Magnesium alloy surface phosphorus-free chromium-free conversion coating and application method thereof

Abstract

The invention discloses a preparation method of a magnesium alloy surface phosphorus-free chromium-free conversion coating, which comprises the following steps: removing oil from the magnesium alloy, cleaning with acid, activating and treating the magnesium alloy in a conversion solution, which is composed of metavanadate, villiaumite, rare-earth salt and alkaline earth metal salt, at 10-99 DEG C under the pH value of 0.5-4.0 for 1-45 minutes, thereby forming a phosphorus-free chromium-free conversion coating on the magnesium alloy surface. The phosphorus-free chromium-free conversion coating has the advantages of excellent corrosion resistance and uniform color, and has certain self-recovery capacity.

Description

Technical field [0001] The invention belongs to the technical field of metal surface treatment, and relates to magnesium alloy surface treatment, in particular to a phosphorous and chromium-free conversion film solution on the magnesium alloy surface and a use method thereof. Background technique [0002] As a commonly used light metal material, magnesium alloy has the advantages of low density, specific strength, high specific stiffness, low elastic modulus, good casting and electromagnetic shielding performance, and easy recycling. Magnesium has extremely rich reserves on the earth, and it is being used more and more widely in daily life and industrial fields. For example, magnesium alloys are used in automobiles, electronic communications and aerospace fields, with "green materials" and "mechanical structures" "Lightweight star" reputation. However, compared with steel and aluminum, magnesium alloys have active chemical properties, low chemical stability and poor corrosion re...

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Problems solved by technology

However, the stannate treatment method has the disadvantages of polluting the environment and general corrosion resistance; the phosphate treatment method has the disadvantages of eutrophication of the water body and poor corrosion resistance. Eutrophication pollution prevention and control technology and the national environmental protection “Twelfth Five-Year Plan” key areas to implement total phosphorus emission control requirements limit the future application of phosphating technology; Stable, organic compound conversion treatment method cannot be applied to industrial production due to the disadvantage of poor corrosion resistance

[0005] Chinese patents 200810126263.1 and 200810201854.0 respectively disclose a method for phosphating the surface of magnesium alloys. The treatment process of patent 200810126263.1 includes: activation (35°C~55°C)→adjustment (55°C~85°C)→chemical conversion ( 35°C~55°C); patent 200810201854.0 treatment process includes: pre-degreasing, degreasing (55°C~65°C) → pickling (45°C ~ 55°C) → alkali etching (80°C ~ 90°C) → chemical conversion (18°C ~60°C)→drying (120°C), it can be seen that in addition to the shortcomings of high energy consumption and complicated treatment process in the above two patented treatment processes, both patented conversion liquids contain a large amount of phosphate in the waste liquid Difficult to dispose, easy to cause eutrophication of water body

Because the organic compounds in the conversion solution participate in the film-forming reaction, and the corrosion resistance of the organic conversion film is average, the neutral salt spray test only reaches the current industrial application standard of 8 hours, and the organic film still has problems such as aging

In addition, this process uses a high temperature of 100°C to dry the organic film, which also has the disadvantage of wasting a lot of energy

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