Substantial improvement in cold formability of concentrated Mg–Al–Zn–Ca alloy sheets by high temperature final rolling

Abstract

Poor formability at room temperature (RT) has been the main bottleneck for a wider range of applications of concentrated Mg–Al–Ca(–Zn) sheet alloys. Here, we report that RT stretch formability of concentrated Mg–Al–Zn–Ca alloy sheets can be improved substantially by increasing the final rolling temperature. A Mg–6Al–1Zn–1Ca alloy sheet subjected to 510 °C final rolling shows an index Erichsen (I.E.) value of 7.9 mm, which is significantly higher than that of the same sheet subjected to 450 °C final rolling (4.1 mm). More excitingly, 510 °C final rolled Mg–6Al–1Zn–2Ca (wt%) alloy sheet exhibits a large I.E. value of 8.0 mm which has never been achieved in 2 wt% Ca-containing Mg alloys. A systematic microstructural investigation indicates that the substantial improvement in stretch formability of Mg–6Al–1Zn–xCa (x=1, 2) alloy sheets is mainly associated with weakened basal textures. To clarify the mechanisms responsible for the weak basal textures developed in the high temperature rolled sheets, electron backscatter diffraction (EBSD) assisted slip trace analysis and quasi-in-situ EBSD method were employed. EBSD-assisted slip trace analysis on the side surface of as-rolled Mg–6Al–1Zn–1Ca alloy sheets indicates that the activity of pyramidal <c+a> slip increases significantly by increasing the final rolling temperature from 450 to 510 °C. During subsequent annealing, grains deformed by pyramidal <c+a> slip evolve into new recrystallized grains with a wide spectrum of orientations, which plays a key role in the development of the weaker basal texture.