Preparation method of composite film layer on surface of rare earth magnesium alloy structural part

Abstract

The invention discloses a preparation method of a composite film layer on the surface of a rare earth magnesium alloy structural part. The preparation method sequentially comprises the steps of oil removal, primary water washing, micro-arc oxidation, secondary water washing, electrophoresis, tertiary water washing and drying and curing. A micro-arc oxidation electrolyte is an aqueous solution containing sodium silicate, sodium fluoride, sodium hydroxide, graphene, Cu(NO3)2 and triethanolamine, electrical parameters of micro-arc oxidation are as follows: the positive current density is 5-15A / dm<2>, the negative current density is 2-3A / dm<2>, the positive duty ratio is 25-70%, the negative duty ratio is 40-50%, the positive frequency is 200-800Hz, the negative frequency is 300-500Hz, the positive and negative stages are both one stage, the micro-arc oxidation time is 10-20 min, electrophoresis liquid for electrophoresis is an aqueous solution containing acrylate, a delustering agent andcarbon black pigment, and electrical parameters of electrophoresis are as follows: the voltage is 50-80V, and the time is 10-30s; and through the coordination effect of micro-arc oxidation and electrophoresis, the composite film layer meeting the requirements of high hardness, high bonding strength and ultraviolet aging resistance at the same time can be prepared.

Description

technical field [0001] The invention relates to the technical field of metal surface treatment, in particular to a method for preparing a composite film layer on the surface of a rare earth magnesium alloy structural part. Background technique [0002] As a "green engineering material in the 21st century", magnesium alloy has high specific strength, specific stiffness, excellent electrical and thermal conductivity and machinability. In recent years, in order to meet the requirements of lightweight development of automobiles, national defense science and industry, and 3C products, it is imminent to solve the problem of magnesium alloy protection. [0003] The oxide film P-B ratio (pilling-bedworth ratio: the ratio of the volume of each metal ion in the oxide film formed by the combination of metal and oxygen on the metal surface to the volume of each metal atom in the metal) formed by magnesium alloy in the natural environment is less than 1 , in a complex environment, the c...

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Problems solved by technology

[0004] In the Chinese patent with the application number 201610459473.7 and the Chinese patent with the application number 201610804669.5, the magnesium alloy is subjected to micro-arc oxidation and sol-gel sealing treatment to obtain a film layer with low porosity and salt spray corrosion resistance, but the The hardness of the coating produced by the process is still low, and the sealing process is difficult to prepare a uniform coating on large-sized workpieces

Application number is 201010500023.0 Chinese patent and application number is 201110406762.8 in the Chinese patent, respectively utilize micro-arc oxidation-organic silicon paint spraying, micro-arc oxidation-electrophoresis-spraying acrylic primer-spraying organosilicon ceramics process to prepare composite topcoat, but Using this process, the steps are cumbersome and complicated, and there is no performance evaluation for the superimposed atmospheric exposure conditions, especially for workpieces with complex structures, the small holes are prone to be blocked when the topcoat is applied

In the Chinese patent application number 201310536595.8, a method for preparing a magnesium alloy surface micro-arc oxidation-electrophoretic composite coating is disclosed, which solves the problems of poor bioactivity of the existing magnesium alloy itself and poor bonding force of the composite film layer. However, in this In the technology, after the prepared oxide film is sealed by electrophoresis, the scanning results show that the surrounding of the hole is uneven, the quality of the film is poor, and the bonding force is difficult to meet the requirements of engineering applications.

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