Transformation mechanism of yielding behavior in the aged Mg-Gd-Y-Nd-Zr alloy during room temperature tensile deformation

The microscopic mechanism of room-temperature discontinuous yielding in fine-grained Mg alloy is revealed for the first time, highlighting the critical role of mobile dislocations. The yielding behavior transitioned from discontinuous to continuous with increasing aging time. Discontinuous yielding behavior is attributed to partial mobile dislocations within the initial microstructure overcoming obstacles posed by subgrain boundaries and LAGBs during tensile deformation. The mobile dislocations activated under high stress and traversed subgrain boundaries or LAGBs, resulting in a sudden stress drop followed by a stress plateau. After aging for 12 h, the β' phase stabilizes the LAGBs to prevent dislocation crossing them, but still allows some dislocations to cross subgrain boundaries, resulting in a shortened yield plateau. Upon extending aging time to 32 h, high-density β' phases effectively pins dislocations and stabilizes both subgrain boundaries and LAGBs, thereby suppressing dislocation movement and completely eliminating discontinuous yielding.