| Being the lightest available structural metals, magnesium (Mg) alloys have received much attention for application in the aerospace and many other fields. However, poor ductility at ambient temperature limits their industrial applications. In this study, pre-aging treatment and hot compression were carried out on Mg-8Y-2Nd alloy and Mg-2.7Nd-0.5Zn-0.8Zr alloy. The evolution of microstructures during deformation and annealing is observed by optical microscopy and SEM. The texture evolution is examined by electron backscatter diffraction (EBSD) analysis. Tensile ductility at ambient temperature is analyzed.Hot compression tests were performed on Mg-8Y-2Nd alloy at different deformation temperatures and a strain rate of1.0s-1. The effect of pre-aging treatment on the microstructure, texture variation and mechanical properties were investigated. With the increase of deformation temperature, the flow stress decreases gradually, but the flow stress of aging state is always higher than that of solid solution state. And the age state samples present better mechanical properties than the solution state samples when deformed at the same deformation temperature, especially when deformed at793K. The optimized mechanical properties of e age state specimen were220MPa in ultimate tensile strength and18%in fracture elongation. The microstructure with different compression strains at793K was investigated. The Necklace-structure occurred in the solution sample at the early stages of deformation. During the hot compression process, the second phase particles precipitate along the dynamic recrystallization (DRX) grain boundaries and only exist in the DRX zone. The precipitates in solution state sample play an important role in grain refinement. To the age state sample, the large amounts of precipitates hinder the movement of dislocation and promote the non-basal slip. Deform bands were observed at the early stage of deformation. It was found that precipitates produced by pre-aging treatment can be effective in promoting DRX during compression. After deformation, he age state specimen showed a homogeneous and refined structure. A significant decrease in the intensity of the initial texture was observed. This was attributed to DRX of new grains. The new grains exhibited a random texture while the initial grains rotated perpendicular to the compression direction, exhibiting a strong texture. The ductility of the age state specimen was three times higher than solution one, while the ultimate tensile strength was almost doubledHot compression tests were performed on Mg-2.7Nd-0.5Zn-0.8Zr alloy at different deformation temperatures and a strain rate of1.0s-1. Similar results were obtained Both kinds of compressed sample show a completely DRX structure when deformed at the793K, indicating that the difference between the function of the precipitates in two kinds of samples was weakened Annealing treatment was employed after hot compression due to the poor ductility. It was found that solution state sample got a fully recrystallization structure when annealing for1h, while the age state sample only need5min. And the recrystallization grain size of solution state sample is less than the age state sample before annealing1h. Increasing annealing time, solid solution state compression sample grains grow up quickly, the grain size is greater than the age state. The solution state sample got the optimized mechanical properties when annealing for30min, the ultimate tensile strength is210MPa and the elongation to fracture is18%, which is three times higher than the compressed sample without annealing. As to age state sample, the optimized mechanical properties were215MPa in strength and20%in ductility, which is two times higher than the compressed sample without annealing. |
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