The Effect Of Hot Deformation On Microstructure And Mechanical Properties Of Mg–Al–Ca Alloy And SiC_p/Mg–Al–Ca Composite

The Mg-5Al-2Ca alloys reinforced by 0,2,5 and 10vol.%5μm SiCp, respectively, were fabricated by stir casting. Then the as-cast Mg-5Al-2Ca and SiCp/Mg-5Al-2Ca composites were subject to hot extrusion. The presence of SiCp influence on microstructure and mechanical properties of the as-cast and as-extruded Mg-5Al-2Ca matrix alloys were investigated. By comparing with matrix alloy, revealing that the influence mechanism of SiCp on Al2Ca phase nucleation and growth, SiCp combing with Al2Ca phase on DRX nucleation and growth, and SiCp combing with Al2Ca phase effect on mechanical properties.Research results show that the Al2Ca phase distributed with the network in as-cast conditions were broken up into fine particles which were elongated along the extrusion direction in as-extruded Mg-5Al-2Ca alloy. And the size of Al2Ca particles becomes much smaller with increasing temperature. After extrusion, the Mg-5Al-2Ca alloy formed a typical base surface texture, and the intensity of basal texture increases with increasing extrusion temperature. Even though the average grain size increases as increasing extrusion temperature increased from 573K to 623K, the YS, UTS and elongation of as-extruded Mg-5Al-2Ca alloy are most kept the same at 573K and 623K. The main reason is the result of interaction of refined crystalline strengthening, Al2Ca phase strengthening and texture strengthing at the two temperatures. The working hardening rate of as-extruded alloys does not change monotonously with increasing extrusion temperature, the largest θ value of Mg-5Al-2Ca alloy is obtained when the extrusion was peformed at 623 K.In as-cast Mg-5Al-2Ca alloy, the addition of SiCp disturbs the network distribution of Al2Ca phase. With the increasing volume fraction of SiCp, the reducing of network structure Al2Ca decreases accompanied by the increasing of granular structure Al2Ca. The main reason is that the Al2Ca phase’s nucleation sites increase with the increasing volume fraction of SiCp. By comparing with the as-extruded Mg-5Al-2Ca alloy, the Al2Ca phase and grain size can be further refined by the addition of 2 vol.% SiCp. But the variation of them is unobvious as the SiCp content increased from 2vol.% to 10vol.%. As compared with Mg-5Al-2Ca matrix alloy, the addition of SiCp conduces to obvious improvement of YS, UTS and θ value, however, at the expense of elongation. The UTS of as-extruded SiCp/Mg-5Al-2Ca composite does not change monotonously with increasing SiCp’s content, the highest UTS appears at the volume fraction of SiCp is 5%. For the 5vol.% SiCp/Mg-5Al-2Ca composites extruded at different temperature, the UTS and elongation of it do not change linearly with increasing temperature. The 5vol.% SiCp/Mg-5Al-2Ca composite extruded at 623 K exhibits the largest UTS and elongation. At the first stage of deformation, the work hardening rate (θ) of as-extruded 5vol.% SiCp/Mg-5Al-2Ca composites increases with decreasing extrusion temperature. However, the opposite phenomenon is observed at the end stage of deformation.By comparing with as-extruded Mg-5A1 alloy, the as-extruded Mg-5Al-2Ca alloy exhibits better high temperature mechanical property, the main reason is that there is high melting point and stable Al2Ca phase. During tensile test at different temperatures, the as-extruded Mg-5Al-2Ca alloys show the different fracture characteristics and mechanisms. The addition of SiCp improved the high temperature strength of the matrix alloy, and the high temperature strength increased as the increasing SiCp’s content.