Improving the dispersoid distribution and recrystallization resistance of a Zr-containing 6xxx alloy using two-step homogenization

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.

KEYWORDS:

• Al-Mg-Si 6xxx alloy
• homogenisation treatment
• Zr-bearing dispersoids
• flow stress
• recrystallization resistance

Acknowledgments

The authors would like to acknowledge the financial support of the Natural Sciences and Engineering Research Council of Canada (NSERC) under the grant number CRDPJ 514651–17 and Rio Tinto Aluminum through the Research Chair in the Metallurgy of Aluminum Transformation at University of Quebec at Chicoutimi.

Disclosure statement

No potential conflict of interest was reported by the author(s).