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.

Description

FIELD OF THE INVENTION [0001] The present invention relates to a surface treatment method, particularly a surface treatment method applicable on Mg or Mg Alloy. BACKGROUND OF THE INVENTION [0002] Mg alloys are high in strength and light in weight and are widely used on airplanes, vehicles, and electronic products. Since magnesium is capable of forming alloys of high strength with many types of metal, Mg alloys have a wide variety of applications. However, Mg alloys are generally not suitable for mass production due to their disadvantages, such as poor corrosion resistance, and poor wear resistance, etc. Furthermore, due to an ever increasing expansion on the applications of Mg alloys, the demand on the acid-corrosion-resistance of the alloys is also increasing day by day. [0003] In the past, a Mg alloy is usually protected against acid corrosion by coating a protective paint or forming a protective film on the surface of the alloy. In recent years, due to the improvement in technolo...

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Benefits of technology

[0011] The film thickening agent used in the present invention can be any conventional film thickening agent, preferably aluminate, silicate, vanadate, molybdate, tungstate, or a combination thereof, with an arbitrarily applicable concentration in the surface treatment composition. In a preferred embodiment of the present invention, the concentration of the film thickening agent is 10˜150 g / L. The main objective of using the film thickening agent is for growing a film. The film forming rate increases along with an increase in the concentration of the film thickening agent. Under suitable conditions, the objective of the film thickening can be achieved without the need of using high temperature and ultra-high voltage.

[0016] In the present invention the Mg or Mg alloy is capable of forming a film mainly constituted of magnesium oxide ceramic ingredient in an alkaline solution by anodic oxidation treatment, and the magnesium oxide ceramic ingredient is slightly soluble in an alkaline solution by chemical dissolution. Since the surface treatment composition according to the present invention contains no fluoride, such a surface treatment composition will not cause severe environmental pollution. Furthermore, the present invention uses a film thickening agent and a film adjustment agent to achieve an increase in the film forming rate, a reduction in film dissolution rate, a uniform and fine film, a stable dimensional precision of the workpiece, and a reduction on the internal stress of the film.

Problems solved by technology

However, Mg alloys are generally not suitable for mass production due to their disadvantages, such as poor corrosion resistance, and poor wear resistance, etc.

However, a surface formed through such a technique is rough due to the formation of a large amount of penetration sparks, and requires an additional coating treatment.

Furthermore, due to the use of fluoride as a main chemical agent, wastewater from such a treatment is difficult to be treated and has a greater pollution impact on the environment.

However, since a Mg alloy dissolves rapidly in an acidic state, the surface of the resulting film is liable to become rough.

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