ELECTRIC-FIELD MODIFICATION DURING SUPERPLASTIC DEFORMATION OF 15 VOL-PERCENT SICP LY12 AL COMPOSITE/

Silicon carbide particulate-reinforced aluminium (SiCp-Al) composites possess a unique combination of high specific strength, high elastic m odulus, good wear resistance and good thermal stability, which makes t hem attractive as metal matrix composites (MMCs). Some work focusing o n the superplasticity of SiC particulate reinforced composites has bee n conducted in order to improve the formability. The study of superpla stic deformation in the presence of an external electric field is a re latively new development, but to the authors' best knowledge, has not pet been reported for MMCs. In this paper, 15 vol% SiCp/LY12 Al compos ite was fabricated by spray atomization and co-deposition and pre-trea ted by isothermal hot compression as well as isothermal hot forward ex trusion (extrusion ratio: 10.0). The superplastic deformation behaviou r of the 15 vol% SiCp/LY12 Al composite under an external electric fie ld has been investigated. The electroplastic effect of 15 vol% SiCp/LY 12 Al composite and the influence of deformation process parameters on the superplasticity have also been studied. The experimental results show that: (i) the optimum intensity of the electric field improves th e superplasticity of 15 vol% SiCp/LY12 Al composite, i.e. the strain-r ate sensitivity index (m) is increased by 13% and the elongation (delt a) is 420%, being increased by 20%; (ii) the optimum intensity of the electric field decreases the flow stress by 16% during the superplasti c deformation of 15 vol% SiCp/LY12 Al composite; (iii) the optimum int ensity of the electric field makes the grain size finer during the sup erplastic deformation of 15 vol% SiCp/LY12. Al composite, which provid es the microstructural conditions for the improvement of superplastici ty, but the electric field has only a slight influence on the microstr ucture before superplastic deformation. (C) 1998 Elsevier Science S.A.