Study On Hot Deformation Behavior Of Mg₂B₂O₅Whisker Reinforced Magnesium Matrix Composite

The high temperature compression and hot extrusion behaviors of Mg₂B₂O₅whisker with low volume fraction reinforced AZ31B magnesium matrix compositewhich fabricated by stir casting, were investigated in this paper. The opticalmicroscope （OM）, scanning electronic microscope （SEM） and transmission electronicmicroscope （TEM） were applied to characterize the microstructure of the compositeafter hot deformation and to study the evolution of whisker and matrix during hotdeformation. The X-ray diffraction was employed to measure the texture developmentduring hot extrusion. And the tensile properties at room temperature of theas-extruded materials were investigated by tensile testing machine.The high temperature compression behaviors of Mg₂B₂O₅w/AZ31B magnesiummatrix composites at different temperatures and strain rates were studied. The resultsshowed that the peak stress and peak strain which corresponding to the peak stress,both decreased with increasing temperature and increased with the increase of strainrate due to the influences of hard working, dynamic crystallization （DRX） andwhisker. In present study, it was found that the hyperbolic sine law can be applied atgeneral stress. However, the exponential and power laws break down at low and highstress, respectively. The analysis suggests that the deformation mechanism is latticediffusion controlled dislocation climb.Microstructure observations of the Mg₂B₂O₅w/AZ31B magnesium matrixcomposites after high temperature compression showed that the evolution of themicrostructure was closely related to deformation temperature, strain rate anddifferent strains. It was found that the microstructure of the composites aftercompression has twinning, DRX and both mixed. The evolution of the microstructurewas affected by deformation temperature, strain rate, strains and whisker. The affectsof the whisker on matrix microstructure include two aspects: first, the whiskerinhibits the dislocation motion and improves the dislocation density near the whisker,which contribute to an improvement to the nucleation ratio of recrystallization;second, dislocation pile up near whisker resulting stress concentration at lowtemperature with high strain rate, which can initiate twinning. AZ31B alloy and Mg₂B₂O₅w/AZ31B composites with different volume fractionsrods with good surface quality and excellent properties were extruded successfully.DRX took place during hot extrusion, leading to recrystallization behavior and themicrostructure is fine equiaxed grains. The grain size in composites was finer thanalloy indicating that the whisker can stimulate the recrystallization. Hot extrusion canimprove whisker distribution and result in a directional alignment of whisker incomposites. Breakage of whiskers was observed as whisker volume fractionincreasing.The （0002） basal planes of extruded rods are almost parallel to the extrusiondirection indicating that fiber texture is formed during the hot extrusion of AZ31Balloy and magnesium matrix composites. The main component of texture is notmodified on the presence of the Mg₂B₂O₅whisker, however, the intensity of texturedecreases as the reinforcement volume fraction increases. The mechanical propertiesof composites were improved by hot extrusion. However, the mechanical propertiesof composites did not increase monotonically with the volume fraction of whiskers. Itwas found that the tensile and yield strength were the highest when the whiskercontent volume was3.5%, and the elongation was the largest when the whiskercontent volume was1%.