Effect of SiCp volume fraction on microstructure and properties of powder metallurgy SiCp reinforced aluminum matrix composites

Aluminum matrix composites (AMCs) with SiCp volume fraction of 2.5% and 5% were prepared by ball milling, powder mixing-cold pressing, sintering and hot extrusion using 1 mu m SiCp and 7000 series aluminum alloy powders. The phase analysis and microstructure observation of composite extruded materials were carried out by metallographic microscope, x-ray diffraction (XRD) and scanning electron microscopy(SEM). The main properties of the composites including density, electrical conductivity and compressive mechanical properties were tested. The results show that SiCp is uniformly distributed around the particles of aluminum matrix in the AMCs fabricated by Argon sintering-hot extrusion. And when the volume fraction of SiCp increases from 2.5% to 5%, the grain size of the composite becomes smaller and the dislocation strengthening increases with the increases of volume fraction of SiCp. Simultaneously, the density and densification of the composites decrease with the increase of the volume fraction of SiCp, and the densification of the composites after extrusion is above 98.5%. The hardness of the composites increases from 192.3 HV to 201.4 HV with the increase of volume fraction of SiCp. The electrical conductivity of the composites also decreases with the increase of the volume fraction of SiCp which may be due to the fact that SiCp is difficult to conduct and hinders the movement of free electrons in the matrix. The compressive strength improves with the increase of the volume fraction of SiCp. When the volume fraction of SiCp is increased from 2.5% to 5%, the compressive strength of the composite in the solution-aging state increases from 668.12 MPa to 683.94 MPa, but the fracture strain decreases from 10.57% to 8.4 %.