Thermomechanical Processing of Pure Magnesium: Hot Extrusion, Hot Rolling and Cold Drawing

TL;DR

This study systematically investigates the effects of hot extrusion, hot rolling, and cold drawing on pure magnesium's microstructure and mechanical properties, identifying optimal processing parameters for improved wire production.

Contribution

It provides a comprehensive analysis of thermomechanical processing parameters for pure Mg, highlighting the influence of extrusion ratio, rolling speed, and annealing on microstructure and formability.

Findings

Higher extrusion ratios produce bimodal grain structures with beneficial twins.

Faster rolling speeds result in finer microstructures.

Optimal annealing conditions improve ductility and deformation behavior.

Abstract

A comprehensive study on thermomechanical processing of pure Mg was conducted through sequential hot extrusion, hot rolling, and cold drawing operations. Three different extrusion ratios (6:1, 25:1, and 39:1) were investigated at 350{\deg}C, revealing that 39:1 ratio produced an optimal bimodal grain structure with beneficial twin morphology. Subsequently, hot rolling experiments were performed at varying linear speeds (26- and 130-mm s-1) and interpass annealing times (2.5 and 10 minutes). Results demonstrated that higher rolling speeds led to finer microstructure, while longer interpass annealing times resulted in reduced twin fraction and more inhomogeneous microstructure. The processed material was then subjected to cold drawing with approximately 12% true strain per pass. Different annealing conditions (275{\deg}C and 375{\deg}C for 2.5-10 minutes) between drawing passes were evaluated. Analysis showed that annealing at 375{\deg}C for 2.5-5 minutes provided optimal softening for subsequent deformation. Fracture analysis revealed a mixed ductile-brittle behavior, with twin-matrix interfaces serving as preferred crack propagation paths This study establishes optimal processing parameters for pure Mg wire production, highlighting the critical role of twin characteristics and restoration processes in determining material formability during multi-step thermomechanical processing.