Microstructure and micromechanism maps to optimise useful deformation processing conditions in magnesium alloy

Abstract

The present investigation examines the use of microstructure and micromechanism maps to develop a systematic understanding of the various microstructures that evolve in pure Mg and Mg–Al–Ce alloys during uniaxial compression deformation over a range of strain rates and temperatures. These maps further refine the safe deformation regimes that are predicted by dynamic materials modelling maps (or process modelling), which are based on efficiency of power dissipation for microstructure evolution η and the instability parameter Σ(). Operating mechanisms such as dynamic recrystallisation, cracking, twinning and grain coarsening are identified through careful microstructural analysis and mapped as a matrix at appropriate locations on a two-dimensional strain rate–temperature map. The study demonstrates that while conventional process maps delineate safe and unsafe working regimes based on power dissipation, it is the use of the microstructure and micromechanism maps in conjunction with the process maps that provide a more accurate and comprehensive picture of the processing window, which should be used for producing materials with certain defined end use. The process maps developed have been validated with a limited number of extrusion trials on pure Mg and Mg–Al–Ce alloys.