Hot formability of an A12009/20SiCw composite sheet

Although high-strain-rate superplasticity of metal-matrix composites (MMCs) has attracted much research attention in the last decade, most researchers still use uni-axial tensile tests to investigate the formability of MMCs. In this paper, a new fully-computer-controlled superplastic bulge tester has been developed to study the hot formability of an aluminum-matrix composite sheet under complex stress states. Thin 20 vol.% SiC whisker-reinforced 2009 aluminum sheets (2009Al/20SiC(w)) with thicknesses of 2.0 and 2.3 mm were bulged at a constant polar strain-rate of 2.0 x 10(-1) s(-1) and at a optimum temperature of 808 K in elliptical dies with aspect ratios of 1:1, 4:3, 2:1. 8:3 and 4:1. The forming-limit diagram of the MMC was determined for the first time. It was shown that the forming limits increases with increasing sheet thickness, and that the general shape of the curve is different from that of conventional forming-limit curves. (C) 1998 Elsevier Science S.A.