Effect of Cooling Methods on Microstructure and Corrosion Resistance of Zn-11Al-3Mg-0.2Si-xTi Alloy

Zn-11Al-3Mg-0.2Si-xTi (x=0wt%, 0.09wt%) alloys were prepared by steel die cooling, copper die cooling and copper die+water cooling, and the effects of cooling method on the microstructure and corrosion resistance of Zn-11Al-3Mg- 0.2Si-xTi alloys were studied by means of scanning electron microscope (SEM), energy dispersive spectrometer (EDS), neutral salt spray test and electrochemical test. The results show that alloying method and controlled cooling rate have important influence on the microstructure and properties of Zn-11Al-3Mg-0.2Si alloy. The Zn-11Al-3Mg-0.2Si alloy is composed of α-Al, η-Zn, eutectic MgZn₂, Zn/Al/MgZn₂(Mg₂Zn₁₁) ternary eutectic. The addition of Ti and the increase of cooling rate can effectively inhibit the growth of Mg₂Zn₁₁ phase. Under the copper die+water cooling condition, the α-Al dendrites in Zn-11Al-3Mg-0.2Si-0.09Ti alloy are refined, the nucleation amount increases, the eutectic MgZn₂ phase size decreases, the divorced eutectic structure in the alloy is improved, the content of Zn/Al/MgZn₂ ternary eutectic increases, and the Mg₂Zn₁₁ phase disappears, and the alloy shows the best corrosion resistance properties.