Preparation And Properties Of SiCp/B₄Cp Reinforced AZ91D Magnesium Matrix Composites

Particle reinforced magnesium matrix composites become one of the research hotspots in recent years due to their low cost,easy preparation and processing,as well as certain advantages in mechanical properties.Hybrid magnesium matrix composites with different particles and different sizes are also widely used due to their excellent mechanical properties.In this paper,micron SiC particle reinforced AZ91D magnesium matrix composites(SiCp/AZ91D),micron SiC-micron B₄C hybrid reinforced AZ91D magnesium matrix composites((SiC+B₄C)p/AZ91D)and nano SiC-micron B₄C hybrid reinforced AZ91D magnesium matrix composites((n-SiC+B₄C)p/AZ91D)were prepared by microwave sintering and hot pressing sintering,respectively.The effects of sintering temperature,sintering time and reinforcing phase content on the microstructure and properties of the corresponding composites were studied.The results show that the microstructure of the composite is uniform and density by microwave sintering at 550?for 30min.The magnesium matrix composites of the three systems are mainly composed of?-Mg,Mg₁₇Al₁₂ and the corresponding reinforced phases.With the increase of reinforced phase contents,the relative density of SiCp/AZ91D magnesium matrix composites and(SiC+B₄C)p/AZ91D magnesium matrix composites decreases,the microhardness increases,and the compressive strength increases at first and then decreases.The two kinds of composites both obtain better comprehensive mechanical properties by adding 15%reinforcement phase.Compared with pure AZ91D magnesium alloy,the microhardness and room-temperature compressive strength of 15%SiCp/AZ91D magnesium matrix composites,which vary from79.97 HV and 148.5 MPa to 118.21 HV and 355.2 MPa,increases by 47.82%and139.19%,respectively.The microhardness and room-temperature compressive strength of 15%(SiC+B₄C)p/AZ91D magnesium matrix composites reach 166.16 HV and 326.3MPa,which are 107.78%and 119.73%higher than those of pure AZ91D magnesium alloy,respectively.The wear resistance of the composites can be improved with the decreases of the wear rate by adding appropriate amount of reinforcement phase.The best performance of(n-SiC+B₄C)p/AZ91D composites can be obtained when the ratio of n-SiC to B₄C is 1.5:13.5.Compared with single particle size hybrid reinforcement,its microhardness and room-temperature compressive strength decreases slightly,which are145.1 HV and 275.1 MPa,respectively.While,the wear resistance improves slightly.The microstructure of the composite is uniform and density by hot pressing sintering at 530?for 30min under 30MPa.The magnesium matrix composites of the three systems are still mainly composed of?-Mg,Mg₁₇Al₁₂ and the corresponding reinforced phases.As the content of the reinforcing phase increases,the relative density of the SiCp/AZ91D magnesium matrix composites and(SiC+B₄C)p/AZ91D magnesium matrix composites decreases slightly,but both remains above 98%.At the same time,the microhardness increases and the compressive strength increases first and then decreases.The two kinds of composites both obtain better comprehensive mechanical properties by adding 15%reinforcement phase.Compared with pure AZ91D magnesium alloy,the microhardness and room-temperature compressive strength of 15%SiCp/AZ91D magnesium matrix composites,which vary from 81.52 HV and 300.6 MPa to 183.22HV and 428.3MPa,increases by 124.75%and 42.48%,respectively.The microhardness and room temperature compressive strength of 15%(SiC+B₄C)p/AZ91D magnesium matrix composites reach 195.83 HV and 466.7 MPa respectively,which are 140.22%and 55.26%higher than those of pure AZ91D magnesium alloy.Compared with the matrix,the wear rate of the composites decreases by the addition of reinforcing particles.The(n-SiC+B₄C)p/AZ91D composites can have the best comprehensive performance when the ratio of n-SiC to B₄C is 1.5:13.5.Its microhardness and room temperature compressive strength are 224.58 HV and 459.2 MPa,respectively.Compare with the single particle size hybrid reinforcement,it has the better wear resistance.Compare with microwave sintering,the composites prepared by hot pressing sintering have higher relative density,microhardness,compressive strength,and wear resistance.