The use of response surface methodology in cryrolling of ultrafine grained Al6061 to improve the mechanical properties

Abstract

In this paper, mechanical properties of Al6061 alloy sheets severely deformed by the cryorolling process are investigated using response surface methodology. Four control parameters including the total thickness reduction, aging temperature, aging time, and short annealing temperature are selected as the influencing parameters. The influence of these parameters on the mechanical behavior of processed samples is studied through the measurement of yield strength, ultimate tensile strength, ductility, and hardness. Analysis of variance showed that the experimental and predicted values are in good agreement and the response surface methodology could be effectively applied in the cryorolling processing for finding an economical and optimum condition to achieve simultaneous improvement in the strength and the ductility of Al6061 alloy. After short annealing of the cryorolling specimens (with 90% total thickness reduction) at 205℃ for 5 min followed by aging at 148℃ for 39 h, the yield strength, the ultimate tensile strength, and the hardness, increased by 24%, 20%, and 40% respectively compared with unprocessed Al6061 alloy and the ductility of 12% was obtained. The results of X-ray diffraction analysis confirm the evolution of precipitates which are consistent with the measured hardness and tensile properties. Also, fractography analyses of fracture surfaces for bulk Al6061, cryorolled and post aging tensile specimens are performed using scanning electron microscopic images.