Microstructure, tensile and bending properties of extruded Al–Mg–Si 6xxx alloys with individual and combined additions of Zr and Mn

Abstract

This study investigates the effects of individual and combined additions of Mn and Zr on the microstructure, extrudability, tensile and bending properties of extruded Al–Mg–Si 6xxx alloys processed under different homogenization and extrusion conditions. The overall mechanical performances of three alloys are compared and ranked based on the yield strength, bend angle, and bending anisotropy. The results show that compared with an individual addition of Mn or Zr, a combined addition of Mn and Zr (alloy MnZr) results in a higher number density and volume fraction of two types of Mn- and Zr-bearing dispersoids. In the as-extruded condition, the best overall mechanical performance is demonstrated after homogenization at 400 °C and extrusion at 500 °C, particularly for alloy MnZr. After a T5 treatment, alloy MnZr homogenized at 550 °C exhibits a higher yield strength and better bendability than single Mn or Zr additions or other processing conditions. In contrast, the alloy with an individual addition of Zr exhibits an inferior mechanical performance under most processing conditions. The best overall mechanical performance is achieved by alloy MnZr in both as-extruded and T5 conditions.