Microstructural Development in AL-LI-CU-MG Alloys and Metal Matrix Composites
Author | : |
Publisher | : |
Total Pages | : 204 |
Release | : 1995 |
ISBN-10 | : OCLC:227846349 |
ISBN-13 | : |
Rating | : 4/5 (49 Downloads) |
Book excerpt: The aging responses of both an 8090 alloy and a SiC reinforced 8090 alloy matrix composite, at 190 deg 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 delta' phase (Al3Li) and the S' phase (Al2CuMg) 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 delta' phase was not affected by the high density of dislocations in the composite, acceleration of the S' precipitation was indicated by DSC. The dislocation distribution in the composite was quantitatively compared with that in the unreinforced 8090 alloy. The addition of SiC to the 8090 alloy caused a highly non-uniform dislocation distribution in the composite. This non-uniform dislocation distribution is directly responsible for the unchanged aging response in the composite as indicated by microhardness tests.