Effect of Modification of the Microstructure of a Cast Al-33%Cu Eutectic Alloy by Isothermal Heat Treatment in the Semisolid State on its Adhesive Wear Characteristics

摘要

The adhesive wear characteristics of an as-cast eutectic Al-33%Cu alloy having a typical lamellar structure have been compared with that of the same alloy having a modified microstructure by the block-on-wedge wear test. The modification of the as-cast microstructure was effected by isothermal heat treatment in the semisolid state (SSH) at 560°C for 10 min followed by water quenching. The modified microstructure consisted of globules of hypereutectic β copper aluminides globules dispersed in the α-Al matrix. During the wear test, the counter body was a EN31 steel drum of hardness Rc62. Cumulative wear loss and coefficient of friction decreased after modification of the cast structure by SSH. FESEM examination of the worn surfaces and wear debris revealed that oxidative wear was more prominent in case of the sample with the modified microstructure. However, removal of the oxide nodules, plastic deformation of the matrix, micro-cracking and delamination of the matrix accounted for the wear loss in both the cases. Conspicuous pick-up of iron, presumably by diffusion from the drum into the debris of oxide nodules, was noted in case of the cast sample. Iron pick-up was much less in the debris of the modified sample.