Preliminary Study on Mechanical Response and Microstructural Evolution of Al-Cr Alloy under Varying Heat treatment Conditions


  • Ajide O. O., Anonyuo K. I., Akande I.G., Ajao O. J.


High performance materials are known to enhance the economy of production due to their ability to withstand desired engineering applications. In view of this, Al-Cr alloy with varying amounts of chromium was developed using two-step stir-casting method.The suitable volume fraction for various Al alloy and Cr combination were 99.5Al-0.5Cr, 99Al-1Cr, 97Al-3Cr and 94Al-6Cr. 99.5Al-0.5Cr alloy which relatively best mechanical properties was selected and subjected to solution heat treatment at 450? for 20 minutes and also aged at various temperatures (120, 130, 150, 160 and 170 ?) for 45 minutes. The mechanical response (ultimate tensile strength, hardness and impact) of the as cast (un heat treated) alloys were investigated. The ultimate tensile strength (UTS), hardness and microstructure of the artificially aged 99.5Al-0.5Cr alloy were further investigated. The microstructure of 99.5Al-0.5Cr alloy was examined using Optical Microscope (OPM). Among the as cast alloys, the 99.5Al-0.5Cr alloy exhibited the highest UTS and hardness values of 106.93MPa and 58.3 Kgf/mm2, respectively. Maximum UTS and hardness values of 123.46 MPa and 89.7 Kgf/mm2 , respectively were obtained for 99.5Al-0.5Cr alloy at 160 ? of artificial aging, which showed that the aging effect increased the UTS, hardness and impact strength values of 99.5Al-0.5Cr alloy by15.63 , 53.90 , and 39.39%, respectively. The 99.5Al-0.5Cr alloy artificially aged at 160 ?exhibited the highest impact strength value of 22.44 J/mm2 among other samples. The agehardening noticed in 99.5Al-Cr0.5alloy was ascribed to the hardening effect of heat and precipitation ofintermetallic chromium as revealed bythe OPM micrograph. The outcome of this study has shown that chromium alloying element has potentials for improving mechanical properties and the benefits of aged hardening effect on Al-Cralloy can be explored for various industrial applications.