Evolution of Fe-bearing phases during the fabrication and its effect on the mechanical properties of AA8014 aluminum alloy

Abstract

The morphology of Fe-bearing phase particles has significant influences on the mechanical properties of AA8014 aluminum alloy sheets. This study aims to investigate the evolution of the morphology, size, and distribution of Fe-bearing phases during casting, homogenization, and rolling. In the paper, the effects of thermal treatment and deformation on the evolution of the Fe-bearing phases, and the mechanical properties of AA8014 aluminum alloy annealing sheet have been studied quantitatively. The main phase components in the ingot are α-Al matrix, Al6(Fe,Mn), and a small amount of Al3(Fe,Mn) and α-Al(Fe,Mn)Si. Homogenization at 630℃ for 12 h leads to the transformation of the metastable Al6(Fe,Mn) particles into stable α-Al(Fe,Mn)Si with “pore structures”. Subsequent hot rolling (75.0 mm to 7.0 mm, deformation rate of 91%) results in a significant increase in the area number density of Fe-bearing particles, accompanied by a notable decrease in average length and aspect ratio, leading to a more uniform distribution of Fe-bearing phases. Cold rolling (7.0 mm to 0.7 mm, deformation rate of 90%) or further annealing causes slight changes in the area number density and size of Fe-bearing phases. Notably, the content of α-Al(Fe,Mn)Si is minimal in the non-homogenized ingot. After hot rolling and cold rolling, the coarse Fe-bearing particles are observed in the non-homogenized sheets with 7.0 mm and 0.7 mm thickness, with a non-uniform distribution of the Fe-bearing phases. A comparative study was conducted on the mechanical properties and microstructure in final sheets with 0.7 mm thickness fabricated from homogenization and non-homogenization. The yield strength, ultimate tensile strength, elongation, and work hardening exponent in sheet with homogenization are higher due to smaller grain and Fe-bearing phase particles.