SUPERPLASTICITY IN DOUBLY EXTRUDED MAGNESIUM COMPOSITE ZK60 SIC/17P/

Superplasticity in a doubly extruded magnesium based composite, ZK60 r einforced with 17 vol-%SiC particles, was investigated. The influences of strain rate on the flow stress and elongation in the composite wer e characterised. It was found that the composite exhibited superplasti city (elongation > 400%) at high strain sates (similar to 0.1 s(-1)). In addition, the material showed a high strain rate sensitivity of 0.5 and an activation energy of 81 kJ mol(-1) in the superplastic region. Based upon these results, it was proposed that the dominant deformati on mechanism is gain boundary sliding accommodated by a grain boundary diffusion process. A comparison of the superplastic behaviour was als o made between the doubly extruded and singly extruded composites. (C) 1998 The Institute of Materials.