Effect of Sr on hot deformation behavior and microstructure of Al-4.6Mg alloy

Abstract

The hot deformation behaviors of Al-4.6Mg and Al-4.6Mg-0.2 Sr alloys at temperatures of 300–450 ℃ and strain rates of 0.001–1 s−1 were comparatively studied. Optical microscopy (OM), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) were used to study the effect of Sr on the microstructures of the alloys. The constitutive equations of Al-4.6Mg and Al-4.6Mg-0.2 Sr alloys were established. The apparent activation energies of the two alloys were 165.632 and 157.456 kJ/mol, respectively. The microscopic analysis showed that Sr had no significant effect on the grains of the as-cast Al-4.6Mg alloy, the precipitation phase changed, and the needle-like Al4Sr phase was formed. During isothermal compression (IC), both alloy samples consisted of slender grains and new quasi-equiaxed grains. Compared with the Al-4.6Mg alloy, the Al-4.6Mg-0.2 Sr alloy had a lower LnZ value, a smaller grain size, and more sufficient dynamic recovery (DRV); in addition, the grain growth of the Al-4.6Mg-0.2 Sr alloy was suppressed. The main textures of the Al-4.6Mg alloy were Goss and cubic textures, which were replaced by cubic and brass textures after adding Sr. During the IC of the Al-4.6Mg-0.2 Sr alloy, a nanoscale precipitated τ phase, which was uniformly distributed inside spherical grains, was formed.