Method for surface treatment of magnesium or magnesium alloy by anodization

Abstract

Disclosed herein is a method for the surface treatment of magnesium or a magnesium alloy by anodization to form an anodized oxide coating on the magnesium or magnesium alloy. The method comprises: removing impurities and an oxide layer present on the surface of magnesium or a magnesium alloy using a strongly alkaline aqueous solution (pretreatment); and immersing the pretreated magnesium or magnesium alloy in an alkaline electrolyte and applying a direct current having a current density of 3 A/dm 2 or less to the electrolyte to form a magnesium oxide coating (microarc plasma anodization).

1 . A method for the surface treatment of magnesium or a magnesium alloy by anodization to form an oxide coating on the magnesium or magnesium alloy, the method comprising:
 removing impurities and an oxide layer present on the surface of magnesium or a magnesium alloy using a strongly alkaline aqueous solution and thereby forming a pretreated magnesium or magnesium alloy; and   immersing the pretreated magnesium or magnesium alloy in an alkaline electrolyte and applying a direct current having a current density of 3 A/dm 2  or less to the electrolyte to form a magnesium oxide coating through microarc plasma anodization.   
     
     
         2 . The method of  claim 1 , further comprising, after the microarc plasma anodization, washing the magnesium or magnesium alloy, on which the coating is formed, with distilled water, followed by drying with hot air. 
     
     
         3 . The method of  claim 1 , wherein the strongly alkaline aqueous solution used in the pretreatment step comprises 30-60 g/L of KOH, 150-200 g/L of NaOH, 20-30 g/L of an amine oxide, 5-10 g/L of an α-alkoxyisobutyric acid alkyl ester and a wetting agent. 
     
     
         4 . The method of  claim 1 , wherein the alkaline electrolyte used in the immersing step comprises sodium carbonate (Na 2 CO 3 ). 
     
     
         5 . The method of  claim 1 , wherein the alkaline electrolyte used in the immersing step comprises 20-150 g/L of potassium hydroxide (KOH), 20-150 g/L of sodium carbonate (Na 2 CO 3 ), 5-40 g/L of trisodium citrate, 3-40 g/L of potassium fluoride (KF), and 3-40 g/L of ammonium bifluoride (NH 4 HF 2 ).