Shulin Lü

Effects of ultrasonic vibration on microstructure and mechanical properties of nano-sized SiC particles reinforced Al-5Cu composites

Ultrasonic vibration (UV) treatment has been successfully applied to improve the particles distribution of nano-sized SiC particles (SiCp) reinforced Al-5Cu alloy matrix composites which were prepared by combined processes of dry high energy ball milling and squeeze casting. When UV treatment is applied, the distribution of nano-sized SiCp has been greatly improved. After UV for 1 min, large particles aggregates are broken up into small aggregates due to effects of cavitation and the acoustic streaming. After UV for 5 min, all the particles aggregates are dispersed and the particles are uniformly distributed in the composites. Compared with the Al-5Cu matrix alloy, the ultimate tensile strength, yield strength and elongation of the 1 wt% nano-sized SiCp/Al-5Cu composites treated by UV for 5 min are 270 MPa, 173 MPa and 13.3%, which are increased by 7.6%, 6.8% and 29%, respectively. The improvements of mechanical properties after UV are attributed to the uniform distribution of nano particles, grain refinement of aluminum matrix alloy and reduction of porosity in the composites.

Preparation and properties of nano-SiCp/A356 composites synthesised with a new process

ABSTRACT Nano-SiCp reinforced A356 aluminium alloy composites were prepared by solid–liquid mixed casting. Nano-SiC particles 40 nm in diameter were pre-oxidised at 850°C. Millimetre-sized composite granules were then fabricated by milling a mixture of nano-SiCp and Al powders, and then remelting to form an alloy melt, which was treated by mechanical stirring and ultrasonic vibration to prepare the composites. Results showed that nano-SiC particles were dispersed pretty well within the matrix and no serious agglomeration was observed. As the weight fraction of SiCp increased, the tensile strength, yield strength and elongation of the composites increased as well, by 22%, 62% and 24%, respectively, when compared to A356 alloy with 2wt-% nano-SiCp.

Effects of high-pressure rheo-squeeze casting on the Fe-rich phases and mechanical properties of Al−17Si−(1,1.5)Fe alloys

The effects of high pressure rheo-squeeze casting (HPRC) on the Fe-rich phases (FRPs) and mechanical properties of Al−17Si−(1,1.5)Fe alloys were investigated. The alloy melts were first treated by ultrasonic vibration (UV) and then formed by high-pressure squeeze casting (HPSC). The FRPs in the as-cast HPSC Al−17Si−1Fe alloys only contained a long, needle-shaped β-Al5FeSi phase at 0 MPa. In addition to the β-Al5FeSi phase, the HPSC Al−17Si−1.5Fe alloy also contained the plate-shaped δ-Al4FeSi2 phase. A fine, block-shaped δ-Al4FeSi2 phase was formed in the Al−17Si−1Fe alloy treated by UV. The size of FRPs decreased with increasing pressure. After UV treatment, solidification under pressure led to further refinement of the FRPs. Considering alloy samples of the same composition, the ultimate tensile strength (UTS) of the HPRC samples was higher than that of the HPSC samples, and the UTS increased with increasing pressure. The UTS of the Al−17Si−1Fe alloy formed by HPSC exceeded that of the Al−17Si−1.5Fe alloy formed in the same manner under the same pressure. Conversely, the UTS of the Al−17Si−1Fe alloy formed by HPRC decreased to a value lower than that of the Al−17Si−1.5Fe alloy formed in the same manner.