WORK-HARDENING BEHAVIOR AT THE WORN SURFACE OF AL-CU AND AL-SI ALLOYS

In order to predict the ability of a material to support the load appl ied at asperities, the flow stress of the surface regions must be know n. However, there is little quantitative data on the work hardening be haviour resulting from plastic sliding contact. Both linear hardening and the achievement of a saturation flow stress have been predicted. T wo binary Al alloys, Al-4wt.%Cu and Al-11.7wt.% Si, were worn against a cast iron disc in a tri-pin-on-disc machine, under dry sliding condi tions at 1 m s(-1) over the load range 6-40 N. Detailed transmission e lectron microscopy was performed on cross-sections taken from worn sur faces of both materials. The subgrain size was found to decrease subst antially as the surface was approached for both alloys. In the Al-Si a lloy, the Si particle size was also found to decrease as the surface w as approached. Taper sections were taken parallel to the sliding direc tion and the microhardness was measured as a function of depth below t he worn surface. The equivalent strain was measured from the displacem ent of prominent microstructural features such as grain boundaries. Th is allowed stress-strain curves to be constructed for the worn surface of the two materials. The stress-strain data were interpreted in rela tion to established work hardening laws, and correlated with the subgr ain size. The maximum flow stress observed correlated with a minimum s ubgrain width of approximately 0.2 mu m in the Al-Cu and approximately 0.4 mu m in the Al-Si alloy. (C) 1997 Elsevier Science S.A.