Age-hardening characteristics of Al{sub}2O{sub}3 continuous fiber reinforced Al-Si-Cu alloys

摘要

The age-hardening process of Al{sub}2O{sub}3 continuous fiber reinforced Al-Si-Cu and Al-Si-Cu-Mg alloys was investigated by using a TEM, DSC, Vickers macro hardness tester and EPMA. A series of composite specimens were solution treated at 773 Kfor 10 h, and subsequently aged at 433 K and 473 K for 10 min to 10{sup}4 min. The aging characteristics of the composites were compared with those of the unreinforced alloys which were cast and heat treated under identical conditions as the composites.Although the precipitation of composites is accelerated, the overall age-hardening sequence is similar to that of unreinforced alloys. In the case of Al{sub}2O{sub}3/Al-Si-Cu alloy composite, the degree of age-hardening (ΔHV = HV. Max-HV. s) is higherthan that of unreinforced alloy, because the θ' phase precipitated preferentially on the dislocations is more uniformly dispersed in the composite with higher density of dislocations. On the contrary, in the Al{sub}2O{sub}3/Al-Si-Cu-Mg alloy composite,the λ' phase homogeneously precipitates in the α matrix independent of dislocations. However, the precipitation amount of λ'phase is decreased due to the prior formation of MgAl{sub}2O{sub}4 (spinel) at the interface between the Al{sub}2O{sub}3 fiberand matrix alloy. Therefore, the precipitation rate is almost unchanged and the degree of age-hardening is slightly decreased by the presence of Al{sub}2O{sub}3 fiber.