The formation mechanism, mechanical properties and thermal stability of the pure copper sheet with gradient structure processed by plastic flow machining

Abstract

Plastic flow machining (PFM) is a novel severe plastic deformation (SPD) process. Ultrafine-grained metal sheets or strips with gradient structures are processed by PFM in a single step under the combined effects of cutting and pressing. In this paper, the formation mechanism, mechanical properties, and thermal stability of pure copper sheets with gradient structures for different extrusion thicknesses were studied. The results implied that there was a pronounced gradient in terms of strain, grain size, and hardness across the sheet thickness. As the extrusion thickness was varied from 1.0 to 1.6 mm, the increasing thickness of the deformed coarse-grained layer contributed to decreases in the yield strength (YS) and ultimate tensile strength (UTS) and an increase in the elongation after fracture. As a result, the distribution of the gradient structure across the sheet thickness was controllable. There were considerable improvements in hardness, YS, and UTS and only a small reduction in elongation after fracture. In addition, after annealing at 150 °C, the hardness and tensile properties of the sheets were slightly different than those of the untreated sheets, indicating that the sheets had good thermal stability below this annealing temperature. Thus, PFM is an efficient SPD process for preparing the gradient structure sheets with high strength and reasonable ductility. • The formation mechanism of the pure copper sheets with gradient structure processed by plastic flow machining was analyzed. • The variation of the gradient structure of the pure copper sheets with different processing conditions was analyzed. • Thermal stability of the pure copper sheets was analyzed.