Aluminum-zinc phosphate coating and use method thereof

Abstract

The invention discloses an aluminum-zinc phosphate coating and a use method thereof. The coating is prepared from the following components in parts by weight: 10 to 50 parts of Al(H2PO4)3, 1 to 20 parts of Zn(H2PO4)3, 1 to 10 parts of TEOS, 60 to 90 parts of H2O and 10 to 70 parts of Al2O3 powder. The modified aluminum-zinc phosphate coating is prepared on the surface of a cast aluminum alloy through a steam-assisted heat treatment method. According to the invention, Al(H2PO4)3 and Zn(H2PO4)3 are used as composite binders, so the reaction activity of the coating and a cast aluminum matrix is improved; as the TEOS is added as a modifier, the compatibility of nano-SiO2 and the composite binders can be improved, and the crosslinking density of the coating is improved; and the prepared modified aluminum zinc phosphate coating is uniform and flat, is tightly combined with the matrix, mainly comprises Zn3(PO4)2, AlPO4, AlPO4. 2H2O and SiO2, and can remarkably improve the corrosion resistance of an aluminum alloy casting.

Description

technical field [0001] The invention belongs to cast aluminum alloy surface treatment paint and its application method, in particular to an aluminum-zinc phosphate paint and its preparation method. Background technique [0002] Aluminum alloy is the most widely used non-ferrous metal material in industrial production. Because of its high specific strength, high specific stiffness, excellent electrical and thermal conductivity, and good machinability, it is widely used in automotive, aerospace, shipbuilding and other industrial fields. widely used. [0003] The chemical properties of aluminum and aluminum alloys are active, and their standard electrode potential is -1.66V (at 25°C). When aluminum comes into contact with a more reactive metal to form a galvanic cell, the aluminum acts as the anode and corrodes. In the atmospheric environment, the surface of aluminum and aluminum alloys will be oxidized to produce an oxide film (mainly Al 2 o 3 ), can provide a certain prot...

AI Technical Summary

Problems solved by technology

In the atmospheric environment, the surface of aluminum and aluminum alloys will be oxidized to produce an oxide film (mainly Al 2 o 3 ), can provide a certain protective effect, but the thickness of this naturally formed oxide film is small, generally not exceeding 10nm, and the surface of the film is loose and porous, easy to break, and has poor corrosion resistance. Erosion of corrosive media gradually fails

At the same time, with the aggravation of environmental problems such as acid rain, sulfur and nitrides such as salt, sulfur dioxide, and nitrogen dioxide in the atmosphere will settle and enrich on the surface of castings, forming an electrolyte solution in a humid environment, and aluminum alloys are more prone to pitting corrosion. Cause irreversible casting damage or even failure

[0004] Aluminum alloy castings are irregular in shape and have complex second phases. In the prior art, a continuous phosphate coating can be prepared on the surface of aluminum alloy castings by steam-assisted heat treatment. However, since the surface of aluminum alloy is coated with aluminum and Magnesium phosphate coating, resulting in the formation of phosphate coating is a multi-layer composite structure, so each coating is prone to defects such as microcracks and pores, which become channels for corrosion medium erosion, reducing the durability of the overall coating performance

Moreover, due to the need to prepare coatings separately in the aluminum-magnesium phosphate composite coating process, the complexity of the preparation process is increased.

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