Influence of Mn and Zn addition on the formation of dispersoids and mechanical properties of Al-Mg-Sc-Zr alloys

Abstract

The effects of the individual and co-addition of Mn and Zn elements on the precipitation of Al₃(Sc, Zr) dispersoids, recrystallization resistance and mechanical properties of Al-Mg-Sc-Zr alloy were studied using scanning electron microscopy, transmission electron microscope, first-principles calculation and tensile testing. The results show that although Mn and Zn could not penetrate in the Al₃(Sc, Zr) dispersoids, these two elements can shift the L1₂-Al₃(Sc, Zr) solvus towards higher Sc concentrations and thus inhibit the precipitation of Al₃(Sc, Zr) dispersoids. Except for the Al₃(Sc, Zr), high density of Al(Fe, Mn)Si dispersoids are formed in the Mn-added alloys, provides additional strengthening effect. The recrystallization resistance is slightly improved after Mn or Zn addition owing to the formation multiple dispersoids or the sluggish grain boundary migration induced by solute Zn atoms. Both of the Mn and Zn addition can improve the strength but decrease the elongation of the Al-Mg-Sc-Zr alloy, the effect of Mn in increasing the strength is much stronger than Zn, and the combined Mn, Zn addition does not show clear advantage compared with individual Zn addition, suggesting superior advantage of the Mn addition in this alloy. The main reason is due to the synergistic enhancement of the dispersion strengthening of the Al(Fe, Mn)Si and Al₃(Sc, Zr) dispersoids. This result provides in insight in the development new low-Mg content Al-Mg-Sc-Zr alloys with high properties.