Effect of heating processes during homogenization on the microstructure evolution of Al-Zn-Mg-Cu alloy
Shuaishuai Qin, Xiaojiu Hu, Baokun Lu, Ângelo De Min, Ce Zhou, Bo Wu, Weidong Huang, Xu Huang
Abstract
The effects of homogenization heating methods on microstructural evolution were thoroughly investigated in an Al-Zn-Mg-Cu alloy containing Cr, Mn and Zr. The results revealed that slow heating (SH), rapid heating (RH) and two-step heating (SH300) can affect both the types and contents of residual phases after 465 °C/20 h. The SH sample exhibits the lowest residual phase content (primarily Mg 2 Si and Fe-containing phases), while the RH sample shows the highest, including additional θ-Al 2 Cu and S-Al 2 CuMg phases. Heating process also affects Mg 2 Si content, with RH sample showing the lowest. Furthermore, heating process significantly influences the distribution and size of dispersoids, including E-Al 18 Mg 3 Cr 2 , Al 6 Mn/Al 6 (Mn, Fe) and L1 2 -Al 3 Zr. SH300 treatment can narrow the dispersoid free zones (DFZs) near grain boundaries. Away from grain boundaries, E, Al 6 Mn/Al 6 (Mn, Fe) and Al 3 Zr phases are present in all samples. Among these dispersoids, the E phase is least sensitive to heating method, whereas Al 6 Mn/Al 6 (Mn, Fe) coarsens significantly under RH. The L1 2 -Al 3 Zr is smallest after SH treatment but coarsens under both RH and SH300 conditions. Additionally, the η phase exhibits a significant coexistence relationship specifically with the E phase, which remains stable even after 465 °C/20 h, thereby delaying the dissolution of η. Although the RH sample contains the highest residual phases, coarse dispersoids, and DFZs within the grain interiors, this only results in a slight decrease in strength and has no detrimental effect on elongation. These findings elucidate phase transformations under varying homogenization heating methods and provide references for optimizing mechanical properties in Al-Zn-Mg-Cu alloys.