Alignment and strengthening effect of β′ precipitates in Mg-Gd-Y-Zr during ageing process studied by HAADF-STEM and GPA

In the present study, the structural evolution of the precipitates in Mg-Gd-Y-Zr alloy is investigated by means of high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). The linearly aligned morphology of β′ phases connected by bridging βM phase in one of the three equivalent crystal directions of [101¯0] is formed from defect-free randomly distributed β′phases. Considering the significant strengthening effect of β′ precipitates, a novel perspective of investigating the induced strain field measured by geometric phase analysis (GPA) is conducted. The reducing value of the strain field accounts for a slight decrease in hardness after peak-ageing. Merging and rearrangement of β′ precipitates are found to release the strain field.