Abstract
A method for equal-channel angular pressing (ECAP) that uses a rotary die was applied to SiC whisker reinforced 7075 alloy composites to produce a fine-grained microstructure suitable to attain superplasticity in the composites. Despite the low ductility of the composites, the rotary die permitted up to 10 passes of ECAP.
The maximum stress during ECAP decreased with increasing the number of passes, and finally became constant at and beyond 4-8 passes. Optical microscopy indicated that the whisker distribution was sufficiently uniform after 10 passes. Transmission electron microscopy (TEM) revealed that the matrix grain sizes were as fine as 1.5-2 μm after 10 passes at 573 K. This composite exhibited high strain-rate superplasticity with elongations reaching 165% over strain rates between 6×10−2 to 6×10−1 s−1. The strain rate sensitivity coefficient (m-value) at these strain rates was estimated to be 0.67.
