Hot deformation behavior of an extruded Mg–Li–Zn–RE alloy

Abstract

A new Mg–7.8%Li–4.6%Zn–0.96%Ce–0.85%Y–0.30%Zr alloy has been developed. α phase, β phase and RE-containing intermetallics formed in the alloy. It is found that the alloy can easily be extruded at 260°C with σ0.2=256MPa, σb=260MPa and δ=14%. Hot deformation behavior of the extruded alloy was studied using the processing map technique. Compression tests were conducted in the temperature range of 250–450°C and strain rate range of 0.001–10s−1 and the flow stress data obtained from the tests were used to develop the processing map. The different efficiency domains and flow instability region corresponding to various microstructural characteristics have been identified as follows: (1) Domain I occurs in the temperature range of 250–275°C and strain rate range of 1–10s−1, with a peak efficiency of about 50% at 250°C/10s−1. Incomplete DRX process has occurred in β phase and DRX process hardly occurs in α phase; (2) Domain II occurs in the temperature range of 250–275̊C and strain rate range of 0.001–0.003s−1, with a peak efficiency of about 42% at 250°C/0.001s −1. Incomplete DRX process has occurred in β phase and α phase; (3) Domain III occurs in the temperature range of 400–450°C and strain rate range of 1–10s−1, with a peak efficiency of about 42% at 450°C/10s−1. Complete DRX process has occurred in β phase and α phase. No cracking, cavity and band of flow localization are observed in flow instability region. The optimum parameters for hot working of the alloy are 250°C/10s−1 and 250°C/0.001s−1, at which fine dynamic recrystallization microstructure will be achieved. RE-containing intermetallics and α phase accelerate the DRX process in β phase. The softer β phase reduces the driving force for DRX process in α phase, so DRX process in α phase is retarded.