Evolution of Deformation Substructure and MgxZnyCaz Metastable Phase in Fine-Grained Mg Alloys

Abstract

The spray-deposition was used to produce billets of Mg-4Al-1.5Zn-3Ca-1Nd (A alloy) and Mg-13Al-3Zn-3Ca-1Nd (B alloy), and evolution of deformation substructure and Mg_xZn_yCa_z metastable phase in fine-grained (3 μm) Mg alloys was investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and electron backscattered diffraction (EBSD). It was found that different dislocation configurations were formed in A and B alloys. Redundant free dislocations (RFDs) and dislocation tangles were the ways to form deformation substructure in A alloy, no RFDs except dislocation tangles were found in B alloy. The interaction between nano-scale second phase particles (nano-scale C15 and β-Mg₁₇(Al, Zn)₁₂ phase) and different dislocation configurations had a significant effect on the deformation substructures formation. The mass transfer of Mg_xZn_yCa_z metastable phases and the stacking order of stacking faults were conducive to the Mg-Nd-Zn typed long period stacking ordered (LPSO) phases formation. Nano-scale C15 phases, Mg-Nd-Zn typed LPSO phases, c/a ratio, β-Mg₁₇(Al, Zn)₁₂ phases were the key factors influencing the formation of textures. Different textures and grain boundary features (GB features) had a significant effect on k-value. The non-basal textures were the main factor affecting k-value in A alloy, while the high-angle grain boundary (HAGB) was the main factor affecting k-value in B alloy.