Characteristics of tribolayers observed in A356 Al alloy - SiC_P composite discs/brake pad during sliding wear tests

Tribological characteristics of A356 Al alloy-10 vol. % SiC_p composite discs/brake pad has been studied under dry sliding conditions at sliding speeds in the range 2 to 5 m/s and at loads in the range 1-3 MPa. In these tests, disc of Al MMCs and pin of friction pad made of polymer based composite were used. Wear rates of Al MMC disc as calculated by weight loss method, found to be negative at high sliding speed and high load. Worn surface of disc has been analyzed using EDAX. SEM analyses of worn surfaces of composite disc infer transfer of material from pin to the disc resulting in the formation of tribolayers. Two types of tribolayers were observed on the worn surface, one having shiny appearance of copper rich layer and other is dark in colour consisting of Mg, S, Fe, Ba, Ca, Si, Cu, In and Al. In the later layers were rich in copper and appear as bright patchy layers under SEM. Coverage of copper rich layers increase all along and across the worn track at a sliding speed of 4 and 5 m/s in the load range 2 to 3 MPa. Atomic percent of copper increase with load and consequently affect the wear rate of disc. EDAX analysis of dark tribo layers on wear track of composite disc show continuous increase in the amount of Cu and Ba with increase in speed and load. Hence, wear rate of composite discs were relatively low under all test conditions. These results clearly indicate composition of friction material having profound influence on the wear rate of Al MMC discs.