Effect of ageing on precipitation evolution and corrosion behaviour of Al–Zn–Mg–Cu alloy

Abstract

The Al–Zn–Mg–Cu alloy was subjected to 4 passes equal channel angular pressing (ECAP) at 400°C, followed by different solutions and ageing treatments. The size, type and distribution of precipitates in aluminium matrix are different in different ageing treatments. In single-stage ageing, a large number of η′ precipitates and Guinier-Preston-II (GP-II) zones are generated in the aluminium matrix. The precipitates are mainly MgZn2 (η) precipitates and η′ precipitates during the double-stage ageing. The size and type of precipitates in three-stage ageing are similar to those in two-stage ageing. Simultaneously, the single-stage ageing sample has poor corrosion resistance and good hardness. Two-stage ageing and three-stage ageing samples have better corrosion resistance, but their hardness is lower than that of single-stage ageing.