Spray forming of Al–Si–Pb alloys and their wear characteristics

A modified spray forming process is described to synthesize liquid immiscible alloys based on Al–Si–Pb system. The atomization of the melt was carried out at a gas pressure of 1.0 MPa and the nozzle to substrate distance was varied from 0.35 to 0.55 m. The microstructure and wear characteristics of the spray-deposits were investigated. The results invariably exhibited an equiaxed grain morphology of the primary α-phase with variation in grain size from 10 to 25 μm in addition to a uniform dispersion of ultra-fine particles of lead and globular silicon particles in Al-matrix. The size of Si particles varied from 0.5 to 5 μm and that of Pb particles from 0.1 to 25 μm with variation in deposition distance. The microstructural variation was also observed in different regions of the deposit. The atomized powder particles revealed two different types of microstructures, the one showing a cellular-dendritic morphology of the primary α-phase whereas the other exhibited fine spherical Al-particles dispersed in the matrix of Pb-rich phase. The wear rate and the coefficient of friction of Al–Si–Pb alloy were observed to be lower than that of Al–Si alloy at loads varying from 10 to 90 N at a sliding velocity of 1.0 ms−1. The possible reasons for this behaviour are discussed in the light of microstructural features of the alloy and the nature of the worn out surfaces of the wear test specimens.