INFLUENCE OF THERMAL-RATE TREATMENT ON THE CORROSION RESISTANCE OF MG-7AL-0.4ZN-0.2MN ALLOY

摘要

The influence of thermal-rate treatment on the corrosion resistance of Mg-7Al-0.4Zn-0.2Mn(AZ70) alloy was studied by observing corrosion morphology, measuring corrosion potential and salt-spray corrosion rate. The results show that the corrosion behavior of AZ70 alloy depends on both its microstructure and iron content. When the superheat-temperature(Ts) is 810°C, the corrosion resistance of AZ70 alloy isn't improved obviously. When Ts=850°C, finer grains are achieved, the size of β phase and the distance between β phase is small, so that the corrosion barrier effect of β phase on α phase are better. On the other hand, the iron content isn't increased much so that the corrosion resistance is improved. The corrosion resistance of AZ70 alloy falls off. When Ts=890°C. At a same superheat-temperatures, the corrosion resistance is improved with the increase of chilling rate. On comprehensive consideration of microstructure and corrosion resistance of AZ70 alloy, the optimal TRT technology is that Ts=850°C and Vc °C=2.0 /s. Meanwhile, the corrosion resistance is the best. The corrosion potential is 15mV higher than that of un-TRT treated alloy and the salt-spray corrosion rate is 21.9% lower than that of un-TRT treated alloy.