Effect of Al content on the critical resolved shear stress for twin nucleation and growth in Mg alloys

TL;DR

This study investigates how aluminum content influences the critical resolved shear stress for twin nucleation and growth in magnesium alloys, revealing that higher Al levels significantly increase shear stress and plastic anisotropy.

Contribution

It provides experimental data linking Al content to shear stress for twinning and slip in Mg alloys, confirming and extending theoretical models.

Findings

Al increases shear stress for twin nucleation and growth

Shear stress increase is more pronounced at higher Al levels

Al addition enhances plastic anisotropy in Mg alloys

Abstract

The effect of Al atoms in solid solution on the critical resolved shear stress for twin nucleation and growth was analyzed by means of the combination of diffusion couples with compression tests in micropillars oriented for twinning. The critical resolved shear stress for twin nucleation was higher than that for twin growth and both increased by the same amount with the Al content. Nevertheless, the increase was small ( approx. 10 MPa) for 4 at.%Al but large (up to 60-70 MPa) for 9 at.%Al. These results were in agreement with Labusch-models based on first principles calculations in the dilute regime (< 5 at.%Al) [51]. Comparison with recent data in the literature showed that Al atoms are more effective in increasing the critical resolved shear stresses for twin nucleation and growth than for basal slip [21]. Finally, compression tests in micropillars oriented along [0001] showed the critical shear stress for pyramidal slip increased rapidly with the Al content from 98 MPa in pure Mg to 250 MPa in Mg-9 at.%Al. Thus, the addition of Al increased the plastic anisotropy of Mg alloys.