Response of mechanical properties and corrosion behavior of Al–Zn–Mg alloy treated by aging and annealing: A comparative study

Abstract

The high strength Al–Zn–Mg plates were processed by combing the hot extrusion and cold rolling. Then, both the artificial aging and annealing were conducted to make a comparative study on the microstructure, mechanical properties, and corrosion resistance. The aged samples were composed of near-equiaxed grains attributed from the static recrystallization during solution process, and owned the main textures of Cube, Goss, Copper, S, and Brass. The precipitate followed the sequence of SSS → GP zone → η′ phase → η phase. With the increase of aging time, the grain boundary precipitations (GBPs) became coarse and discontinuous, and the width of precipitate free zones (PFZs) also increased. In annealed samples, the coarse and elongated grains were finally formed, and the volume fraction of recrystallization textures increased with the extension of annealing time. Moreover, the density of dislocations and the number of MgZn2 phase were both reduced during annealing. The tensile strength along 0° with rolling direction was always the highest in all aged and annealed samples, and the elongation achieved the highest values along 45°. Long-time aging slightly improved the planar anisotropy, while long-time annealing greatly improved the planar anisotropy. The peak aged sample showed a ductility loss of 21.96% during the slow strain rate test in 3.5 wt% NaCl, and a maximum depth of 214.59 μm in intergranular corrosion test. Compared to the annealed sample, the aged one exhibited the worse corrosion resistance due to the wide PFZs and continuously distributed GBPs.