DRY SLIDING WEAR AND CORROSION BEHAVIOR OF AA7075-SiC COMPOSITES

Automobile structural components are subject to high stress, friction and corrosive environmental conditions. Though aluminum alloys exhibit lightweight and high corrosion resistance, there is a need to improve the high strength-to-weight ratio and resistance to friction. This paper presents microstructural analysis, hardness, dry sliding wear behavior, and corrosion behavior of AA7075 reinforced with silicon carbide (SiC) particles. The composite specimens were prepared at the concentration of 2.5 and 5wt.% SiC. The microstructure of AA7075 showed dendritic morphology while composite specimens showed nondendritic morphology grains. Reinforcement of SiC resulted in increased nucleation site and refinement of grain during solidification. XRD analysis of base alloy showed alpha matrix with eta (MgZn2), T(Al-Zn-Mg-Cu) and Al7Cu2Fe phases, while the composite sample showed the presence of additional S(Al2CuMg) and theta (Al2Cu) phases. Composite samples showed higher hardness values than base alloy due to grain boundary strengthening and Orowan strengthening. The enhancement of hardness of AA7075 by 20% and 37.5% were obtained with the addition of 2.5 and 5wt.% SiC particles respectively and also predicted with less coefficient of friction and less wear rate at all the tested load conditions. At the same time, the respective reduction in wear rates of AA7075 was found to be 50 and 65%. The worn-out surface of the base alloy was found to have undergone extensive plastic deformation and resulted in delamination with extensive patches and no clear groove marks. The composite sample of 2.5wt.% SiC showed mild patches with clear groove marks, while the Composite of 5wt.% SiC showed groove marks with fine width parallel to sliding directions. The wear mechanism was found to be transferred from adhesive mode to abrasive mode through a mixed mechanical layer with an added concentration of SiC particles from 0wt.% to 5wt.%. Weight loss during immersion corrosion increases with an increase in the amount of SiC due to an increased amount of metallic phase which increases microgalvanic corrosion and pitting. Hence, composite samples showed decreased corrosion resistance than base alloy.