A generic framework for tailoring microstructures and mechanical properties in extruded magnesium alloys via rotational strain porthole die extrusion: A case study on Mg-RE hollow profiles

Abstract

Controlling microstructural evolution and texture to improve mechanical properties and weld seam integrity in Mg-RE hollow profiles is a generic challenge in materials processing. To address this, a novel Rotational Strain Porthole Die Extrusion (RSPDE) technique was developed, introducing circumferential shear strain during extrusion to refine texture and enhance dynamic recrystallization. Using Mg-8.8Gd-3.8Y-1.0Zn-0.7Mn hollow profiles as a case study, the RSPDE process achieved finer grains in the matrix zone, narrowed the precipitation-free zone in the welding seam, and reduced basal texture intensity compared to conventional porthole die extrusion (CPDE). Although the weld seam remained somewhat weaker due to larger grain sizes and absence of β' and γ' precipitates, subsequent aging treatments improved tensile strength. These improvements, however, came with reduced ductility due to precipitate-dislocation interactions. Despite this trade-off, RSPDE produced more homogeneous microstructures, weaker basal textures, and superior weld seam quality than CPDE. Fundamentally, this work establishes a transferable framework that links controlled shear deformation to predictable microstructural refinement and texture control, enabling more informed process optimization and alloy design strategies. This generic approach thus offers predictive guidelines for structural design and optimization across a broad range of high-strength magnesium alloys.