Effect of Quenching Rate on Microstructure, Mechanical and Corrosion Properties of Al-Zn-Mg-Cu-Cr-Zr Alloy

The quench sensitivity of the corrosion and mechanical properties of an Al-Zn-Mg-Cu-Cr-Zr alloy was investigated utilizing tensile testing, intergranular corrosion experiments and microstructure characterization. The research results indicated that, with a decrease in quenching rate, quenching precipitates sequentially nucleated non-uniformly at grain boundaries (GBs) (η phase), E phase (η phase) and Al3Zr particles (η and T phases). As the quenching rate decreased, the size and area fraction of quenching precipitates increased within the grains, consuming many solute atoms. This led to a reduction in the precipitation of the η′ strengthening phase during the aging process, resulting in a decrease in mechanical properties. Simultaneously, the decrease in quenching rate resulted in a significant increase in the size of the η phase at the GBs, Zn and Mg content, and the width of the precipitate-free zone at the GBs, making the GBs more susceptible to corrosion. This accelerated the rate of corrosion crack propagation along the GBs, reducing the corrosion resistance of the alloy.