Study On The Preparation And Properties Of SiCp/Al Composites Round Rods

In this work,the SiC particles reinforced Al-based（SiCp/Al）composites were prepared by semi-solid stir casting method,and the extrusion die and heating device of the round rods were designed independently.The SiCp/Al composite round rods with high surface quality were extruded by optimizing the extrusion preheating temperature and the structure of the mold and the heating device.Metallographic microscope,scanning electron microscope and energy spectrometer were used to study the microstructure,SiCp distribution,SiCp/Al interface and fracture morphology of composite materials.The mechanical and electrical properties of SiCp/Al composite round rods were tested by microhardness tester,tensile tester and digital bridge.Moreover,it is important to observe and discuss the relationship between microstructure and material properties.The major results could be concluded as follows:The extrusion die and the heating device were designed base on the size of the SiCp/Al composite ingot,and the strength of each component of the mold was checked to ensure the structural stability.The structure of the heating device and the distribution of the heating elements were optimized to achieve smooth extrusion of the round rod in the preheating temperature range of 460°C to 580°C.The surface quality and mechanical properties of pure aluminum rods prepared by different preheating temperature were tested in order to optimize the process parameters of extrusion.As a result,at a preheating temperature of 500°C,the SiCp/Al composite round rod with high surface quality could be obtained.In the as-cast microstructure of SiCp/Al composites,the uniformity of SiCp distribution decreased with the increase of the addition of SiCp content,and the uniformity was higher at the content of SiC particles from 2%to 4%.SiCp were mainly distributed along the grain boundaries,and a few particles were distributed in the grains.As the content of SiCp is above 4%,defects such as particles agglomeration and pores became more serious,and the interface bonding of SiCp/Al was weakened.Compared to cold processing methods,the resistance of deformation of SiCp/Al composites decreased during hot extrusion process.SiCp were distribute more homogenous by applying external forces,moreover,the amount of defects such as shrinkage and porosities decreased and the interface bonding of SiCp/Al increased at the same time.The ultimate tensile strength of SiCp/Al composites with 4%SiCp content was 99.3 MPa,which is29.0%higher than that of pure aluminum rod（77.0 MPa）under the same processing condition.The elongation of extruded composites increased and the lowest electrical resistivity of the extruded composites decreased to 3.05×10^-8Ω·m after annealing treatment,which is approaching the electrical resistivity of pure aluminum rod.In conclusion,the mechanical properties of Al-based composites increased significantly and the electrical resistivity of the composites could remain low in the meantime by the combination of the addition of reinforced particles,hot extrusion processing and annealing treatment.