Patent Publication Number: US-2022213612-A1

Title: Anodized coating for magnesium

Description:
RELATED APPLICATION INFORMATION 
     This application claims the benefit of U.S. Provisional Application No. 62/827,502, filed Apr. 1, 2019, the contents of which are fully incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates generally to anodized coatings for magnesium, and more particularly to anodized coatings and coating processes that incorporate additives to further improve physical attributes of the coating. 
     BACKGROUND 
     Anodizing magnesium for the purpose of providing improved protection against corrosion has been carried out for several decades. Beginning in the mid-1940s, the Dow Chemical Company developed the first commercially applicable anodized magnesium coatings. One of the more popular coatings was referred to as the Dow 17 coating. The Dow 17 coating was applied by immersing a magnesium component in an electrolyte of sodium dichromate, ammonium acid fluoride and phosphoric acid while applying an electrical current. The process produced a natural oxide layer over the component having a generally greenish appearance with a thickness of between about 0.2 and 0.3 mil. 
     In 1952, another type of anodized coating, commonly referred to as an HAE coating, was developed by Harry A. Evangelides. The HAE coating was applied by immersing a magnesium component in an electrolyte of potassium permanganate, potassium chloride, trisodium phosphate, potassium hydroxide, and aluminum hydroxide, while applying an alternating current. Like the Dow 17 coating, the process produced a natural oxide layer over the component with a thickness of generally between about 0.2 and 0.3 mil. However, instead of a generally greenish appearance like the Dow 17 coating, the HAE coating had a generally brownish appearance. 
     Although both anodized coatings generally served to protect the magnesium surface and provide improved paint adhesion, both coatings had a very porous structure, and therefore were susceptible to corrosion over extended periods of time. Moreover, in the early 1990s, health, safety and environmental legislation (e.g., the Clean Air Act Amendments of 1990 and enforcement of the Clean Water Act) demanded more environmentally friendly magnesium coatings; particularly, coatings that were free of chromium and other heavy metals, such as manganese. 
     With such legislation in mind, Assignee of the present patent application developed an anodized coating process, commonly referred to as the Tagnite™ coating, as a replacement for the Dow 17 and HAE coatings. The Tagnite™ coating is produced by an electrochemical process during which magnesium oxide is grown on the surface of the magnesium component through an anodization process. Exemplary embodiments of the Tagnite™ coating process are described in U.S. Pat. Nos. 5,264,113; 5,240,589; 5,266,412; and 5,470,664 the disclosures of which are hereby incorporated herein by reference in their entirety. Unlike the Dow 17 and HAE coatings, the Tagnite™ coating does not utilize chromium or other heavy metals. 
     Although the resultant Tagnite™ coating generally exhibits improved physical attributes (e.g., improved hardness and corrosion resistance) over the Dow 17 and HAE coatings, further improvements to physical attributes of the Tagnite™ coating, such as improvements to abrasion resistance, surface lubricity, color, and conductivity, are desirable. The present disclosure addresses these concerns. 
     SUMMARY OF THE DISCLOSURE 
     Embodiments of the present disclosure provide anodized coatings and coating processes that incorporate one or more physical property modifying additives within a magnesium oxide layer during the growth of the magnesium oxide layer for the purpose of improving or altering hardness, abrasion resistance, surface lubricity, color and/or electrical conductivity. 
     One embodiment of the present disclosure provides a method of producing an anodized coating on a magnesium containing article, including: mixing a chemical slurry including a quantity of an aqueous soluble hydroxide, a fluoride composition, at least one of silicate or vanadate, and between about 5 g/L and about 150 g/L of at least one physical property modifying agent; immersing a magnesium containing article in the chemical slurry; and applying at least one of an electrical current or electrical potential to the magnesium containing article to promote a chemical reaction on a surface of the magnesium containing article resulting in the growth of a porous magnesium oxide layer on a surface of the magnesium containing article containing at least elements of the one or more physical property modifying agents. 
     In one embodiment, the at least one physical property modifying agent can be zinc oxide. In one embodiment, the zinc oxide added to the chemical slurry can have at least one of a particle size of between about 10 μm and about 100 μm, or a particle size of between about 10 nm and about 100 nm. In one embodiment, the zinc oxide can be added to the chemical slurry in an amount of about 14 g/L or more. In one embodiment, the zinc oxide can be added to the chemical slurry in an amount of about 35 g/L or more. In one embodiment, elements of the one or more physical property modifying agents can be more highly concentrated in structure surrounding pores of the magnesium oxide layer. In one embodiment, the magnesium containing article can exhibit at least one of improved hardness or abrasion resistance after growth of the porous magnesium oxide layer. 
     In one embodiment, the at least one physical property modifying agent can be at least one of diamond particles, garnet particles, silicon carbide, aluminum oxide, Teflon™ particles, or molybdenum disulfide. In one embodiment, at least one physical property modifying agent can be in the form of a crystal. In one embodiment, at least one physical property modifying agent can have a particle size of less than one-fifth of an average pore size of the porous magnesium oxide layer. In one embodiment, the magnesium containing article can exhibit an alteration of at least one of a hardness, abrasion resistance, surface lubricity, color, and/or electrical conductivity of the magnesium oxide layer. 
     Another embodiment of the present disclosure provides an anodized coating method including growing a porous magnesium oxide layer on a surface of a magnesium containing article, wherein the porous magnesium oxide layer includes concentrations of zinc surrounding structure defining pores of the magnesium oxide layer. 
     Yet another embodiment of the present disclosure provides a magnesium containing article having an abrasion resistant anodized coating. The magnesium containing article can include a magnesium containing substrate, and a porous magnesium oxide growth layer on the surface of the magnesium containing substrate including concentrations of zinc in structure surrounding pores of the magnesium oxide layer. 
     The summary above is not intended to describe each illustrated embodiment or every implementation of the present disclosure. The figures and the detailed description that follow more particularly exemplify these embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure can be more completely understood in consideration of the following detailed description of various embodiments of the disclosure, in connection with the accompanying drawings, in which: 
         FIG. 1  is a schematic diagram depicting a system for carrying out an anodized coating for magnesium, in accordance with an embodiment of the disclosure. 
         FIG. 2  is a flowchart depicting an anodized coating process, in accordance with an embodiment of the disclosure. 
         FIG. 3A  depicts a top view of a sample anodized coating at 5000× magnification, in accordance with an embodiment of the disclosure. 
         FIG. 3B  depicts an elemental mapping view of the sample anodized coating of  FIG. 3A , in which concentrations of both zinc and silicate are highlighted. 
         FIG. 3C  depicts an elemental mapping view of the sample anodized coating of  FIG. 3A , in which concentrations of zinc are highlighted. 
         FIG. 3D  depicts an elemental mapping view of the sample anodized coating of  FIG. 3A , in which concentrations of silicate are highlighted. 
         FIG. 4A  depicts a profile view of a sample anodized coating at 5000× magnification, in accordance with an embodiment of the disclosure. 
         FIG. 4B  depicts an elemental mapping view of the sample anodized coating of  FIG. 4A , in which concentrations of both zinc and silicate are highlighted. 
         FIG. 4C  depicts an elemental mapping view of the sample anodized coating of  FIG. 4A , in which concentrations of zinc are highlighted. 
         FIG. 4D  depicts an elemental mapping view of the sample anodized coating of  FIG. 4A , in which concentrations of silicate are highlighted. 
         FIG. 5  is a line graph depicting a measured cumulative weight loss of a control sample and two test samples over the course of abrasion analysis, in accordance with an embodiment of the disclosure. 
         FIG. 6  is a bar graph depicting a measured cumulative weight loss of a control sample and three test samples over the course of abrasion analysis, in accordance with an embodiment of the disclosure. 
         FIG. 7A  depicts a sample magnesium containing article having an anodized coating incorporating one or more physical property modifying agents, in accordance with an embodiment of the disclosure. 
         FIG. 7B  depicts a close-up view through an electron microscope of one area of the sample magnesium containing article depicted in  FIG. 4A  that was subjected to abrasion analysis, in accordance with an embodiment of the disclosure. 
     
    
    
     While embodiments of the disclosure are amenable to various modifications and alternative forms, specifics thereof shown by way of example in the drawings will be described in detail. It should be understood, however, that the intention is not to limit the disclosure to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the subject matter as defined by the claims. 
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , a system  100  for carrying out an anodized coating of magnesium is depicted in accordance with an embodiment of the disclosure. The system  100  can generally include an electrochemical bath  102  containing a chemical slurry  104  into which a magnesium containing article  106  can be immersed to affect an anodized coating. The term “magnesium containing article,” as used herein, refers to a metallic article or component having a magnesium or magnesium alloy surface. In one embodiment, the article is a manufactured component (e.g., sand cast, die cast, extruded, forged, and/or machined) comprising a magnesium rich alloy containing at least about 50 wt-% magnesium. In one embodiment, the article includes one or more layers of metal, in which a magnesium or magnesium alloy surface is exposed. 
     Prior to the anodized coating, the magnesium containing article  106  can optionally be pretreated to degrease or cleanse the surface of the magnesium containing article  106  and/or to create a desirable base over at least a portion of the surface of the magnesium containing article  106 . In other embodiments, the magnesium containing article  106  can be immersed in the chemical slurry  104  without preconditioning. 
     While immersed in the slurry  104 , an electrical potential and/or current can be applied to the magnesium containing article  106  via a rectifier  108 . In one embodiment, the rectifier  108 , which can be in electrical communication with a voltage source  110 , can be configured to produce a wave signal configured to drive the anodized coating process. In one embodiment, the rectifier  108  can have an output voltage potential of between about 150 volts and about 360 volts; although other output voltages of the rectifier  108  are also contemplated. 
     To apply the electrical potential and/or current across the magnesium containing article  106 , an anode  112  in electrical communication with the rectifier  108  can be placed in electrical communication with the magnesium containing article  106  (such that the article  106  effectively becomes the anode  112 ). A cathode  114 , also in electrical communication with the rectifier  108  can be placed elsewhere within the chemical slurry  104 , so as to create an electrical potential between the cathode  114  and the magnesium containing article  106  through at least a portion of the slurry  104 , such that the magnesium containing article  106  generally has a positive charge. In another configuration, the position of the anode  112  and the cathode  114  can be reversed, such that the magnesium containing article  106  generally has a negative charge. 
     During the anodized coating process, the slurry  104  can be agitated or circulated within the electrochemical bath  102 , such that the slurry  104  (which can be a heterogeneous mixture) remains in suspension. In one embodiment, a magnetic stir plate can be utilized to agitate the slurry  104  within the electrochemical bath  102 . In other embodiments, the slurry  104  can be circulated via a pump  116 . Such a configuration can be particularly useful where certain components of the slurry  104  tend to settle at the bottom of the electrochemical bath  102  during the anodized coating process. Accordingly, the pump  116  can continuously pull a quantity of slurry  104  through one or more outlets or drains  118  and reintroduce the quantity of slurry  104  into the electrochemical bath  102  through one or more inlets or jets  120 , thereby inhibiting separation of the slurry  104 . In one embodiment, the pump  116  can serve to pressurize the slurry  104 , such that reintroduction of the slurry  104  into the electrochemical bath  102  occurs under force. In one embodiment, the one or more inlets  120  can be formed as nozzles configured to improve agitation and overall mixing of the slurry  104 . 
     In one embodiment, the pump  116  can further be configured to route the quantity of slurry  104  through a heat exchanger  122 , which can be in communication with a heat sump  124 . The heat exchanger  122  and heat sump  124  can be configured to maintain the slurry at a desired temperature, or at least partially control or slow a natural increase in the slurry  104  temperature during the anodized coating process. For example, in one embodiment, the slurry  104  can be maintained at a temperature of between about 2° C. and about 30° C. over the course of the anodized coating process; although other temperatures of the slurry  104  are also contemplated. In an alternative embodiment, a heat exchanger or chiller (for example in the form of a coil) can be positioned directly within the electrochemical bath  102 ; particularly where a magnetic stir plate is utilized to agitate the slurry  104 . 
     The slurry  104  can be formed of an aqueous electrolytic solution having a pH of at least 12.5, and comprising between about 2 g/L and about 12 g/L of an aqueous soluble hydroxide, between about 2 g/L and about 15 g/L of a fluoride containing composition selected from the group consisting of fluorides and fluorosilicates, and between about 5 g/L and about 30 g/L of silicate or vanadate. 
     In one embodiment, one or more physical property modifying agents can be added to the slurry  104 . The one or more physical property modifying agents can be configured to improve surface hardness, increase surface lubricity, modify a surface color, increase electrical conductivity, and the like. For example, in one embodiment, a physical property modifying agent, such as zinc oxide (ZnO), can be added to the slurry  104  to increase the surface hardness and improve abrasion resistance of the magnesium containing article  106 . Other physical property modifying agents include: micro-sized industrial diamond particles (e.g., particles of C having a size of between about 0.1 and about 100 μm), nano-sized industrial garnet particles (e.g., particles of A 3 B 2 Si 3 O 12  having a size of between about 1 nm and about 100 nm), silicon carbide (SiC), aluminum oxide (Al 2 O 3 ), micro-sized polytetrafluoroethylene (e.g., Teflon™) Teflon™ spheres ((C 2 F 4 ) n ), and a solid lubricant (e.g., molybdenum disulfide (MoS 2 )), all of which can be added to the slurry  104  either alone or in combination, to improve physical attributes of the anodized coating. In one embodiment, the one or more physical property modifying agents can be added to the slurry  104  in the amount of between about 1 g/L and about 150 g/L. 
     Referring to  FIG. 2 , a flowchart illustrating an anodized coating process  200  is depicted in accordance with an embodiment of the disclosure. At  202 , an untreated magnesium containing article  106  can optionally be pretreated to clean the surface of the article  106  and/or to form a fluoride containing layer over at least a portion of the surface of the article  106 . A pretreatment chemical bath of an aqueous ammonium fluoride solution can be prepared for the optional pretreatment. In some embodiments, the pretreatment chemical bath can comprise between about 0.2 and about 5 molar aluminum fluoride in water, having a pH of between about 4 and about 8, and a temperature of between about 40° C. and about 100° C. 
     The magnesium containing article  106  can be maintained in the pretreatment chemical bath for a time sufficient to clean impurities at the surface of the article  106  and to form a fluoride containing base layer having a thickness of between about several hundred Angstroms and greater than about 1000 Ångstroms. For example, in one embodiment, the magnesium containing article  106  can be immersed in the pretreatment chemical bath for between about 15 minutes and about 180 minutes; although, it is noted that pretreatment chemical baths on the lower end of the pH spectrum and on the higher end of the temperature spectrum may result in faster oxidation and/or etching reaction rates. 
     Upon emerging from the pretreatment chemical bath, the magnesium containing article  106  is predominately coated with metal fluoride base layer containing small amounts metal oxide and/or metal oxofluoride, most of the metal being magnesium depending on the nature of the alloy. The base layer is generally uniform in composition and thickness across the surface of the article  106  and provides an excellent base upon which a ceramic-like anodized coating layer can be formed. Although pretreatment of the magnesium containing article  106  is optional, it has been found that pretreatment enhances corrosion and abrasion resistance, as the base layer promotes better adhesion between the article  106  and the anodized coating layer. Where pretreatment is utilized, at  204 , the article  106  can optionally be washed with a water solution to remove any unreacted ammonia fluoride, as well as to inhibit contamination of the chemical slurry  104  with remnants of the pretreatment chemical bath. 
     At  206 , the magnesium containing article  106  can be immersed in an electrochemical bath  102  containing a chemical slurry  104  (such as that depicted in  FIG. 1 ). Exemplary composition ranges for the chemical slurry  104  are shown below in table I. 
     
       
         
           
               
               
             
               
                 TABLE I 
               
               
                   
               
               
                 Component 
                 Quantity Range 
               
               
                   
               
             
            
               
                 Hydroxide 
                 between about 2 g/L and about 12 g/L 
               
               
                 Fluoride 
                 between about 2 g/L and about 15 g/L 
               
               
                 Silicate AND/OR Vanadate 
                 between about 5 g/L and about 30 g/L 
               
               
                 One or More Physical Property 
                 between about 5 g/L and about 150 g/L 
               
               
                 Modifying Agents 
               
               
                   
               
            
           
         
       
     
     In one embodiment, the aqueous soluble hydroxide can be an alkali metal hydroxide, for example, lithium, sodium, potassium, and/or potassium hydroxide. In one embodiment, the fluoride containing composition can be an alkali metal fluoride, such as lithium, sodium and potassium fluoride, and/or an acid fluoride such as hydrogen fluoride or ammonium bifluoride. Fluorosilicates such as potassium fluorosilicates can also be used. In one embodiment, the fluoride containing compound comprises an alkali metal fluoride, an alkali metal fluorosilicate, hydrogen fluoride, or mixtures thereof. In one embodiment, the fluoride containing compound comprises potassium fluoride. In one embodiment, the silicate can be an alkali metal silicate, an alkali metal fluorosilicate, and/or can comprise lithium, sodium and/or potassium silicate. The one or more physical modifying agents can include aluminum oxide, diamonds, garnets, silicon carbide, Teflon™, and molybdenum disulfide, among others. 
     At  208 , while the magnesium containing article  106  is immersed in the slurry  104 , an electrical potential can be applied. In one embodiment, the magnesium containing article  106 , which is in electrical communication with the rectifier  108 , can serve as an anode  112 . A portion of the electrochemical bath  102 , which is also in electrical communication with the rectifier, can serve as the cathode  114 . The rectifier  108  rectifies a voltage from a voltage source  110  to provide a current density to the electrochemical bath  102 , thereby driving the chemical reaction. 
     Example conditions of the chemical slurry  104  are shown below in table II. 
     
       
         
           
               
               
             
               
                 TABLE II 
               
               
                   
               
               
                 Component 
                 Range 
               
               
                   
               
             
            
               
                 Alkalinity 
                 between about 12 pH and about 14 pH 
               
               
                 Temperature 
                 between about 2° C. and about 30° C. 
               
               
                 Current Density 
                 between about 2 mA/cm 2  and about 90 mA/cm 2   
               
               
                   
               
            
           
         
       
     
     Typically the magnesium containing article  106  is immersed in the slurry  104  for a period of between about 5 minutes and about 80 minutes. After between about 10 minutes and about 30 minutes, the reaction on the surface of the article  106  forms of a ceramic-like anodized coating having a thickness of between about 10 μm (0.39 mil) and about 30 μm (1.18 mil). Although the rate of reaction slows with increasing time, maintaining the article  106  within the slurry  104  for longer periods of time can result in a thicker anodized coating. For example, after about 80 minutes the anodized coating can have a thickness of greater than about 40 μm (1.57 mil). In most applications, the anodized coating is applied in a thickness of between about 0.1 mil and about 0.9 mil, depending upon the alloy and the intended application of the article  106 . 
     It should be understood that the individual steps used in the methods of the present teachings may be performed in any order and/or simultaneously, as long as the teaching remains operable. Furthermore, it should be understood that the apparatus and methods of the present teachings can include any number, or all, of the described embodiments, as long as the teaching remains operable. 
     Accordingly, the above described anodized coating process  200  results in growth of an irregular porous ceramic-like magnesium oxide layer over the surface of the magnesium containing article  106 . The magnesium oxide layer is primarily composed of magnesium, silicate or vanadate, and optionally zinc or one or more other physical property modifying agents. 
     The addition of zinc oxide as a physical property modifying agent can be used to increase the surface hardness and to improve wear characteristics of the magnesium containing article. For example, in some embodiments, between about 5 g/L and about 150 g/L of zinc oxide microparticles (e.g., particles having a size of between about 10 μm and about 100 μm) can be added to the slurry  104 . In other embodiments, zinc oxide nanoparticles (e.g., particles having a size of between about 10 nm and about 100 nm) can be utilized. During growth of the anodized layer, zinc from the zinc oxide becomes integrated within the anodized coating, with a particular concentration in the grooves, angles and ridges defined by the porous structure of the magnesium oxide layer, thereby resulting in an anodized coating including a higher concentration of zinc than may be present in other portions of the magnesium containing article  106 , even where the magnesium containing article  106  is constructed of a magnesium alloy containing zinc. Further, whereas the conventional Tagnite™ coating generally presents a whitish appearance, the incorporation of zinc oxide within the slurry  104  causes a chemical reaction during the deposition process resulting in an anodized coating having a gray/tan appearance. 
     Initial testing of anodized coatings with the use of zinc oxide as a physical property modifying agent has indicated abrasion resistances between about 2-3 times greater than anodized coatings without the use of zinc oxide as an additive. Accordingly, anodized coatings incorporating zinc oxide as disclosed herein are ideal for magnesium containing articles  106  subjected to abrasion over the course of their lifetime, for example mechanical components subjected to sliding and/or rotational contact with an abrading surface, such as another mechanical component (possibly constructed of another material) during use. Commercial applications of anodized coatings can be used in the automotive, aerospace, firearm, sporting-goods, power tool, consumer electronics, and internal combustion engine industries; although the use of anodized coatings that incorporate additives to further improve physical properties and/or characteristics of the magnesium containing article  106  across other industries and applications are also contemplated. 
     Other physical property modifying agents, which can be added to the slurry  104  in addition to zinc oxide, or in place of zinc oxide, can include micro-sized diamond particles, nano-sized garnet particles, silicon carbide, and/or aluminum oxide, each of which generally serves to increase the surface hardness and to improve service lubricity of the magnesium containing article  106 . For example, in one embodiment, the physical modifying property agents can be in the form of crystals captured or frozen as discrete particles within the grooves, angles and ridges of the porous magnesium oxide layer. In one embodiment, the physical property modifying agents can have a particle size between about ½ and about 1/20 of the average pore size of the magnesium oxide layer, thereby inhibiting interference between the presence of the physical property modifying agents and the natural porosity of the magnesium oxide layer. In some embodiments, the one or more physical property agents can be entrapped throughout the thickness of the porous magnesium oxide layer, such that as portions of the magnesium oxide layer are worn away through abrasion, more physical property modifying agents become exposed to the surface. 
     Other physical property modifying agents such as micro-sized Teflon™ spheres and solid lubricants, such as molybdenum disulfide, can be utilized to increase the surface lubricity of the magnesium containing article  106 , thereby decreasing the frictional resistance and resultant abrasive wear during the sliding and/or rotational contact with an opposing surface. In cases where electrical conductivity or insulating properties of the article are desired, various physical property modifying agents configured to affect the electrical conductivity of the anodized coating can be added to the slurry. In embodiments, the one or more physical property modifying agents can be chemically compatible with the slurry  104  with generally electrically nonconductive of properties, so as to inhibit a short circuit between the anode  112  and the cathode  114 . 
     In one embodiment one or more color enhancing agents can be added to the slurry  104  to adjust or alter the color of the anodized coating to produce an anodized coating having a colored appearance other than the typical whitish appearance. For example, in one embodiment, the one or more color enhancing agents can be configured to produce a black, gray, tan, brown, or olive drab colored appearance. Although, other colors such as pink, red, orange, yellow, green, blue, indigo, violet, and combinations thereof are also contemplated. In some embodiments, the anodized coating can serve as a primer base offering excellent adhesion for an optional finishing coat, such as paint. In other embodiments, the anodized coating itself can serve as the finished coat. In some embodiments, the physical property modifying agent can be configured to participate in a color changing reaction after completion of the anodized coating, so as to affect a post-process coloring of the article. 
     EXAMPLES 
     The following specific examples can be used to further illustrate the disclosed embodiments. These examples are merely illustrative and are not intended to limit the scope of the claimed invention. 
     Samples X1-X2 
     In one study of the anodized coating process  200 , two AZ31B magnesium panels were given anodized coatings in which zinc oxide particles were added to the slurry  104 , with the intent of enhancing the hardness and abrasion resistance of the test panels. In particular, the first sample (X1) was immersed in a slurry comprising 1.1 g/L of zinc oxide microparticles, and the second sample (X2) was immersed in a slurry comprising 45.4 g/L of zinc oxide nanoparticles. 
     Referring to  FIGS. 3A and 4A , respective top and profile views of the anodized coating  300  of X1 at 5000× magnification is depicted in accordance with an embodiment of the disclosure. As can be seen, granular zinc particles  302  are incorporated into the porous structure of the anodized coating  300 , with particular concentration of zinc  302  in the grooves, angles and ridges defined by the porous structure of the magnesium oxide layer. During the deposition process, it is believed that the sharp corners of the grooves, angles and ridges cause ionized zinc to migrate to these areas. Accordingly, although zinc  302  is embedded throughout the skeleton of the oxide layer coating  300 , the presence of zinc tends to be in highest concentrations in the structure surrounding the pores. Concentration of the elements within the porous structure of the anodized coating can be further seen in  FIGS. 3B-D  and  4 B-D, which depict elemental mapping of sample X1 at 5000× magnification. In particular, the distribution of zinc throughout the anodized coating is highlighted in  FIGS. 3C &amp; 4C , while the distribution of silicate is highlighted in  FIGS. 3D &amp; 4D . 
     Upon completion of the coating process the control sample and test samples were subjected to a Taber abrasion analysis is defined by 3LS-016, with cumulative weight loss measurements taking place in 500 cycle increments.  FIG. 5  is a line graph depicting the measured cumulative weight loss in grams of the control sample (Control), the first sample (X1), and the second sample (X2) over the course of 4500 cycles on the Taber abrader. As depicted, the test samples (X1 &amp; X2) demonstrated a reduced cumulative weight loss relative to the control sample (Control), particularly above about 2000 cycles, thereby indicating an improvement in abrasion resistance through the addition of zinc oxide as a physical property modifying agent. Further testing revealed that abrasion resistance was most improved with slurries comprising about 14 g/L or more of zinc oxide microparticles (e.g., zinc oxide particles having a size of between about 10 μm and about 100 μm), and slurries comprising about 35 g/L or more of zinc oxide nanoparticles (e.g., particles having a size of between about 10 nm and about 100 nm). Other concentrations and sizes of zinc oxide particles are also contemplated. 
     Samples Y1-Y3 
     In another study of the anodized coating process  200 , three AZ31B magnesium panels were given anodized coatings with micro-sized diamond particles added to the slurry  104  with the intent of enhancing the hardness and abrasion resistance of the three test panels. Holding all other variables in the process the same, three different quantities of diamond particles were added to the slurry  104 , with the intent of measuring the abrasion resistance of each of the three samples after treatment. In particular, the first sample (Y1) was immersed in a slurry comprising 10 g/L of diamond particles, the second sample (Y2) was immersed in a slurry comprising 15 g/L of diamond particles, and the third sample (Y3) was immersed in a slurry comprising 20 g/L of diamond particles. A fourth, control sample (Control), was immersed in a slurry having no diamond particles (and no other physical property modifying agents). In each case, the three test samples and the control sample were left to react in the electrochemical bath for 15 minutes. 
     Upon completion of the coating process the control sample and the test samples were subjected to Taber abrasion analysis as defined by 3LS-016, with cumulative weight loss measurements taking place in 250 cycle increments. Referring to  FIG. 6 , a bar graph depicts the measured cumulative weight loss in milligrams of the control sample (Control) and the three test samples (Y1, Y2 and Y3) over the course of 2000 cycles on the Taber abrader. As depicted, the three test samples (Y1, Y2 &amp; Y3) demonstrated a reduced cumulative weight loss relative to the control sample (Control), particularly above about 1500 cycles. The third sample (Y3), which is depicted in  FIG. 7A , demonstrated the best abrasion resistance, with the least amount of cumulative weight loss. 
     Referring to  FIG. 7B , a close-up view through an electron microscope of an area  400  of  FIG. 7A  is depicted. As shown, even after 2000 cycles on the Taber abrader, physical property modifying agents in the form of diamond crystals  402  deposited within the porous magnesium oxide growth layer can be seen adhered to the surface of the anodized coating  404 . It is believed that the presence of these physical property modifying agents  402  are directly responsible for the improved physical properties of the magnesium containing article  106 . 
     The foregoing description, examples, and data are intended to serve as mere illustrations of disclosed embodiments, and should not be used to unduly limit the scope of the claimed invention. Various embodiments of systems, devices, and methods have been described herein. These embodiments are given only by way of example and are not intended to limit the scope of the claimed inventions. It should be appreciated, moreover, that the various features of the embodiments that have been described may be combined in various ways to produce numerous additional embodiments. Moreover, while various materials, dimensions, shapes, configurations and locations, etc. have been described for use with disclosed embodiments, others besides those disclosed may be utilized without exceeding the scope of the claimed inventions. 
     Persons of ordinary skill in the relevant arts will recognize that the subject matter hereof may comprise fewer features than illustrated in any individual embodiment described above. The embodiments described herein are not meant to be an exhaustive presentation of the ways in which the various features of the subject matter hereof may be combined. Accordingly, the embodiments are not mutually exclusive combinations of features; rather, the various embodiments can comprise a combination of different individual features selected from different individual embodiments, as understood by persons of ordinary skill in the art. Moreover, elements described with respect to one embodiment can be implemented in other embodiments even when not described in such embodiments unless otherwise noted. 
     Although a dependent claim may refer in the claims to a specific combination with one or more other claims, other embodiments can also include a combination of the dependent claim with the subject matter of each other dependent claim or a combination of one or more features with other dependent or independent claims. Such combinations are proposed herein unless it is stated that a specific combination is not intended. 
     Any incorporation by reference of documents above is limited such that no subject matter is incorporated that is contrary to the explicit disclosure herein. Any incorporation by reference of documents above is further limited such that no claims included in the documents are incorporated by reference herein. Any incorporation by reference of documents above is yet further limited such that any definitions provided in the documents are not incorporated by reference herein unless expressly included herein. 
     For purposes of interpreting the claims, it is expressly intended that the provisions of 35 U.S.C. § 112(f) are not to be invoked unless the specific terms “means for” or “step for” are recited in a claim.