TRIBOLOGICAL BEHAVIOR OF A319- Al_2O_3 OR C PARTICULATE COMPOSITES FABRICATED BY STIR AND SQUEEZE CASTING METHODS

摘要

The wear behavior of aluminum alloys has received substantial attention. In dry sliding, ductile materials such as aluminum alloys usually experience severe wear [1-5], which involves substantial surface plastic deformation at the surface. Metal-matrix composites (MMCs) have been received substantial attention from the aerospace and automotive industries because of their improved strength, high elastic modulus and increased wear resistance over conventional monolithic base alloys during the last decade. Improvements in mechanical properties and wear resistance of MMCs have already been demonstrated for a variety of reinforcements [6-14]. A319 alloy is used in transportation vehicle components in which tribological properties are important. It is well known that the wear resistance of Al-Si alloys is influenced by factors such as load and speed as well as microstructural parameters such as the morphology and volume faction of the silicon phase [15-19].A significant improvement in the adhesive wear resistance of Al-Si alloys reinforced with 5 wt. % Al_2O_3 particles was reported by Surappa et al. [20]. Similarly, Pramila et al. [21] noted a decrease in wear rate with increasing of SiC particle content from 15 to 20 wt.% in Al-Si alloy using a pin-on-disc apparatus[6,7]. Generally, it was found that the wear resistance of the composites was considerably higher than that of the aluminum alloy and increased with increasing Al_2O_3 particulates content and size. The majority of the wear behavior of aluminum studies has been undertaken using ferrous counterfaces. It is well known that there are strong adhesive interactions between the aluminum and ferrous materials, as shown by the substantial mechanically mixed layer that is developed in the surface of the aluminum alloy [11,12]. The effect of 2 wt. % graphite particulate addition into Al alloy on the wear rate has been studied by Gibson et al. [22]. They have found that the wear rate of the composite material is significantly reduced by the addition of 2 wt.% graphit particulates. However, with increasing the amount of graphite content to 8 wt.%, the wear rate increases due to the low strength at the interface between graphite particulates and Al alloy. Also, because of the presence of porosity at the interface, the graphite particulates easily fracture and spall along the sliding direction with voids left on the friction surface [23-25]. It was observed that the tribological behavior of the composites in the T6 heat-treated condition is better than in the annealed condition or the unreinforced alloy. Also, it was found that AA6061-SiC MMCs showed a significant improvement in wear resistance over monolithic AA6061 alloy [26-28]. In the present study, the effect of additions of different contents of Al_2O_3 or C particulates into A319 alloy prepared by squeeze casting on the wear and friction behavior under different loads was investigated.