Role of annealing duration on grain distribution and fracture mechanisms in Zn–Mn alloy

The transition of inherently brittle materials to a ductile-plastic state is a persistent challenge in HCP alloy design. This work demonstrates a tailored thermomechanical processing route that successfully achieves this transition in a Zn-Mn alloy. An optimal schedule comprising 3 h homogenisation at 390 °C followed by 3 h annealing at 400 °C for a Zn-2.4Mn alloy produces a refined microstructure, a reducing grain size from 263.3 μm in the as-cast alloy to 45.0 μm in the annealed alloys. X-ray diffraction analysis confirms a 2.09 % lattice volume expansion and a 23 % reduction in dislocation density, indicative of a dominant recovery process counterbalanced by solute-induced strain. This ‘constrained recovery’ state yields a superior strength–ductility synergy: the bulk tensile modulus increases to 46.9 GPa, while nanoindentation hardness reduces to 1.06 MPa. The balance between discontinuous dynamic recrystallisation (DDRX), solid-solution strengthening, and controlled intermetallic formation is shown to govern the final mechanical properties. The established processing window provides a validated pathway for manufacturing components requiring damage tolerance, with direct applicability in precision-cast structural and bioresorbable systems.

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