Effect of Zn Content on the Microstructure and Mechanical Properties of Extruded T6-Treated Al-1.5Mg-1Si-0.6Mn-xZn Alloys

Abstract

Based on an Al-1.5Mg-1Si-0.6Mn alloy, the effect of Zn addition on the microstructure, phase constitution and mechanical properties of T6-treated alloys was investigated by varying the nominal Zn content from 0 to 3.6 wt.%. The results show that the microstructure of the alloys with different compositions is mainly composed of the α-Al matrix, Mg 2 Si or Mg-Si-rich phases and Al(Fe,Mn)Si phases. With increasing Zn content, the extent of Zn solid solution and segregation in the matrix and fine precipitate-enriched regions increases, accompanied by the formation of MgZn 2 -related nanoscale precipitates or solute-rich regions. Zn addition markedly enhances the age-hardening response: the Vickers hardness increases from 81.22 to 97.50 HV, while the ultimate tensile strength and yield strength increase from 237.40±5.07 MPa and 176.10±2.23 MPa to 283.20±10.93 MPa and 232.57±9.82 MPa, respectively. The alloy with the highest Zn content (3.6 wt.% nominal) achieves the highest strength among the compositions investigated in this study while retaining an elongation of 20.28±1.71%, indicating a favorable strength-ductility balance. The strengthening effect of Zn is mainly attributed to solid-solution strengthening and Mg-Si/Mg-Zn-related precipitation strengthening, whereas coarse Mg 2 Si or Mg-Si-rich and Al(Fe,Mn)Si particles act as preferential microvoid nucleation sites and thereby affect ductility and fracture behavior.