Study On AZ31 Magnesium Alloy And TiCp/AZ31 Magnesium Matrix Composites By Equal Channel Angular Extrusion

The microstructure and mechanical properties due to equal channel angular extrusion (ECAE) were investigated using electromagnetic continuous cast AZ31 magnesium alloy and self-propagating synthesized TiCp/AZ31 magnesium matrix composites. By means of mechanical testsing, optical microscope and transmission electron microscopy (TEM), this study identied some behaviors and mechanisms that influence final properties of AZ31 and TiCp/AZ31 during ECAE such as grain refinement mechanism, fracture mechanism. Fracture surfaces were characterized using scanning electronic microscopy (SEM). The basal plane texture was measured qualitatively by the X-ray diffraction.The experimental results showed that the grains of AZ31 alloy were dramatically refined after ECAE 4 passes and the microstructures consisted of equiaxed recrystallized grains. Grain refinement could be attributed to continuous dynamic recovery and recrystallization. At the same temperature, the elongation of ECAE processed AZ31 alloy increased with increasing passes, whereas the yield strength decreased. In contrast, when sujected to same strain, the yield strength of ECAE processed AZ31 increassed with increasing the deformation temperature, but the elongation decreased. After two-step ECAE, the grain size was refined to 1.7μm and higher dislocation density and subgrain boundaries were observed. Compared with the as-extruded AZ31 magnesium alloy, both the yield strength and elongation were improved after two-step ECAE. Dislocations were generated at the initial stage of ECAE and come together to form subgrain boundaries during deformation. The new generated dislocations were subsumed in subgrain boundaries. As deformation proceeds, the misorientation between subgrain boundaries which gradually evolved to low angle grain boundaries and high angle grain boundaries.The ECAE deformation of TiCp/AZ31 at room temperature was inhomogenous due to the presence of TiC particle. The grains around the particle were refined significantly. The inhomogeneity and the distribution of TiC particle were improved with increasing passes. Compared with the as-extruded TiCp/AZ31, the yield strength of TiCp/AZ31 was improved but the elongation decreased after ECAE 1 pass. With the increase of extrusion passes, the yield strength decreased but the elongation was improved.The wear behavior of the TiCp/AZ31 magnesium matrix composites was also investigated and the results showed that the friction and wear curve was unstable that could be due to the inhomogeneous distribution of TiC particle. After ECAE 1 pass the average wear coefficient decreased. As the passes increased, the friction and wear curve became more stable and the average wear coefficient decreased to 0.23.