Passivation solution used for trivalent chromium passivation of high-silicon die-casting aluminum alloy and passivation method

Abstract

The invention belongs to the technical field of metal surface treatment, and particularly relates to a passivation solution used for trivalent chromium passivation of a high-silicon die-casting aluminum alloy. The passivation solution used for trivalent chromium passivation of the high-silicon die-casting aluminum alloy comprises chromic nitrate with a mass concentration of 3-10 g / L, an organic acid complexing agent with a mass concentration of 2-8 g / L, a polyhydroxy alcohol complexing agent with a mass concentration of 1-6 g / L, a corrosion resistant agent with a mass concentration of 1-3 g / L and a film-forming accelerant with a mass concentration of 1-3 g / L. A passivation technology of the passivation solution used for trivalent chromium passivation of the high-silicon die-casting aluminum alloy comprises the steps of oil removal and degreasing, hot water washing, activation, water washing, passivation, water washing, hot water washing and drying. According to the scheme, the corrosion resistant agent is added to improve the corrosion resistant performance of a passive film, and the corrosion resistant performance of the high-silicon die-casting aluminum alloy is improved; after the die-casting aluminum alloy is passivated by the passivation solution, a thin film which is slightly light blue is formed, and the appearance color of a die-casting aluminum alloy part is not changed; and an anti-corrosion effect of an automobile light-weight part can be guaranteed.

Description

technical field [0001] The invention belongs to the technical field of metal surface treatment, and in particular relates to a passivation solution and a passivation method for passivation of trivalent chromium in high-silicon die-casting aluminum alloys. Background technique [0002] The cast aluminum alloy used in automobiles is easily corroded without surface treatment. White corrosion spots will appear 2 to 4 hours after exposure to water, so anti-corrosion treatment is required. Previously, hexavalent chromium passivation can better meet the corrosion resistance requirements of aluminum alloys. However, the European Union and the United States have imposed strict restrictions on chemical substances used in automobiles. Whether it is the Rohs directive of the European Union or the laws of the United States, strict restrictions have been imposed on the content of harmful substances in complete vehicles and parts, and hexavalent The application of chromium in the surface ...

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Problems solved by technology

As the amount of silicon increases, the amount of wear, corrosion, coefficient of linear expansion, density, and electrical conductivity all drop linearly. Although the above scheme has a certain effect, the corrosion resistance of high-silicon die-casting aluminum, especially aluminum alloys with a silicon content of more than 10%. Under the condition of higher requirements, the corrosion resistance performance cannot be satisfied

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