The effects of processing environments on the microstructure and mechanical properties of the Ti/5083Al composites produced by friction stir processing

The hard metallic particle as reinforcements can improve the strength of Al matrix without severely sacrificing its ductility. However, it is technically challenging to fabricate metallic particle reinforced aluminum matrix composites (AMCs) for easy reactivity of Al with most metals. In the present work, friction stir processing (FSP) was used to disperse titanium particles into 5083 Al matrix to fabricate AMCs. Especially, FSP was performed in water to better inhibit the Al/Ti interfacial reaction and the recrystallized grain growth. The effects of the external water on the microstructure and mechanical properties of FSPed AMCs were investigated. Results showed that the external water significantly lowered peak temperature and increased cooling rate, which not only rapidly reduced material flow, but also effectively inhibited grain growth, thereby creating finer grains about 1 μm. Also, an excellent Al/Ti interfacial bonding consisting of an element solid solution was obtained in both FSPed composites. Tensile test results indicated that water-FSPed AMCs possessed the higher yield strength (265 MPa) and ultimate tensile strength (423 MPa) compared with the 5083Al matrix (YS: 198 MPa, UTS: 301 MPa) and the air-FSPed AMCs (YS: 236 MPa, UTS: 383 MPa). Moreover, an appreciable amount of ductility (14.9%) was retained despite of their evidently increased strength.