Effect of heating processes during homogenization on the microstructure evolution of Al-Zn-Mg-Cu alloy

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.