P-Ca-V composite phosphating solution on magnesium alloy surface and chemical conversion processing method

Abstract

The invention relates to a composite phosphating solution of P-Ca-V on the surface of a magnesium alloy and a method for chemical conversion treatment. The solution is characterized in that each liter of the composite phosphating solution comprises the following compositions: 4 to 20 milliliters of 85 percent phosphoric acid of, 5 to 30 grams of sodium dihydrogen phosphate, 10 to 40 grams of calcium nitrate, 0.5 to 10 grams of benzene sulfonic acid sodium salt, 0.5 to 5 grams of ammonium metavanadate, and the balance being water. The method comprises the following steps: pre-degreasing, degreasing, secondary water washing, acid washing, secondary water washing, alkaline etching, secondary water washing, chemical transformation, secondary water washing, pure water washing, and drying. Taking an AZ91D magnesium alloy as an example, 48 hours after a corrosion resistance salt spray test after the treatment by the method of the invention, the corrosion area of the AZ91D magnesium alloy is less than 1 percent; the paint film adhesive force is at 0 level by a grid method and is obviously superior to the performance of a chromate conversion coating; and the formed chemical conversion coating does not contain crystal water. The composite phosphating solution has the synergistic reaction of Ca and V, as well as the functions of a corrosion inhibitor and a wetting agent of the benzene sulfonic acid sodium salt.

Description

technical field [0001] The invention provides a metal surface treatment technology, specifically a P-Ca-V composite phosphating solution on the surface of a magnesium alloy and a surface treatment method for its chemical transformation. Background technique [0002] With the rapid growth of demand for magnesium alloys in aerospace, communications, automobiles, electronics and other fields, the research on its corrosion resistance has attracted widespread attention at home and abroad. Chemical oxidation treatment is one of the important ways to prevent corrosion of magnesium alloys. Among them, the chromate chemical oxidation process represented by the DOW1 and DOW7 processes developed by DOW Chemical Company of the United States was the earliest and widely used. However, due to the strong carcinogenicity of chromium, chromate treatment does not meet the requirements of environmental protection. The development of chromium-free chemical oxidation treatment process and treatm...

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Problems solved by technology

However, the existing phosphate-based chemical conversion coatings often have the disadvantage of insufficient corrosion resistance, and their corrosion resistance is usually worse than that of chromate coatings. It is difficult to pass the salt spray test for a long time or a long time, and cannot meet the requirements of 3C magnesium products. (3C refers to computers, electronic communication products and household electronic products) and it is difficult to effectively replace chromate treatment. Its main disadvantage is that the film layer is loose and porous, and often contains crystal water. During the drying process of the film, the surface occurs Due to the syneresis effect, a large number of network cracks are formed, making it difficult to maintain long-term corrosion resistance

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