FRICTION AND WEAR BEHAVIOR OF CAST AND SINTERED AL-SI ALLOYS UNDER CONDITIONS OF OSCILLATING CONTACT

Three aluminium-silicon alloys were characterized with respect to their wear behaviour under conditions of oscillatory relative motion in contact with cast iron in an environment of kerosene, applying initial line contact, forces of 37, 74 and 129 N, a frequency of 33 s-1 and amplitudes in the range 117-459-mu-m. The initial (hertzian) contact pressures P(Hi) amounted to 53, 75 and 98 MPa, and the pressures P(c) at full conformity were 1.5, 3.0 and 5.4 MPa respectively. The tests were supposed to simulate, at least to a first approximation, piston ring-piston ring groove contact. The alloys were a conventional cast A-390 alloy and two alloys produced and processed by the powder metallurgy (PM) route ("PM alloys"). It is found that the initial wear rates of the PM alloys are much lower than those of the cast material. This effect is particularly pronounced at the lower value of the initial (hertzian) contact pressure of 53 MPa. However, on running-in (attainment of full conformity between stationary and moving specimens), the three alloys eventually acquire practically the same specific wear rate, i.e. (0.11-0.15) x 10(-6) mm3 N-1 m-1 at P(Hi) = 53 MPa and 1.2 x 10(-6) mm3 N-1 m-1 at P(Hi) = 75 MPa. These observations are explained in terms of (changes in) microstructure and wear mechanism.