Age-Hardening Behavior Of Al-Cu-Sicp Composites Synthesized By Casting Route

Age hardenin,g behaviour of discontinuously reinforced aluminium matrix composites has been a subject of great interest both from scientific and technological view points. The nature of change in kinetics and magnitude of hardening during aging of these composites depend on (a) matrix material(l,2], (b) type of reinforcement including its size, shape and volume fraction[2-41, ( c ) method of processing the composite[2],(d) post fabricati’on treatment [5,6] and (e) temperature of aging[l,2]. In the case of Al-Mg-Si alloy ( 6xxx scriea) based composites, it hna IWCII conclllsivdy sl~owtl that thr prcscnrc of cc*rnlnic rc.illforcc?lrlc.111,~ .SIICII as SiC/Al,& (whiskers, pdiclcs or short fibers ) Icd to accclcrntim in the aging kiuctics whw compared with the unreinforced alloy [4-61. However, in contrast, different results have been reported in the case of hardening behaviour of ceramic reinforced Al-Cu alloy composites. Suresh et al.[3] reported rapid hardening of Al-3.5 Cu-Sic, composites during aging at 190°C compared to the unreinforced alloy. On the contrary, Kim et a1.[7] reported significant retardation in the kinetics of hardening (i.e. increased time to reach peak hardness) during aging of Al-4Cu-SiC whisker composites. However, Harris et a1.[2], h ave shown that Sic, additions have no influence on room temperature aging kinetics of Al-4Cu-Sic, composites compared to the unreinforced alloy. Furthermore, they also report that in case of high temperature aging (aged at 135”C, 17O”C, and 19O”C), composites attain peak hardness much earlier compared to the unreinforced alloy. In the light of the above inconsistencies in these previous investigations, the present work is aimed at understanding the aging bebaviollr of AI-3.2Cu-Sic, composites synthesized by casting route