal Con- Bath Tem- Contact Metal in Film, centration perature, Time in ms/m2 in Bath OC Seconds 1.1 3 g/L Ni+2 40 15 7 1.2 5 g/L Ni+2 45 30 23 1.3 5 g/L Fe+2 45 10 11 1.4 5 g/L Fe+2 60 90 + 3 g/L Fe+3 50 1.5 5 g/L Co+2 70 5 15 1.6 5 g/L Fe+2 + 5 g/L Ni 35 30 21 Ni + 13 Fe 1.7 --------No primary metal layer----------- Notes for Table 1 Test panels were initially degreased and cleaned by immersion for 5 minutes in a solution of FINECLEANERTM 315, comemrcially available from Nihon Parkerizing Co., Ltd., at a temperature of 55 - 60 C. Panels were then treated with 1 % aqueous hydrochloric acid solution as a neutralizing rinse before the treatments detailed above. with width of 300 mm, length of 300 mm, and thickness of 0.8 mm. These sheets were then subjected to the following process steps: De-grease and wash < water wash - neutralization rinse b water wash < primary film formation g wash - dry - anti-rusting oil coating - left to stand for 1 week indoors. The de-greasing washing, neutralization and primary film forming treatment conditions were as shown in table 1. After primary film formation as shown in Table 1, the samples were phosphated. A volume of 100 liters of the phosphate treatment liquid composition shown in Table 2, which contained silicofluoride, was housed in a treatment tank and the aforementioned aluminum sheets on which a primary film had been formed as shown in table 1 were de-greased and washed with water and then immersed for 2.0 minutes/ sheet successively, using 50 sheets one after the other, in the phosphate treatment liquid, so that a phosphate film was formed. The phosphate film formation results are shown in Table 3. Table 2 COMPOSITION OF PHOSPHATING SOLUTION FOR (COMPARISON) EXAMPLES 1 Zn2+ Concentration : 1.5 g/l 3- PO43- Concentration : 15 g/l NO3 Concentration : 8 g/l Ni2+ Concentration : 1.5 g/l NO2 Concentration : 0.1 g/l Six62 Concentration : 1.0 g/l Note for Table 2 The phosphating solution was used at a temperature of 430 C. Table 3 RESULTS OF PHOSPHATING IN (COMPARISON) EXAMPLES 1 Example No. Results for: Twentieth Sheet Fiftieth Sheet Areal Dens- Concen- Areal Dens- Concen sity of tration sity of tration Phosphate of Al Phosphate of Al Film. s/m2 Ions in Film, a/rn Ions in Treat- Treat ment ment Liauid Liauid 1.1 1.9 14 1.5 33 1.2 2.0 9 2.0 18 1.3 1.9 11 1.7 25 1.4 1.8 13 1.4 30 1.5 2.3 8 1.8 30 1.6 2.2 7 2.1 16 1.7 1.5 27 0.2 48 Notes for Table 3 The samples were also subjected to a Filiform Corrosion Promotion Test Method, as follows: A specimen in which scratches had been made in a cationically electrodeposited paint film surface were immersed for 2 hours in 0.5N HCl aqueous solution which contained 1% H2O2 at 300C and then washed with water and dried. Then, they were left to stand for 240 hours in a room at 400C and 85% relative humidity. and an assessment was made after six of these cycles. The filiform corrosion length was less than 5 mm for Experiments 1. 1 and 1.4, 5 - 10 mm for the remaining Experiments 1.2, 1.3, 1.5, and 1.6, and more than 11 mm for Comparison Experiment 1.7. The aluminum ion concentrations are given in parts per million by weight. It is clear from Table 3 that in all cases where an aluminum sheet on which a primary film had been formed was used, a phosphate film of adequate thickness was formed in a stable manner and, furthermore, as shown in the filiform corrosion propagation test results column in table 3, phosphate films which had excellent performance can be formed. Furthermore, even when 50 sheets were treated successively the concentration of Al 3+ ion in the phosphate treatment liquid was low and there was little or no deterioration in the coating forming power of the phosphate treatment liquid. However, as shown by the comparative example in Table 3, when an aluminum sheet on which no primary film had been formed was used, the Al 3+ ion concentration in the phosphate treatment liquid increased on treating about 20 sheets and the phosphate film forming power deteriorated. Consequently, the phosphate film became successively thinner after the twentieth sheet and by the fiftieth sheet essentially no phosphate film at all could be formed with an immersion time of 2.0 minutes/sheet. Examples 2.1 - 2.6 Ten of each of the aluminum sheets on which a primary film had been formed, using the same method as in Experiments 1.1 - 1.6 respectively, were press formed using the process outlined below and the formed products were treated with a phosphate film treatment liquid as shown in Table 2. The process step sequence was: aluminum sheet on which a primary film had been formed g coating with lubricating oil < press forming < degreasing washing b water washing < phosphate film forming treatment t water washing The lubricating oil coating and degreasing washing treatment conditions were as follows: Lubrication Oil Coating: NOX-RUST550HNTM (made by Parker Kosan Co.) was applied by coating with a brush. Degreasing Washing: Immersed for 2.0 minutes in an aqueous solution of FINECLEANERTM L4460 (made by Nihon Parkerizing Co.) Furthermore, the press forming was carried out with deep cylindrical pressing as shown in figure 1. Also, the phosphate film forming treatment was carried out with the same immersion time (2.0 minutes/ sheet) using the same treatment liquid as in table 2. The results of phosphate film formation were as shown in Table 4. As shown in Table 4, the aluminum sheets on which a primary film of this invention had been formed and which had been press formed were such that a phosphate film could be formed in roughly the same way as with aluminum sheets which had not been subjected to press forming, as described in Table 3. Table 4 RESULTS FROM PHOSPHATING PRESS FORMED PRIMARY METAL COATED SHEETS ACCORDING TO THIS INVENTION Example No. Weight of Phosphate A13+ Ion Concentration Film on l0t2h Sheet in Treatment Liquid in g/m at 10th Sheet in pDm 2.1 2.0 7 2.2 2.1 5 2.3 2.1 6 2.4 2.0 7 2.5 2.4 5 2.6 2.3 4 Examples 3.1 - 3.6 Seams were formed by spot welding, at five points as shown in Figure 2, a cold rolled steel sheet with a width of 300 mm, length of 300 mm and thickness of 0.7 mm to each of the aluminum sheets on which a primary film had been formed using the same methods as in Examples 1.1 - 1.6 respectively, and the resulting materials were treated in a phosphate film treatment liquid. The treatment liquid shown in Table 2 was used for the phosphate film forming liquid and in each case the material was immersed for 2.0 minutes. The results of phosphate film formation were as shown in Table 5. It is clear from Table 5 that good phosphate films were formed on the aluminum sheet and the cold rolled steel sheet. Seams were formed by spot welding formed hot dip galvanized steel sheets which had been press formed and worked, instead of the cold rolled steel sheet as noted in the preceding paragraph, onto aluminum sheet on which a primary film had been formed and a phosphate film forming treatment was carried out using the same procedure, and in this case again a good phosphate film was formed on the zinc plated steel sheet and the aluminum sheet. Table 5 PHODSPHATE FILM WEIGHTS FOR SOME COMPOSITE SUBSTRATES Example No. Phosphate Film Weiaht in s/m2 on: Aluminum Sheet Cold Rolled Steel Sheet 3.1 2.1 2.2 3.2 2.2 2.2 3.3 2.1 2.2 3.4 2.0 2.3 3.5 2.4 2.2 3.6 2.3 2.2 Benefits of the Invention As has been described above, when the invention is employed a phosphate film which has excellent corrosion resistance and painting properties is formed uniformly, in a state in which the dissolution of aluminum into the phosphate treatment liquid is suppressed, on an aluminum surface or a composite in which an aluminum surface, which may be press worked, is combined with a steel or a galvanized steel surface, which may or may not have been press worked.

Claims: CLAIMS 1. A process for protectively coating a metallic surface, said metallic surface comprising areas of aluminum or an alloy thereof and optionally also comprising areas of steel, galvanized steel, or both, said process comprising steps of: (A) forming on the metallic surfaces a primary film of metal consisting of metals selected from the group consisting of nickel, iron, cobalt, and mixtures thereof; (B) contacting the primary film formed in step (A) with water; and (C) applying a phosphate conversion coating to the primary film coated surface that has been contacted with water in step (B). 2. A process according to claim 1, wherein the shape of the aluminum or aluminum alloy part of the protectively coated metallic surface has been mechanically altered between steps (A) and (C). 3. A process according to claim 2, wherein the protectively coated surface includes areas of steel or galvanized steel and the shape of these areas has been mechanically altered between steps (A) and (C). 4. A process according to claim 1, wherein the protectively coated surface includes areas of steel or galvanized steel and the shape of these areas has been mechanically altered between steps (A) and (C). 5. A process according to claim 4, wherein the primary film has an areal density of from 5 to 100 mg/m2 calculated as metal. 6. A process according to claim 3, wherein the primary film has an areal density of from 5 to 100 mg/m2 calculated as metal. 7. A process according to claim 2, wherein the primary film has an areal density of from 5 to 100 mg/m2 calculated as metal. 8. A process according to claim 1, wherein the primary film has an areal density of from 5 to 100 mg/m2 calculated as metal. 9. A process according to any of claims 1 - 8, wherein the phosphate conversion coating has an areal density of at least 1.4 g/m2. 10. A process according to claim 9, comprsing additional steps of alkaline cleaning the protectively coated metal surface and subsequently neutralizingly rinsing it before step (A) and a degreasing step between steps (A) and (B), and wherein a composition containing at least 0.5 g/L of -2 SiF6 2 ions is used to apply the phosphate conversion coating in step (C).

Inventors: MATSUSHIMA YASUNOBU, TANAKA SHIGEO, TANI DAIJIRO, MATSUSHIMA, YASUNOBU, TANAKA, SHIGEO, TANI, DAIJIRO
Applicants: HENKEL CORP, HENKEL CORPORATION
Application year: 1991
Main classification: C23C22
IPC codes: C23C22