Effect of Pre-strain on Microstructure and Corrosion Behavior of a Novel High-Zn Containing Al-Zn-Mg-Cu Alloy

The effect of pre-strain on microstructure, mechanical property and corrosion behavior of a novel high-Zn containing Al-Zn-Mg-Cu alloy was investigated by the means of x-ray diffraction, electron back-scattered diffraction, optical profilometer, laser scanning microscope, scanning electron microscope and transmission electron microscopes. The results show that the introduction of pre-strain leads to a decrease in the ultimate strength and elongation of the alloy, which resulting from low density and the larger average size of matrix precipitates. In addition, the ability to resist pitting corrosion, intergranular corrosion and exfoliation corrosion was significantly improved by pre-strain owing to the discontinuous grain boundary precipitates, wider precipitation-free zone and residual dislocations. Among all the pre-strained samples, the 2% pre-strained sample exhibits the best comprehensive performance with optimal corrosion resistance and minimal strength loss; further increasing the degree of pre-stretching, the high-density dislocation and coarsened precipitates within matrix and at grain boundaries accelerated the enrichment of hydrogen at the tip of corrosion crack, resulting in lower corrosion resistance compared with the samples with 2% pre-strain.