Constrained Constant Radius Pressing (CCRP) process to improve mechanical properties and microstructural homogeneity of pure copper sheet

Abstract

Constrained groove pressing (CGP) is a well-known severe plastic deformation (SPD) process used to improve the mechanical properties of metallic sheets by forming the ultrafine grain (UFG) structure. The conventional CGP process employs 45° grooved dies to impart good amount of plastic strain on the specimen without altering the specimen's initial dimensions. The literature indicates that conventional CGP-processed sheets have inherent strain inhomogeneity. In the present investigation, an effort was made to minimize the inherent strain inhomogeneity by modifying conventional CGP dies into symmetric constrained constant radius pressing (CCRP) dies. Three distinct CCRP dies with varying radius of curvature and die parameters were designed to attain the optimal combination of mechanical properties. It was found that metal sheets processed by new modified dies (CCRP) exhibit improved ductility and significantly enhanced toughness, in contrast to the sheets processed by conventional CGP dies. The improvement in mechanical properties could be attributed primarily to homogeneous grain refinement. In addition, the finite element analysis (FEA) was used to simulate the influence of different die designs on the strain distribution across the sheet, and it showed that lower die angle of CCRP lead to more homogeneous distribution of strain across the arc of the CCRP die.