Study of basal < a > and pyramidal < c + a > slips in Mg-Y alloys using micro-pillar compression

ABSTRACT

The effect of yttrium (Y) on the critical resolved shear stresses (CRSS) of < a > basal slip, $\left\{10\overline{1}2\right\}⟨\overline{1}011⟩$ tension twinning and < c + a > pyramidal slip has been studied using micro-pillar compression tests along selected orientations at room temperature, on two magnesium (Mg) alloys with different Y contents (0.4 and 4 wt.%). The CRSS of < a > basal slip increased slightly from 30 ± 1 MPa (for Mg-0.4Y) to 37 ± 3 MPa (for Mg-4Y). In Mg-0.4Y, the resolved shear stress to activate the $\left\{10\overline{1}2\right\}⟨\overline{1}011⟩$ tension twin was determined to be 45 ± 12 MPa, while in Mg-4Y it was 113 MPa. The compressed samples were studied using scanning electron microscopy (SEM), transmission Kikuchi diffraction (TKD) and transmission electron microscopy (TEM). It was found that < c + a > dislocations slip mainly on $\left\{\overline{1}\overline{1}22\right\}$ (Pyra II) planes with a CRSS of about 119 MPa in Mg-0.4Y and slip mainly on $\left\{0\overline{1}11\right\}$ (Pyra I) planes in Mg-4Y with a CRSS of 106 MPa. There is a significantly lowered CRSS ratio between < c + a > slip and < a > basal slip in both alloys (2.8 and 4.8) compared with that reported in bulk pure Mg (∼100). The easy activation of < c + a > on Pyramidal I slip is expected to promote the frequent cross-slip in Mg-4Y alloy.

KEYWORDS:

• Mg-Y
• micro-pillar compression
• CRSS
• pyramidal slip
• twinning

Acknowledgement

The authors would like to thank Professors Mike Loretto and Ian Jones for helpful discussions on the paper.

Disclosure statement

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

Additional information

Funding

The authors acknowledge the support from the Engineering and Physical Science Research Council for funding (EP/L017725/1) for some facilities used in this work.