The Study On Preparation Of Al₂O_3sf/AZ91D Composite And Equal Channel Angular Pressing Shear Deformation

In this paper, wet mixture method was employed to prepared precast blocks of Al₂O₃ short fiber, whose volume fraction was 5%. Technological parameters affecting the forming, structures, strength of precast block, was also researched. 5vol.%Al₂O₃sf/AZ91D magnesia based composite was prepared by liquid infiltration with low pressure. 5vol.%Al₂O₃sf/AZ91D magnesia based composite, for the first time, was also extruded with equal channel angular pressing (ECAP). SEM was employed to observe the microstructures of 5vol.%Al₂O₃sf/AZ91D magnesia based composite. Mechanical properties of magnesia based composite was tested by tension experiments of elevated temperature and room-temperature. Tension fracture was analyzed by SEM. Fracture mechanism of magnesia based composite was also researched.Precast blocks with homogeneous structures and enough strength were prepared successfully, which laid a path for preparing precast blocks with low volume fraction. 5vol.%Al₂O₃sf/AZ91D magnesia based composite was prepared at 750℃pouring temperature and at 550℃die preheat temperature. Precast blocks have been infiltrated by low pressure when pourability of metal fused mass was good. During infiltration, metal fused mass not only infiltrated enough, but only needed to be imposed on high pressure. If pressure is not enough, the mechanical properties of magnesia based composite was low because of deficiencies, such as shrinkage cavity and rarefaction. Although the strength and plastic properties of magnesia based composite was inferior, the magnesia based composite was extruded by ECAP. During the ECAP, the extrusion temperature and the extrusion rate of speed were important. In this study, the extrusion temperature and the extrusion rate of speed were 350℃and 0.5-0.6 mm/s. Hydrostatic pressure was employed to ECAP.Both the microstructures and mechanical properties have been improved after ECAP. The analyses of fracture has also indicated strengthen body has inhibited the expansion of crack.