Effect of Different Aging Treatments on the Microstructure and Corrosion Resistance of ADC12 Alloy

The effects of T6 treatment and double aging treatment on the microstructure and corrosion resistance of ADC12 alloy were investigated using optical microscopy, scanning electron microscopy, energy-dispersive spectroscopy, and x-ray diffractometry. The results show that the T6 and DA treatments lead to higher hardness values (120 and 125 HV, respectively) compared to the as-cast ADC12 alloys, with about 23.7 and 28.9% increases, respectively. The DA treatment resulted in the highest UTS, YS, and elongation, with about 32.3, 14.6, and 114.3% higher values, respectively, compared to the as-cast alloys. Both immersion and electrochemical tests have demonstrated that ADC12 alloys have improved corrosion resistance after T6 treatment and double aging treatment. Due to Si phase, which is the cathode phase, being refined significantly, the microstructure of "large anode–small cathode" is formed. However, DA treatment shows a more significant improvement in corrosion resistance, as the weight loss corrosion rate and corrosion current density of ADC12 + DA are 71.53 and 83.71% lower than those of ADC12 + T6, respectively. Compared to the T6 treatment, the double aging transforms the grain boundary precipitation phase into a discontinuous distribution, cutting off the anode continuous corrosion channel and thus improving the corrosion resistance of ADC12 alloy.