溶湯撹はん法で作製したＳｉＣｐ／７０７５アルミニウム合金複合材料の高速超塑性

Abstract

A SiCp/7075 aluminum alloy composite has been fabricated by a vortex method followed by squeeze casting, extrusion and rolling. The composites were hot rolled to the total rolling reduction of about 94% at temperatures between 573 K to 773 K and at a rolling strain per pass of 0.10. Superplastic characteristics such as microstructure and apparent activation energy were compared with these of the composites made by other processes in order to clarify the superplastic deformation mechanism. Fine grain size of about 1 μm was attained in the composite rolled at a temperature of 573 K and at the strain per pass of 0.1. In the case of rolling at 573 K, the composite obtained exhibited high strain rate superplasticity with a maximum elongation of about 230% at strain rate of 7 × 10−1 s−1 and at 798 K. Plots between e1/n and σ showed linear relation when exponent of n=2 was assumed. Threshold stress obtained from the linear relations were largely dependent on the testing temperature. Apparent activation energy determined from relationship between strain rate and testing temperatures was 244 kJ/mol, which was smaller than that for the powder metallurgical and mechanically alloyed aluminum composites. It seems that there is no substantial difference of high strain rate superplastic mechanism between the composite fabricated by a vortex method and powder metallurgical aluminum alloy composites.