Research On The Microstructure And Mechanical Properties Of Mg-5Al-2Ca Alloy Controlled By Low Content SiCp

SiCp/Mg-5Al-2Ca with low volume fractions?1vol.%?and three size of 1?m,5?m and 10?m were fabricated by stir casting.Then the as-cast Mg-5Al-2Ca alloy and SiCp/Mg-5Al-2Ca were subject to hot extrusion.The influence mechanism of SiCp on the Al₂ Ca phase's nucleation and growth has been revealed.While,the microstructures and mechanical properties of SiCp/Mg-Al-Ca after extrusion were investigated,in order to illustrate the coordinate effect of SiCp and Al₂ Ca phase on dynamic recrystallization?DRX?,and the coordinate strengthening effect of SiCp and Al₂ Ca phase.The results indicate that addition of only ¹vol.% SiCp affects the network distribution of Al₂ Ca phase in the as-cast Mg-5Al-2Ca alloy,which can refine the Al₂ Ca.The surface energy increases with decreasing particle size,which can affect the nucleation sites of Al₂ Ca.Meanwhile,the nucleation site of Al₂ Ca phase strongly depends on SiCp size.Al₂ Ca phase precipitate at the boundary of grains.However,Al₂ Ca phase nucleates at 5?m and 10?m of SiCp.When the SiCp size decreases to 1?m,it nearly covers the whole particle.As the decrease of SiCp,the volume fraction of SiCp increases,which significantly refines the grain size of Mg-5Al-2Ca alloy.Hot extrusion significantly refines the grain size of Mg-5Al-2Ca alloy because of the DRX.With the increase of extrusion temperature and speed,the dynamic recrystallization?DRX?grain size increases and DRX proceeds until it completed.After extrusion,the Mg-5Al-2Ca alloys form a typical basal texture,the intensity of which increases as the increase of extruded temperature and decrease of extruded speed.The Al₂ Ca phase distributed with the network in the as-cast conditions are broken up into fine particles which are elongated along the extruded direction in the as-extruded Mg-5Al-2Ca alloy.When extruded at 300? and 0.3mm/s,the Mg-5Al-2Ca alloy exhibits the best mechanical properties,which is affected by grain boundary strengthening,texture strengthening and second phase strengthening.Compared with Mg-5Al-2Ca alloy,the as-extruded SiCp/Mg-5Al-2Ca exhibit finer DRX grain?higher DRX volume fraction and lower basal texture.The addition of low content SiCp leads to finer Al₂ Ca phase and improves the distribution of Al₂ Ca paticles.After extrusion,the Al₂ Ca phases precipitated on the SiCp in the as-cast conditions are broken up into fine particles in the asextruded SiCp/Mg-5Al-2Ca.The fracture of Al₂ Ca phase is different as the variation of SiCp size.No large Al₂ Ca phase is found along 10?m SiCp.As the SiCp size decreases to 1?m,Al₂ Ca still cover the whole particle.The addition of SiCp improves the YS and UTS of Mg-5Al-2Ca alloy,and the main reason are 1)the finer grain size because of DRX;2)the smaller Al₂ Ca particle refined by extrusion.As the decrease of SiCp size,the YS of SiCp/Mg-5Al-2Ca increase and the elongation decrease.The 5?m SiCp/Mg-5Al-2Ca exhibits the highest UTS.