In this research, the in situ Si and Fe-rich particles reinforced Al matrix composites were fabricated by rheocasting(RC) process assisted with ultrasonic vibration(USV). After USV treatment, the polygonal primary Si crystals were refined into particles with average diameter of about 15–23 lm, and the fraction of primary Si declined to about5.4–6.5 vol%. The coarse plate-like d-Al4(Fe,Mn)Si2phase was transformed into fine particles with average diameter of about 17–20 lm, and the fraction of particle-like Fe-bearing particles is about 3.6–5.3 vol%. The ultimate tensile strength of the RC composites increases with the increase of Fe content at 350 °C. The increase of the elevated temperature strength of the composites is mainly attributed to the refinement of d-Al4(Fe,Mn)Si2phase and the increase of the volume fraction of the Fe-bearing compounds. Compared with the composites without USV, the RC composites assisted with USV have thinner mechanical mixing layer in wear test, which corresponds to smaller wear rate.
15 vol% silicon carbide particle(Si Cp)-reinforced 2009 Al matrix(15 vol% Si Cp/2009Al) composites were fabricated by hot isostatic pressing(HIP) and hot extrusion processes. The tensile and fracture properties of 15 vol% Si Cp/2009 Al were studied. The results showed that hot extrusion increased the ultimate tensile strength(UTS), yield strength(YS), elongation(EL), reduction in area(RA), and fracture toughness of the composites. The heat treatment resulted in the increase in UTS, YS, and fracture toughness, but a decrease in EL and RA. Both hot extrusion and heat treatment had negligible effects on elastic modulus(E). With the increase of Si Cpsize, the UTS, YS, and E decreased, but the EL and RA increased. The fracture toughness increased first and then decreased with increasing Si Cpsize, and when the Si Cpsize was about 7 lm, the composites obtained the maximum fracture toughness value of 31.74 MPa m^(1/2).
Carbon nanotube-reinforced 2009Al(CNT/2009Al) composites with randomly oriented CNTs and aligned CNTs were fabricated by friction stir processing(FSP) and FSP-rolling, respectively. The CNT/2009 Al composites with aligned CNTs showed much better tensile properties at room temperature and elevated temperature compared with those with the randomly oriented CNTs, which is mainly attributed to larger equivalent aspect ratio of the CNTs and avoidance of preferential fracture problems. However, much finer grain size was not beneficial to obtaining high strength above473 K. The aligned CNTs resulted in tensile anisotropy, with the best tensile properties being achieved along the direction of CNT aligning. As the off-axis angle increased, the tensile properties were reduced due to the weakening of the load transfer ability. Furthermore, aligned CNTs resulted in much lower coefficient of thermal expansion compared with randomly oriented CNTs.
