Microstructure, mechanical properties and thermal stability of friction-stir-processed Al-Cu-Mg-Ag alloy

The mechanical properties and thermal stability of Al-Cu-Mg-Ag alloy prepared by friction stir processing and subsequent aging were investigated by scanning electron microscopy, transmission electron microscopy and X-ray diffraction. After peak aging treatment, the mechanical properties in the stir zone are significantly higher than those of the base metal while plasticity stays the same. With increasing rotational speed, the mechanical properties of the stir zone improve and have a stronger age-hardening response, which is mainly attributed to the fine equiaxed grains and the high number density of plate-like omega plates. After the heat exposure, the mechanical properties of the stir zone decreased more drastically compared to the base material. This is because the high density of dislocations and grain boundaries promotes elemental diffusion and accelerates the coarsening of the precipitates in the stir zone.