Study on the microstructure and mechanical properties of bimodal H62 brass via cold rolling and annealing

Abstract

This study investigates the microstructure and mechanical properties of H62 brass through cold rolling and short-time annealing, with the aim of achieving a bimodal structure. The results demonstrate that cold rolling significantly enhances strength, with yield strength (YS) and ultimate tensile strength (UTS) increasing by up to 6.6 times and 61.2 %, respectively, compared to the annealed sample, albeit at the expense of reduced ductility. Superior combination of strength and ductility is obtained under short-time annealing at 400 °C for 5 min. Specifically, the H62–2.99-400 °C(5 min) specimen achieves an YS of ∼334.0 MPa, UTS of ∼477.9 MPa, and UE of ∼29.6 %. Microstructure characterization reveals that cold rolling refines grains to ultrafine grain scale, while short-time annealing treatment promotes the formation of a bimodal structure comprising coarse and ultrafine grains. The strengthening mechanisms include high dislocation density, grain refinement, and heterogeneous deformation-induced (HDI) strengthening via geometrically necessary dislocations (GNDs) at soft/hard region interfaces. Additionally, the transformation of the β phase into the α phase during annealing further enhances ductility. This study provides valuable insights into the design of heterostructured materials, suggesting that controlling rolling and annealing processes can be optimized to achieve superior mechanical properties.