Paint for preparing aluminum phosphate coating on surface of aluminum alloy and use method of paint

The invention provides paint for preparing an aluminum phosphate coating on the surface of an aluminum alloy and a use method of the paint. The paint comprises the following raw materials, by weight, 10-70 parts of Al(H2PO4)3, 30-80 parts of pure water, 1.1-1.3 times of the total chemical reaction required amount of pure water and Al(H2PO4)3 of Al2O3 powder. The use method of the paint comprises the following steps: 1) the raw materials are weighed proportionally, and are mixed uniformly and the paint is obtained; 2) an aluminum alloy sample is placed in an alkaline solution for alkaline washing, and then is washed with the pure water, finally the aluminum alloy sample is subjected to natural drying for use; and 3) the surface of the dried aluminum alloy is coated with the paint, then the aluminum alloy is placed in a water vapor environment, and an aluminum alloy casting provided with the aluminum phosphate coating is obtained. The aluminum phosphate coating can be formed on the surface of the aluminum alloy, the corrosion resistance of the aluminum alloy can be improved, the technical treatment temperature is lower than the aging heat treatment temperature usually used for the aluminum alloy, and the use method can act as a final treatment technology to be applied to product production.