Elevated Temperature Properties And Hot Processing Map For Particle Reforcing Magnesium Matrix Composites

At present, due to the world energy crisis and environment pollution has been one of key problem in human development, Magnesium alloys are attracting more and more attention in automobile industry for losing the weight of a vehicle,reducing the exhaust emissions and raising fuel efficiency. However, the poor thermal resistance properties of magnesium alloys restrict development and application of magnesium alloys in automobile industry. Introducing reinforcements in Mg alloys is one of the effective ways to improve the comprehensive performance of Mg alloys. However, the presence of hard ceramic particles in the soft magnesium matrix alloys deteriorates the original poor workability of Mg, which is due to the crystal structure. Therefore, how to choose the appropriate hot deformation technology to improve the hot workability and the microstructure of the magnesium matrix composites is a key issue in the development of excellent magnesium matrix composites. This research is focus on the above problem. The hot workability of TiCp/AZ91D magnesium matrix composites have been researched in two aspects: the hot flow behavior and hot processing map. The main conclusions are as follows:Steady-state flow characteristics were observed during hot deformation of TiCp/AZ91D magnesium matrix composites in cast condition, and the flow stresses decrease with the increasing of temperature and the decreasing of strain rate. The reinforce effects of ceramic particles on the AZ91D alloys has faded away with the increasing of temperature. The main reason is that the formation of TiC particles promoted the dynamic recrystallization processing,and weaken the strengthen effects of dislocation.The hot processing map of 3vol.%TiCp/AZ91D magnesium matrix composites exhibit that there are two dynamic recrystallization regions and two instable regions at the temperature range of 250-400°C and the strain rate range of 10-3-8s-1. The main instable mechanisms are indentified using the microstructure observing. The flow localization was due to localized shear at the range of 250-350oC, 10-0.5-10s-1; the seriously clustered particles, which was due to the inhomogeneous dynamic recrystallization processing, is the main reason for the flow instable at range of 250-300oC, 10-2.5-10-1.5s-1. ?According to the hot processing map of 3vol.%TiCp/AZ91D magnesium matrix composites, the hot extrusion technological parameter were chosen. The extruded TiCp/AZ91D composites samples were got. Based on compression tests at high temperature in extrusion condition, the effect of hot extrusion technological parameter on on the compression properties at high temperature, creep properties at high temperature were investigated. The investigation results show that the extrusion improve their compression properties; the creep resistance of composites has been obviously increased. Meanwhile, the strength effects on high temperature have been improved.