Method of making oxide film by anodizing magnesium material

Abstract

An oxide film is formed on an object made of a magnesium material. For the film formation, the object is immersed into an electrolyte that contains insoluble particles and alkali metal hydroxide. In the electrolyte, the object is anodized to be coated with an oxide film. In the presence of the insoluble particles dispersed in the electrolyte, the oxide film takes in nearby particles as it is growing on the object during the anodizing process.

1 . A method of making an oxide film, the method comprising: 
 immersing an object into an electrolyte, the object being made of magnesium or a magnesium alloy; and    forming an oxide film on the object in the electrolyte by anodizing;    wherein the electrolyte comprises insoluble particles and alkali metal hydroxide, the oxide film taking in the insoluble particles as growing on the object.    
     
     
         2 . The method according to  claim 1 , wherein the insoluble particles are made of at least one of alumina, aluminum hydroxide, silica, titanium oxide, and ceramic oxide.  
     
     
         3 . The method according to  claim 1 , wherein the insoluble particles have an average diameter in a range of 5 nm˜10 μm.  
     
     
         4 . The method according to  claim 1 , wherein the insoluble particles have an average diameter in a range of 5 nm˜500 nm.  
     
     
         5 . The method according to  claim 1 , wherein the anodizing is performed by application of an alternating current having a current density in a range of 2A/dm 2 ˜5A/dm 2 .  
     
     
         6 . The method according to  claim 1 , wherein the alternating current has a frequency in a range of 40 Hz˜80 Hz.  
     
     
         7 . The method according to  claim 1 , wherein the electrolyte for performing the anodizing is kept at a temperature in a range of 15° C.˜60° C.  
     
     
         8 . The method according to  claim 1 , wherein the alkali metal hydroxide in the electrolyte has a concentration in a range of 25 g/dm 3 ˜75 g/dm 3 .  
     
     
         9 . The method according to  claim 1 , wherein the electrolyte comprises an aqueous solution of a soluble silicate or oxyacid salt.  
     
     
         10 . The method according to  claim 9 , wherein the soluble silicate in the electrolyte has a concentration in a range of 100 g/dm 3 ˜250 g/dm 3 .  
     
     
         11 . The method according to  claim 9 , wherein the oxyacid salt in the electrolyte has a concentration in a range of 75 g/dm 3 ˜150 g/dm 3 .  
     
     
         12 . The method according to  claim 1 , further comprising a step of forming a coating layer on the oxide film, the coating layer being made of at least one of an organic material, an inorganic material, and a metal oxide sol.  
     
     
         13 . A housing comprising: 
 a housing body made of a magnesium material; and    an oxide film formed on the body;    wherein the oxide film contains particles made of at least one of alumina, aluminum hydroxide, silica, titanium oxide, and ceramic oxide, the particles being taken into the oxide film when the film is caused to grow on the body by anodizing.