Method for treating surface of magnesium or magnesium alloy

Abstract

A method for surface treatment is disclosed. The method is achieved by forming a MgO film on a metal surface through anode processing of Mg or Mg alloy in an alkaline solution. The alkaline solution includes a hydroxide, a thickening agent, and a film adjusting agent. As the method is performed, the target object is immersed in the alkaline solution, and the target object is connected to an anode with an average electric current density of 1˜5 A/dm, at a temperature of 0˜30° C., and within a time period of 10˜120 minutes to form a film of 5˜25 μm. The forming rate of the film of the method of the present invention is fast, and the formed film is of little stress.

1 . A surface treatment method, which comprises: 
 (A) providing a metal of Mg or Mg Alloy, a surface treatment composition, and a tank, wherein said surface treatment composition comprises a hydroxide, a film thickening agent, and a film adjustment agent, wherein said tank is provided with an electrode and said surface treatment composition therein;    (B) immersing said Mg or Mg Alloy or a surface thereof into said surface treatment composition in said tank;    (C) flowing an electric current through said Mg or Mg Alloy and said electrode in said tank; and    (D) terminating the electric current, and removing the treated Mg or Mg Alloy from said tank.    
   
   
       2 . The method as claimed in  claim 1 , wherein the Mg or Mg Alloy during said Step (C) for is at 0˜40° C.  
   
   
       3 . The method as claimed in  claim 1 , wherein said surface treatment composition in Step (B) has a pH value greater than 9.  
   
   
       4 . The method as claimed in  claim 1 , wherein said film thickening agent in Step (A) is selected from the group consisting of aluminate, silicate, vanadate, molybdates, tungstates, and a combination thereof.  
   
   
       5 . The method as claimed in  claim 1 , wherein said film adjustment agent in Step (A) is selected from the group consisting of potasium dihydrogen phosphate, sodium dihydrogen phosphate, tripotassium phosphate, trisodium phosphate, oxalic acid, succinic acid, fatty acid, malic acid, and a combination thereof.  
   
   
       6 . The method as claimed in  claim 1 , wherein said hydroxide in Step (A) is selected from the group consisting of sodium hydroxide, potassium hydroxide, and a combination thereof.  
   
   
       7 . The method as claimed in  claim 1 , wherein said surface treatment composition in Step (A) has a concentration of said hydroxide of 10˜100 g/L.  
   
   
       8 . The method as claimed in  claim 1 , wherein said Mg and Mg alloy in Step (A) is a Mg-riched alloy or casting Mg alloy.  
   
   
       9 . The method as claimed in  claim 1 , wherein said surface treatment composition in Step (A) has a concentration of said film thickening agent of 10˜150 g/L.  
   
   
       10 . The method as claimed in  claim 1 , wherein said surface treatment composition s in Step (A) has a concentration of aid film adjustment agent of 10˜300 g/L.  
   
   
       11 . The method as claimed in  claim 1 , wherein said electric current in said Step (C) is flowed at an average electric current density of 1˜10 A/dm 2 .  
   
   
       12 . The method as claimed in  claim 1 , wherein said Step (C) is carried out in said surface treatment composition for 5˜240 minutes.  
   
   
       13 . The method as claimed in  claim 1 , wherein the Mg-containing material is connected to a positive electrode of a rectifier in Step (C).  
   
   
       14 . The method as claimed in  claim 13 , wherein said rectifier is selected from the group consisting of a d.c. rectifier and a pulse rectifier.  
   
   
       15 . The method as claimed in  claim 14 , wherein said d.c. rectifier is selected from the group consisting of a constant current type d.c. rectifier, a constant voltage type d.c. rectifier, and a constant current density recycle type d.c. rectifier.