Optimizing Homogenization Heat Treatment of Al-Zn-Mg-Cu-Zr-0.15Er Alloy

The effects of the homogenization conditions on the microstructure of Al-Zn-Mg-Cu-Zr-0.5Er alloy were investigated by differential scanning calorimetry (DSC), optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), and X-ray diffraction (XRD). The results showed that a lot of coarse phases existed in as-cast Al-Zn-Mg-Cu-Zr-0.5Er alloy. The dissolvable phases at grain boundary consisted of Mg32 (Al, Zn)49. The residual phases dissolved into the matrix gradually during homogenization with increasing temperature and prolonging holding time. When the temperature increased to 465°C, and time prolongs to 24h, the main phase disappeared except the Fe and Er enriched phase, as a result of its high melting temperature. Taking into account the precipitation of Al3Er, we used a two-step homogenization .Hence, the optimum parameters of homogenization were 400 °C for 4 h and 465 °C for 24 h, which are good for the presence of coherent, elastically hard and nanosized Al3(Er, Zr) particles and the dissolvable coarse phases .