Dry wear characteristics of machined ZL109 aluminum-silicon alloy surface under unidirectional and reciprocating rolling-contact friction

Dry wear characteristics of machined ZL109 piston aluminum-silicon alloy surface were investigated in this paper. The wear characteristics of unidirectional friction is also analyzed to reveal its reciprocating wear characteristics better. The wear rates, wear debris and surface morphology versus wear time, and the causes of friction squeal under unidirectional and reciprocating rolling-contact were studied in detail. The surface topography, surface phase, surface roughness and residual stress of ZL109 aluminum-silicon alloy machined surface before and after wear were measured. The results indicate that the wear rates fluctuates with the wear time increasing under unidirectional rolling-contact, however, the wear rates first decreases and then stabilizes at about 1.5 mg min(-1) with reciprocating wear. The wear rate under reciprocating wear is obviously higher than that of unidirectional wear, which is mainly affected by the reciprocating stress, new phase production and its content in the wear surface. There is no friction noise during reciprocating rolling-contact, however, and the fluctuation of high-hardness corundum content could lead to the friction squeal in unidirectional wear. There are flake and granular wear debris mainly, and the granular debris is mainly produced by extruding the flake debris repeatedly. There is high-degree surface plastic deformation during reciprocating wear versus that of unidirectional wear. The maximum surface residual compressive stress of reciprocating wear is higher than that of unidirectional wear, which is accounts for 62.9% of ZL109 aluminum-silicon alloy's yield limit. Fatigue wear is main mechanism of machined ZL109 aluminum-silicon alloy surface. Fatigue wear and delamination wear are all essentially the surface material failure phenomena caused by the expansion of micro-cracks and micro-holes in the sub-surface layer.