Investigation of equal-channel angular pressing of steel/copper bimetallic rods and effect of Cu-shell thickness on imposed surface stretch

To determination of equal-channel angular pressing(ECAP) process on the stress-strain behavior of  steel core of steel/copper bimetal and also effect of Cu-shell thickness on the created surface stretch during ECAP, the bimetallic samples composed of steel rods with 8 mm diameter and copper shells with 0.75 mm thickness are prepared. The both bimetallic samples and steel rods with 9.5 mm are subjected to consecutive ECAP process using die with inner angle 90o and an outer curvature corner angle of 30o. The applied load and punch displacement are recorded during samples passing through an ECAP die. The tensile testing is carried out on both the initial and ECAPed series. Moreover, dependence of surface stretch to diameters, shell thickness and strength properties of constituents of core/shell bimetallic rods is analytically modeled. Then, the finite element method(FEM) is used to investigate the effect of Cu-shell thickness. The obtained results revealed that the ultimate tensile strength of bimetallic core and steel rods are improved approximately 60% and 108% by ECAP deformation, respectively. The applied punch load for passing of bimetallic sample through an ECAP die is 54% less than the ones for steel rod. According to the FEM results, the maximum value of surface stretch is linearly decreased with increasing the thickness of copper shell. The obtained results show a good agreement between the analytical model and FEM approach.