AGE-HARDENING BEHAVIOR OF AL-CU AND AL-CU -MG BASE COMPOSITES REINFORCED WITH SIC WHISKER

Precipitation sequences of the age hardenable aluminum alloy composite s are strongly affected by the dislocations generated during quenching from the solution treatment temperature. In this study, age hardening behavior of Al-4 mass%Cu and Al-4 mass%Cu-1.5 mass%Mg base composites reinforced with SiC whisker (SiCw) was investigated with micro-Vicker s hardness measurement, differential scanning calorimetry and transmis sion electron microscopy. SiCw/Al-Cu and SiCw/Al-Cu-Mg composites indi cate a remarkable age hardening in spite of the suppression of the G.P . zone or G.P.B. zone formation rate, and the age hardening rate is ac celerated. In particular, age hardening of the SiCw/Al-Cu-Mg composite is larger than that of the unreinforced alloy. The precipitation proc ess of the SiCw/Al-Cu composite is different from that of the unreinfo rced alloy. Many metastable theta' phases (Al2Cu) precipitate preferen tially on dislocations in the matrix prior to G.P. zone and contribute for the age hardening of the composite, but the posteriorly formed G. P. zone still plays the most important role in the hardness increase. In the case of the SiCw/Al-Cu-Mg composite, the age hardness steeply i ncreases with the formation of the G.P.B. zone at the initial stage an d decreases temporarily and then increases again due to the precipitat ion of a fine and high dense S' (Al2CuMg) phase.