Research On The Technology Of Particulate Reinforced Magnesium Matrix Composites Based On Squeeze Casting

The development and application of magnesium alloys in areas such as aerospace,automotive and electronics make a sharp increase in demand for high quality magnesiumalloys at home and abroad. But the disadvantages such as low hardness, low strength, lowelastic modulus and poor wear resistance obviously limit the wide application of magnesiumalloys. However, particulate reinforced magnesium matrix composites can reduce oreliminate these insufficient. SiCphas high hardness, good wear resistance, antioxidation,good thermal shock resistance and extensive sources. Meanwhile, it possesses good physicalwettability and chemical stability with AZ91D magnesium alloy. So magnesium matrixcomposites reinforced by SiCppossess the prospect for industrial scale production. Squeezecasting has advantages such as simple manufacturing process, convenient operation and lowcast. At the same time, it can make magnesium alloys casting possess fine texture and bettermechanical property. Moreover, heat treatment can obviously refine the grain size ofmagnesium alloy casting and further improve its comprehensive mechanical properties.In this paper, SiCp/AZ91D magnesium matrix composites were prepared by squeezecasting with a matrix of AZ91D magnesium alloy and a reinforcing agent of SiCp(the averagesize of SiCpis0.5μm, the addition of SiCpis1wt%). Then some magnesium alloy castingwere treated by solution and aging treatment. The experimental results were studied by Opticsmicroscope (OM), Scan electron microscope (SEM), X ray diffraction appearance (XRD), etc,in order to determine the suitable parameters of squeeze casting and the necessity of rotatingimpeller degassing with Ar.The experimental results show that after adding1wt%SiCpin melted AZ91Dmagnesium alloy, the grains can be obviously refined. This is because SiCpnot only can beused as the fundamental of heterogeneous nucleation, but also easily aggregate in the grainboundaries with the lapse of solid-liquid interface. After heat treatment, with someβ-Mg17Al12phases disappearing and some precipitating well, the grains can be further refined, the average grain size of which reduces to less than100μm and the defects such as shrinkageporosity and blowhole decrease. In addition, SiCpdistributes well, its feature relativelycomplete and the obvious cluster phenomenon does not exist in tissue. The rotating impellerdegassing with Ar can not only remove the impurity of melt but also make SiCpfurtherdistribute well. Furthermore, SiCpcan combine well with AZ91D matrix interface ofSiCp/AZ91D magnesium matrix composites, which are prepared by squeeze casting. Thecleavage fracture, tearing ridge and dimple with small size can be seen on fracture surfaceswhich belong to mixed fracture of toughness and brittleness.The mechanical properties of SiCp/AZ91D magnesium matrix composites prepared bysqueeze casting are significantly improved. When the extrusion force is100MPa, the pouringtemperature is720℃, the mold shell temperature is200℃and the dwell time is20s, itstensile strength and elongation reaches180MPa and2.4%. The tensile strength and elongationof SiCp/AZ91D magnesium matrix composites prepared by squeeze casting are superior toSiCp/AZ91D and AZ91D magnesium matrix composites prepared by gravity casting increasedby27.7%,100%and25%,72%respectively. After the rotating impeller degassing with Ar,the tensile strength of SiCp/AZ91D magnesium matrix composites prepared by gravity castingincreases by16.3%and the tensile strength and elongation of SiCp/AZ91D magnesium matrixcomposites prepared by squeeze casting reaches167MPa and2.36%. Moreover, with therotating impeller degassing with Ar, the tensile strength and elongation of SiCp/AZ91Dmagnesium matrix composites prepared by squeeze casting reaches by29.4%and148.3%after heat treatment.