Improving the dispersoid distribution and recrystallization resistance of a Zr-containing 6xxx alloy using two-step homogenization
Ali Elasheri, E. M. Elgallad, Nick Parson, X.- G. Chen
Abstract
Two-step homogenisation was applied to a 6xxx alloy containing Zr to enhance the characteristics of Zr-bearing dispersoids and recrystallization resistance. The two-step homogenisation treatments were composed of a first step at 400 °C for 48 h and a second step at 500 °C for 2 and 5 h and compared with single-step homogenisation conducted at 500 °C for 2 and 5 h. The dispersoid microstructure was characterised using optical microscopy and scanning and transmission electron microscopies. The thermomechanical simulator Gleeble 3800 was used to conduct the hot compression tests at 350°C/1.0s−1. To study the recrystallization resistance, post-deformation annealing at 500 °C for 1 h was performed on the deformed samples. The grain structure after deformation and annealing was characterised based on the EBSD technique. The results showed that compared to single-step homogenisation, the dispersoid characteristics were significantly improved using two-step homogenization, where the number density of L12-Al3Zr dispersoids increased by 75–145% while their size decreased by 9–25% and the distribution of the DO22-(Al, Si)3(Zr,Ti) dispersoids became more uniform. The improved characteristics of Zr-bearing dispersoids and the narrower dispersoid-free zones produced by the two-step homogenization significantly improved the recrystallization resistance with a reduction in the recrystallized area fraction reached 85% when compared with single-step homogenisation.