MICROSTRUCTURAL DEVELOPMENT IN AL-LI-CU-MG ALLOYS AND METAL MATRIX COMPOSITES

Professor in Charge of Metals Science and Engineering Option The aging responses of both an 8090 alloy and a SiC reinforced 8090 alloy matrix composite, at 190*C, have been fully characterized for the first time using various analytical techniques. Two stage hardening was observed in both materials and somewhat unexpectedly, the aging response of the composite was unchanged as compared to the unreinforced 8090 alloy. Microstructural development during the aging of both materials was studied using electron microscopy and differential scanning calorimetry (DSC). Transmission electron microscopy (TEM) examination indicated that the 8' phase (Al3Li) and the S ' phase (A12CuMg) were the two principal strengthening phases in both materials. These two phases formed at different stages during aging and caused the two stage strengthening. Although the precipitation of the 8 ' phase was not affected by the high density of dislocations in the composite, acceleration of the S ' precipitation wa