Dry Sliding Friction and Wear Behaviour of an Electron Beam Melted Hypereutectic Al–Si Alloy

The economic and environmental benefits of using light-weighting technology in automotive applications continue to attract attention for feasible commercial solutions. This study investigates the use of pulsed electron beam melting of a hypereutectic Al–Si alloy as a possible modification procedure for cylinder crankcase bore facing surfaces. Machined surfaces of an A390 alloy were subjected to five pulsed electron doses with an applied cathode potential between 16.5 and 36 kV. It was found that increasing beam accelerating voltages led to an initial decrease (1.4 μm Ra) but subsequent increase (4.0 μm Ra) in average surface roughness values associated with surface crater formation due to sub-surface melting and eruption. Surfaces were tested under dry sliding tribological conditions against 52100 bearing steel in a reciprocating geometry. Average dynamic friction coefficients were higher (0.9) compared to the untreated alloy surface (0.6) as a result of a greater degree of adhesion to the counterface. However, FIB cross sections of worn surfaces indicated that this activated an oxidative type wear process which ultimately led to the formation of a beneficial surface tribo-film on the EBM-treated surfaces, improving the specific wear rates by up to 66%.