Effect of quenching rate and quenching residual stress on precipitation behavior and corrosion properties of a highly-alloyed Al–Zn–Mg–Cu–Zr alloy
Mengjun Long, Feng Jiang, Yuanming Su, Jianan Yang
Abstract
In this work, the effect of quenching rate and quenching-induced residual stress on precipitation behaviors and corrosion properties of a highly-alloyed Al–Zn–Mg–Cu–Zr alloy were systematically investigated through immersion end-quenching test, quenching-induced residual stress and microstructure characterizations, hardness distribution examinations, intergranular and exfoliation corrosion tests, electrochemical analysis and surface Volta potential measurements. The results show that a high quenching rate introduces a considerable generation of surface residual compressive stress on the plate, which decreases rapidly with the quenching rate decreases. At a high quenching rate, the induced residual stress and dislocations promote the heterogeneous nucleation and accelerate the formation of coarsening matrix precipitates (MPts) during artificial aging, leading to a decrease in hardness and corrosion resistance. While at low quenching rates, the overall surface potential fluctuations increase significantly due to the substantial quenching-induced precipitates and the coarsened grain boundary precipitates (GBPs), which induce more electrochemical reactions in a corrosive environment. Furthermore, the wider precipitation free zones (PFZs) serve as continuous high-active anode microchannels for ion exchange, promoting the corrosion development along GBs and toward interior, leading to a considerable reduction in corrosion resistance.