The evolution of microstructure and texture of AZ80 and AZ80-LaMM magnesium alloy wheel hubs processed by single-pass radial forging

Abstract

In this paper, 1.5 wt% La-rich Mish Metal (LaMM) was added to AZ80 magnesium alloy, and microstructure evolution, texture development of AZ80 wheel hub were studied by single-pass radial forging, so as to provide basic data for the preparation of magnesium alloy wheel hub with uniform microstructure and excellent mechanical properties. A detailed microstructure analysis was performed using the optical microscopy (OM) and electron back-scatter diffraction (EBSD). The result shows that the LaMM greatly improves the refinement ability and deformation uniformity of AZ80 wheel hub, and the volume fraction of DRX is greatly increased, which is attributed to the increase of recrystallized nucleation cores in the RE (rare earth) phase bands through the effect of particle stimulated nucleation (PSN). The texture of the wheel hub is gradually weakened along the forming direction due to the increasing strain and dynamic recrystallization (DRX) degree. The larger cumulative strain can promote the activation of the non-basal slip systems and the generation of dislocations, which ultimately promotes the emergence of dynamic recrystallized (DRXed) grains and weakens the texture. The texture of AZ80 wheel hub is weakened by LaMM, which changes the DRX mechanism of spokes and lower rim part, promotes the occurrence of DRX, and produces more non-basal slip. Some of the grains are biased towards the basal plane, which is more conducive to grain slip, while the other DRXed grains are also deflected due to non-basal plane slip. The hardness values of AZ80-LaMM wheel hub are larger and more uniform than those of AZ80 wheel hub. This can be attributed to the fact that the RE phases inhibit the grain growth, keep the microstructure stable and produce better grain refinement.