Study On Zinc Phosphating Technologies And Performance Of Aluminium Alloy

The surface treatment can improve the corrosion resistance of aluminium alloy effectively. The chromate surface treatment is one of the importmant methods to improve the corrosion resistance of aluminium alloy. Because of the toxicity and environmental pollution for chromate surface treatment, the low or non-toxic surface treatment become imperative. The exploitation of chromate-free phosphating technology which has better practicability and environmental friendly is the developing direction. This paper mainly studied the zinc phosphating technology for LY12 aluminum alloy.The optimum techniques of phosphating composition content were obtained by single factor experiment and orthogonal test. The best combination of content components: Zn(H₂PO₄)₂·2H₂O 11g/L, Zn(NO₃)₂·6H₂O 35g/L, NaClO₃ 2g/L, NaF 2.5g/L. The results show that the phosphating film is light grey, bright and uniform and possesses perfect corrosion resistance with the film color changing in the dropping experiment after 60 seconds. The coating consisted of Zn,P,O were investigated by SEM and EDS energy spectroscope analysis. Crystalline substance was found on the surface of aluminum alloy. The stacking mode of the flaky crystal is more orderly, the maximum length of the crystal flakes is 6μm.The optimum techniques of phosphating conditions were obtained by same method. The best combination of the phosphating conditions: phosphating solution volume 100ml, phosphating time 20min, phosphating temperature 50℃, H₃PO₄ 3g/L. The results show that the phosphating film is light grey, bright, uniform and possesses perfect corrosion resistance with the film color changing in the dropping experiment after 60 seconds. The coating consisted of Zn,P,O were characterized by SEM and EDS energy spectroscope analysis. Crystalline substance was found on the surface of aluminum alloy. The stacking mode of the flaky crystal is more chaotic, the maximum length of the crystal flakes is 8μm.The optimum techniques of the zinc phosphating technology were obtained by the best combination of the content components and the phosphating conditions. The best combination of the zinc phosphating technology: Zn(H₂PO₄)₂·2H₂O 11g/L, Zn(NO₃)₂·6H₂O 35g/L, NaClO₃ 2g/L, NaF 2.5g/L, phosphating solution volume 100ml, phosphating time 20min, phosphating temperature 50℃, H₃PO₄ 3g/L. The results show that the phosphating film is light grey, bright, uniform and possesses perfect corrosion resistance with the film color changing in the dropping experiment is 68 seconds. The weight of phosphating film is 5.46g/m² and the linear polarization resistance is 5034?. The coating consisted of Zn,P,O were characterized by SEM and EDS energy spectroscope analysis. Crystalline substance was found on the surface of aluminum alloy.The stacking mode of the flaky crystal is more orderly, the maximum length of the crystal flakes is 8μm.