Ring-core integral method to measurement residual stress distribution of Al-7075 alloy processed by cyclic close die forging

Abstract

Cyclic close die forging (CCDF) is one the severe plastic deformation (SPD) process. In this study, the CCDF has been used to improve the mechanical properties of the Al 7075 alloy. It is observed that performing the CCDF at ambient temperature, cause to catastrophic cracks and breaks. To avoid the breaks, the T6 pick aged samples have been over-aged at 470 °C for 1 h and CCDF has been performed at 200 °C. The mechanical properties of an over-aged Al 7075 alloy processed by CCDF have been examined by tensile test and microhardness. The results have been indicated that performing the CCDF at 200 °C could improve the yield point, ultimate stress and elongation simultaneously. The residual stress distribution after 3, 9 and 15 passes of CCDF has been measured by the ring-core method and integral computational technique. The results indicate that, increasing the CCDF passes at 200 °C decrease the magnitude of the residual stresses in processed Al 7075 alloy. By considering the difference between the principal residual stresses, it is concluded that the diameter of the related Mohr circle is small and consequently trivial shear stress is expected after CCDF process of Al 7075 alloy at 200 °C.