Tailoring microstructure and mechanical properties of Al-Mg-Si-Cu alloy with varying Mn and/or Cr additions

Abstract

Introducing and maintaining the subgrain structure during thermomechanical processes is an effective approach to mitigate the strength-ductility contradiction of Al-Mg-Si-Cu alloys, which holds significant importance for their engineering application. The objective of this work is to explore the effects of individual and synergistic additions of two dispersoid-forming elements, Mn and Cr, on microstructure and associated mechanical properties of an Al-Mg-Si-Cu alloy. The results show that when compared to alloys with individual addition of either Mn or Cr, their synergistic incorporation leads to an improved dispersoid precipitation with reduced size. For instance, the 0.7Mn0.4Cr alloy exhibits a number density of 10.26 μm-2, which is twice that of the sum of 0.7Mn and 0.4Cr alloys. In response to that, the 0.7Mn0.4Cr alloy attains enhanced resistance to recrystallization, leading to a well-maintained recovery structure and exceptional mechanical properties. But an excess addition of Cr will result in the formation of primary Al45Cr7 phase, which significantly deteriorate the mechanical properties of the alloy. While notably, the 0.4Cr alloy surprisingly exhibits better recrystallization resistance compared to the 0.7Mn alloy, despite having larger dispersoid size and lower number density. This can be attributed to the coherent interface between the α-Al(Cr,Fe)Si dispersoids and matrix, providing higher pinning force that effectively impede the recrystallization.