Intergranular corrosion resistance of Zn modified 5××× series Al alloy during retrogression and re-aging treatment

The effects of retrogression and re-aging treatment on the intergranular corrosion behavior of Al-5.0Mg-3.0Zn alloys are systematically studied. The alloy's strength increases when retrogression temperature increases from 390 °C to 420 °C. Samples retrogressed at 390 °C then re-aged are very susceptible to intergranular corrosion and those retrogressed at 405 °C and 420 °C express good corrosion resistance. Then the alloy's corrosion susceptibility rises with increasing retrogression temperature. Grain boundary precipitates are coarsened and distributed discontinuously with decreasing retrogression temperature. Higher retrogression temperature results in higher Mg and Zn content difference and intergranular corrosion susceptibility.