Twinning and dislocation slip behavior of VW75 alloy at room temperature compression

The VW75 alloy (Mg-7Gd-5Y-1Nd-0.5Zr) is a high-strength, heat-resistant Mg-RE alloy successfully applied in aerospace field. The elongation of this alloy is only 5%, so it is necessary to investigate the deformation mechanisms of this alloy to regulate its comprehensive performance. Herein, the compressive deformation behavior of VW75 was systematically investigated across strains of 4%, 6%, 8% and 10% utilizing EBSD and TEM. The study reveals an anomalous dominance of {11-21} tensile twins over the conventional {10-12} extension twins for all strain states. {10-12} twins exhibited transverse extension and merging, whereas {11-21} twins maintained a stable, fine lamellar structure. Dislocation analysis confirmed a strain-dependent transition from predominant basal <a> slip to the simultaneous activation of <a>, <c>, and <c+a> dislocations at higher strains. A critical divergence in variant selection criteria was identified: {10-12} twinning adhered to the Schmid factor (SF) law, while the activation of certain {11-21} twin variants exhibits a pronounced deviation from the SF criterion. The activation of these low-SF variants is primarily controlled by the geometric compatibility factor (m') with neighboring grains. Furthermore, the observed crossing-like twin-twin junctions between {11-21} variants act as effective barriers to dislocation motion and promote grain refinement, contributing significantly to the strain hardening capacity of the alloy.