Microstructure and properties of extruded Al–6Mg–3Cr alloy prepared from rapidly solidified powder

Abstract

Experiments have been carried out to determine the relationship between processing, microstructure, and mechanical properties of an Al–6Mg–3Cr powder alloy consolidated by extrusion. Attention is focused on the microstructure of the powder and the subsequent changes that occurred during thermomechanical consolidation to a fully dense product. The powder microstructure was composed of aggregates of three equilibrium phases (Al₁₈Mg₃Cr₂, Al₃Mg₂, and Al₁₃Cr₂) which were uniformly distributed within an Al matrix. Preheating to the extrusion temperature by induction had very little effect on the microstructure. However, consolidation of the powder accompanied by significant structural changes occurred during passage through the extrusion shear zone. The extruded microstructure was found to be inhomogeneous with coarse and fine bands of precipitates throughout. The inhomogeneities of extrudate microstructure have been related to the original powder and were caused by the wide range in powder particle size. The structural heterogeneities adversely influenced the extrudate properties, in particular, fracture behaviour, which was highlighted in poor toughness and ductility in a direction transverse to the working orientation.

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