Effects of Sn content and hot deformation on microstructure and mechanical properties of binary high Sn content Cu–Sn alloys

The microstructure and phase-formation behavior of Cu–Sn alloys were investigated as a function of alloy composition; in addition, hot plastic deformation was performed at different cooling rates to evaluate the effect on the mechanical properties of the alloys. The microstructure of the as-cast Cu–Sn alloy consisted of a dendritic primary-α phase and an α+δ-Cu₄₁Sn₁₁ eutectoid phase. Hot plastic deformation performed at 750 °C induced a dynamic phase transformation from α+δ eutectoid into single bcc β-Cu₁₇Sn₃. Furthermore, the removal of pore defects, refinement of phases, and work hardening were introduced into the microstructure of the Cu–Sn alloys. For samples quenched after high-temperature processing, the atomic diffusion of Sn solutes in the β phase was suppressed due to the high cooling rate, leading to a diffusionless transformation of the β phase into the acicular-shaped β′-Cu_5.6Sn martensitic phase. Despite severe deformation, the Cu-22 wt%Sn sample, which contained a large amount of the β′ martensitic phase, exhibited improved hardness, tensile strength, and ductility.