Dark colored electroceramic coatings for magnesium

Abstract

This invention relates to articles having magnesium-containing metal surfaces with a black, brown or bronze electroceramic coating, chemically bonded directly to the magnesium metal surfaces, the coating having an outer darkly colored layer and an underlying interfacial layer. Articles having a composite coating comprising first sectors of the electroceramic coating and second sectors comprising organic and/or inorganic components different from the electroceramic coating are also provided. The invention further relates to processes of making and using the articles.

What is claimed is: 
     
         1 . A method of depositing a dark colored coating on magnesium or magnesium alloy metal surfaces comprising:
 A) providing an alkaline electrolyte and a cathode in contact with the alkaline electrolyte; the alkaline electrolyte, which may be a solution or dispersion, comprising water, an organic amine, a source of phosphorus, and at least one water-soluble or water-dispersible source of at least one transition metal element;   B) placing an article having at least one metallic magnesium or magnesium alloy surface in contact with the electrolyte and electrically connected thereto such that the surface acts as an anode;   C) passing a current between the anode and cathode through the electrolyte solution for a time effective to generate a first layer of an inorganic-based coating chemically bonded directly to the magnesium or magnesium alloy metal surface, the first layer appearing black, brown, bronze or gray to the unaided human eye;   D) removing the article having the at least one metallic magnesium or magnesium alloy surface coated with the first layer of an inorganic-based coating from the alkaline electrolyte and optionally rinsing and drying the article;   E) optionally post-treating at least the first layer of the inorganic-based coating by
 1) contacting the first layer of the inorganic-based coating with a post-treatment composition different from the inorganic-based coating, the post-treatment composition optionally being reactive with the inorganic-based coating; and/or 
 2) after step 1) if present, applying to the first layer of the inorganic-based coating, a polymeric composition thereby forming a second layer comprising organic polymer chains and/or inorganic polymer chains having a layer thickness of 0.1 micron to 15 microns; and 
   F) optionally applying a layer of paint after the post-treating step.   
     
     
         2 . The method of  claim 1 , wherein said method is performed in the absence of any step prior to step B) that deposits a material containing silicon and/or fluorine on the magnesium surface. 
     
     
         3 . The method of  claim 1 , wherein the organic amine is monoethanolamine and the at least one transition metal element comprises one or more of iron, vanadium and tungsten. 
     
     
         4 . The method of  claim 1 , wherein the alkaline electrolyte contains less than 100 ppm silicon or aluminum and is essentially free of fluorine and of tertiary amines. 
     
     
         5 . The method of  claim 1 , wherein the organic amine is a primary monoamine in the absence of cyclic amines, and the at least one transition metal element consists of iron or vanadium or tungsten. 
     
     
         6 . The method of  claim 3 , wherein the organic amine is monoethanolamine, the source of phosphorus is phosphoric acid, and the at least one transition metal element comprises iron and vanadium and the alkaline electrolyte has a pH of at least 10.2. 
     
     
         7 . The method of  claim 3 , wherein the organic amine is monoethanolamine, the source of phosphorus is phosphoric acid, and the at least one transition metal element comprises tungsten. 
     
     
         8 . The method of  claim 1 , wherein the alkaline electrolyte is vanadium free, the organic amine is monoethanolamine, the source of phosphorus is phosphoric acid, and the at least one transition metal element comprises iron and optionally a second transition metal element other than vanadium. 
     
     
         9 . The method of  claim 1 , wherein the organic amine is a primary monoamine in the absence of cyclic amines, and the at least one water-soluble or dispersible source of at least one transition metal element comprises iron citrate. 
     
     
         10 . The method of  claim 1 , further comprising performing at least one step selected from cleaning, etching, deoxidizing, desmutting, and combinations thereof prior to placing the magnesium containing article in contact with the alkaline electrolyte such that prior to generating the first layer, from 0.05 to 50 g/m 2  of metal is removed from the bare metallic magnesium or magnesium alloy surface. 
     
     
         11 . The method of  claim 1 , further comprising a step of masking a portion of the magnesium containing article prior to placing the at least one metallic magnesium or magnesium alloy metal surface in contact with the alkaline electrolyte. 
     
     
         12 . The method of  claim 1 , comprising controlling temperature and concentration of the alkaline electrolyte and providing a selected waveform of the current in step E) for a time sufficient to thereby produce the inorganic-based coating at a thickness of 1-40 microns and forming the first layer in step E) utilizes less than 10 kWh per square meter of the metal surface coated. 
     
     
         13 . The method of  claim 1 , wherein after step E), no more than 10 mg/m 2  of the inorganic-based coating is removed. 
     
     
         14 . The method of  claim 12 , wherein said current is pulsed direct current having an average voltage in a range of 50 to 700 volts. 
     
     
         15 . An article comprising at least one magnesium or magnesium alloy metal surface coated according to  claim 1 . 
     
     
         16 . An article comprising at least one metallic magnesium or magnesium alloy surface coated with a dark-colored first layer of an inorganic-based coating chemically bonded directly to the at least one metallic magnesium or magnesium alloy surface wherein the inorganic-based coating has a bilayer structure, comprising:
 a. a first sub-layer directly bonded to the metallic magnesium or magnesium alloy surface at a first interface, said first sub-layer comprising Mg, O, C, P and at least one transition metal element;   b. a second sub-layer integrally connected to the first sub-layer at a second interface, said second sub-layer comprising external surfaces at an outer boundary of the inorganic-based coating, and optionally internal surfaces defined by pores in the second sub-layer lying interior to the outer boundary of the inorganic-based coating and in communication therewith, said second sub-layer comprising the Mg, O, C, P and at least one transition metal element;   wherein the weight percent of C in the second sub-layer is greater than that of the first sub-layer.   
     
     
         17 . The article of  claim 16 , where the weight percent of C in the second sub-layer exhibits an increasing concentration gradient from the second interface to the external surfaces of the inorganic-based coating. 
     
     
         18 . An article having at least one metallic magnesium or magnesium alloy surface and deposited thereon a composite coating, said composite coating comprising:
 a. a matrix formed by a first layer of an inorganic-based coating chemically bound directly to the at least one metallic magnesium or magnesium alloy surface, said matrix having pores and internal surfaces defined by the pores, at least some of said pores being in communication with an external surface of the first layer and forming openings therein; and   b. a second component, different from the inorganic-based coating, applied to at least a portion of the matrix comprising the pores, said second component being in contact with at least some of the internal surfaces and external surfaces.   
     
     
         19 . The article of  claim 18 , further comprising a second layer that is different from the inorganic-based coating and is adhered to at least external surfaces of the inorganic-based coating. 
     
     
         20 . The article of  claim 16 , further comprising a second layer that is different from the inorganic-based coating and is adhered to at least external surfaces of the inorganic-based coating. 
     
     
         21 . A plasma electrolytic deposition electrolyte comprising: an aqueous alkaline solution or dispersion, which comprises water, a water-soluble or dispersible organic amine present in an amount of about 50 to about 500 g/l, a source of phosphorus selected from water-soluble oxy acids and salts thereof present in an amount of about 10 to about 85 g/l, and at least one water-soluble or dispersible source of at least one transition metal. 
     
     
         22 . The plasma electrolytic deposition electrolyte of  claim 21 , wherein the aqueous alkaline solution or dispersion contains less than 100 ppm silicon or aluminum and is essentially free of fluorine and tertiary amines. 
     
     
         23 . The plasma electrolytic deposition electrolyte of  claim 21 , wherein the organic amine is a primary monoamine in the absence of cyclic amines, and the at least one transition metal element consists of iron or vanadium or tungsten. 
     
     
         24 . The plasma electrolytic deposition electrolyte of  claim 23 , the at least one water-soluble or dispersible source of at least one transition metal element comprises iron citrate. 
     
     
         25 . The plasma electrolytic deposition electrolyte of  claim 21 , wherein the organic amine is monoethanolamine and the at least one transition metal element comprises one or more of iron, vanadium and tungsten. 
     
     
         26 . The plasma electrolytic deposition electrolyte of  claim 21 , wherein the organic amine is monoethanolamine, the source of phosphorus is phosphoric acid, and the at least one transition metal element comprises iron and vanadium and the alkaline electrolyte has a pH of at least 10.2. 
     
     
         27 . The plasma electrolytic deposition electrolyte of  claim 21 , wherein the organic amine is monoethanolamine, the source of phosphorus is phosphoric acid, and the at least one transition metal element comprises tungsten. 
     
     
         28 . The plasma electrolytic deposition electrolyte of  claim 21 , wherein the electrolyte is vanadium free, the organic amine is monoethanolamine, the source of phosphorus is phosphoric acid, and the at least one transition metal element comprises iron and optionally a second transition metal element other than vanadium. 
     
     
         29 . A storage-stable two pack system comprising:
 a. a Part A containing water; a source of phosphorus; one or more water soluble salts of transition metals, said transition metals comprising iron, vanadium and/or tungsten; wherein Part A has a mass ratio of phosphorus to total amount of transition metal from 4:1 to 1:1; and   b. a Part B containing organic amine;   wherein Part A and Part B are provided in amounts such that the mass ratio of Part A to Part B is in a range from 1:1 to 2:1.