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Vol.29, No.11, 1178 ~ 1186, 1991

Title

High Temperature Fracture mechanism of a 2124 Al - SiCw Composite

노병일Byung Il Roh, 이두영Doo Young Lee

Abstract

To investigate high temperature fracture mechanisms of Al composites, tensile test. were Conducted on a 2124 Al-SiCw composite and a 2124 Al alloy varying the test temperature from 25℃ to 550℃ and the strain rate from 5×10^(-3)s^(-1) to 0.3s^(-1). At test temperatures above 475℃ the tensile strength of the composite became lower than that of a 2124 Al alloy. Also, the strain rate for the maximum elongation to the failure of the Al-SiCw (0.1s^(-1)) is much higher than that of the 2124 Al (5×10^(-3)s^(-1)) at 500℃. These experimental results suggest that the 2124 Al-SiCw can be superplastically formed with a much faster rate at a lower stress level compared with the 2124 Al. Detailed microstructural and fractographic analyses indicate that the major fracture mechanism of the 2124 Al-SiCw shifts from void initiation and coalescence to cavity formation and growth as the test temperature increases. It is of great interest, to find that the cavity initiation sites of the 2124 Al-SiCcw are strongly influenced by the strain race at high temperatures;whisker-sides at high strain rates and whisker-ends at low strain rates. Furthermore, the favorable cavity growth direction is also Found to be a function of the strain rate; at high strain rates perpendicular and at low strain rates 45° to the tensile axis. The change in the favorable cavity initiation sites and cavity growth direction with the strain rate can be explained by the relative superiority between the matrix/whisker interfacial strength and the matrix shear strength.

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