The Friction And Wear Properties Of Si/Al And B₄C/6061A1Composites

Abstract:Aluminum-matrix composites have attracted attention due to their low thermal expansion coefficient, high wear resistance and ease of fabrication. Si, B4C have lower densities than SiC and Al2O3, they not only satisfy the requirements in light weight of aluminum matrix composites but also improve their specific modulus, strength and wear resistance.We take Si/Al and B4C/6061Al as the research subjects which fabricated by powder metallurgy and stir casting, respectively. Scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), transmission electron microscopy (TEM) and brinell hardness et al. were used to investigate their microstructures and properties. UMT-3friction testing machine and microscratch testing machine were used to characrerize the influence of Si content, hot-pressing temperature on the friction and wear properties of Si/Al composites and the influence of sliding times, loads, sliding velocities and heat treatments on the friction and wear properties of B4C/6061Al composites. The results show that:1)The microstructure of the composites contain Al-rich region, Si-rich region and Al-Si mixed region. The relative density decrease with the rise of Si content. Al-40Si has the highest hardness, lowest mass loss and friction coefficient with abrasive wear and oxidation wear as its main wear mechanism.2) The relative density and the brinell hardness increase with the rise of hot-pressing temperature, while the mass loss and friction coefficient decrease. So the composite hot-pressed at550℃has the highest wear resistance and the best antifriction.3) The wear process of the composites experience running-in wear, stability wear and severe wear with the rise of sliding time. The mass loss and friction coefficient also increase. The severe wear happens after120min with delamination wear and adhesive wear as its main wear mechanism. With the increase of the load, the mass loss also increase. The composite experiences severe wear at the load of30N with the highest average value and fluctuation of friction coefficient. Delamination wear and abrasive wear are its main wear mechanism. The mass loss, friction coefficient and its fluctuation rise at first, then decline with the sliding velocity. The fretting wear happens when the sliding velocity reaches240r/min which is coursed by severe adhesive phenomenon. After that, the wear experiences a steady process with abrasive wear and delamination wear as its main wear mechanism.4) After aged at180℃for15h, needle-sized β" phases precipitate from Al matrix and the hardness of B4C/6061A1composite reaches a peak value. It shows the shallowest scratch deepth and lowest friction coefficient along with its fluctuation. With the rise of the loads, both scratch deepth and friction coefficient increase with more severe adhesive wear happens.