Microstructure And Mechanical Properties Of AZ31B Mg Alloy Processed With Equal Channel Angular Pressing

The equal channel angular pressing (ECAP) has been performed to the samples from the AZ31B Mg alloy hot rolled plate, and the effects the pressing temperature and pressing path on the microstructure have been investigated. The results of the metallographic analysis and the pole graph analysis show that the original microstructure is the equiaxed grain with the diameter of15μm, and display the strong basal plane texture. After the ECAP the grains are refined obviously, and the basal plane texture is weaken to some extend. The pressing paths have some effect on the grain refinement from the ECAP. After5pass of the ECAP with the path A and BA, the average grain diameter reduce to3.5～3.6μm. Comparing the refining effectiveness of the EACP with different pressing path, the path BC is the most good, with the average grain diameter of3.3μm after5pass, and the path C is not good comparatively. The ECAP has been performed at350℃,375℃and400℃respectively, and the effect of the pressing temperature on the grain refinement has been studied. The results show that the grain refinement degree increase as pressing temperature decreasing in the temperature range from350to400℃.The dynamics analysis on the grain growth has been carry out in order to investigated the tendency of the grain growth. The results show that the thin grains in the AZ31B Mg alloy have obvious growth tendency above the temperature of350℃, and kinetics equations of grain growth at350℃,400℃and450℃are respectively D2=12.27+19.22t D2=10.18+31.43t and D2=13.26+2059.22t.With the temperature increasing, the tendency of the grain growth in the AZ31B Mg alloy increases rapidly. The increment speed of the square of the average grain diameter increases to1.64times when the temperature increases from350℃to400℃, the increment speed of the square of the average grain diameter increases to65.5times rapidly when the heating temperature increases from400℃to450℃.According to the path A, the samples with the (0001) basal plane texture have been extruded with the two different orientations. The first orientation is that the original normal direction of the sample is perpendicular to the plane formed by the extruding channel, and the second orientation is that the original normal direction of the sample is parallel to the plane formed by the extruding channel. The results show that after the samples are extruded with the first orientation the tensile and yield strength in the extruding direction increase slightly with the extruding pass increasing, but the compression yield strength in the transverse direction of the rolled plane decreases obviously. With the extruding pass increasing, the tensile strength in the extruding direction and the compression strength in the transverse direction of the rolled plane decrease slightly but the tensile yield strength and the compression yield strength decrease, after the samples are extruded with the second orientation. On the other hand the extensibilities of the samples extruded according to boththe first orientation and the second orientation increase with increasing the extruding pass.After extruding of5pass, the extensibilities increases from10.9%to17%for the firstorientation, and from10.9%to19.6%for the first orientation. The tension and compressiontests show that the relationship between the grain diameter and the strength of the AZ31B Mgalloy after ECAP do not accord with the Hall-Petch formula, and one of the reasons is thechange of the grain orientation because of the ECAP.