DYNAMIC DEFORMATION-BEHAVIOR OF AL-ZN-MG-CU ALLOY MATRIX COMPOSITES REINFORCED WITH 20 VOL-PERCENT SIC

The dynamic mechanical response and substructure evolution of underaged and overaged Al-Zn-Mg-Cu alloys with and without 20 vol.% SiC particles were investigated and compared to those following quasi-static compression. The hardening rates of the overaged composites and control alloys were found to be smaller than those of their underaged counterparts. Overaged composites and the control alloys showed more strain rate sensitive behavior than the underaged composites and alloys. The flow stress of the composites was found to decrease at total strains larger than 0.15 in the high-rate Hopkinson pressure bar tests. A more rapid decrease in stress in the underaged composites suggests that microstructural damage in the underaged condition is greater than that in the overaged condition tested at high strain rates. Cracks near the SiC/matrix interfaces were observed more frequently in the underaged Hopkinson pressure bar samples. The more frequent interface cracks in the underaged composites are thought to result from much slower relaxation of the stresses and strains built up at the interface due to much more difficult thermally activated deformation.