Recrystallization Kinetics of Cold-rolled Squeeze-cast Al/SiC/15w Composites

Abstract

Al-SiCw composites can be readily shaped with conventional secondary metalworking techniques. During such forming operations, Al-SiCw composites may experience appreciable amounts of cold work, which may both influence their further forming operations and degrade some mechanical properties. Therefore, after forming operations it may be necessary to anneal the composites. Mostly, recrystallization annealing is used to achieve this purpose. The purpose of this study is to give useful information on thermomechanical processing of Al-SiCw composites by investigating their recrystallization kinetics. Al/SiC/15w composites are fabricated through a squeeze casting route followed by a hot extrusion at an extrusion ratio of 18: 1, and cold-rolled to 30, 50, and 70% of the original thickness, respectively. Then as-cold-rolled Al/SiC/15w composites are heated either continuously or isothermally to make the composites recrystallize. To investigate the kinetics of the cold-rolled composites during heating, differential thermal analysis (DTA) and hardness testing are carried out. It is found that the recrystallization kinetics of Al/SiC/15w composites is strongly dependent on deformation degree. When the reduction in thickness is less than 50%, with the increase in reduction in thickness, a faster kinetics of recovery and recrystallization occur. When the reduction in thickness is more than 50%, however, with the increase in reduction in thickness, only a faster kinetics of recovery occurs and the kinetics of recrystallization is nearly not influenced. Whiskers play a role in promoting the kinetics of recrystallization by particle-stimulated nucleation (PSN). While solute atoms make the kinetics of recrystallization largely delayed, precipitates only slightly slow down the recrystallization kinetics. At 280°C, between 100 and 200 s, extended recovery reaction and recrystallization nucleation are dominant. After 200 s, however, the growth of recrystallized grains becomes a dominant softening mechanism. As a result of the recrystallization taking place before aging, aging kinetics of the cold-rolled solution-treated 6061Al-SiCw composite is delayed.