Structural development during production of tubes from rapidly solidified aluminium alloy powder

Abstract

A range of tubes has been successfully produced from the fine air atomized powder of an Al–12Mg–0·8Mn alloy. The powder exhibited a cellular solidification morphology with cell boundaries containing a film of β –phase (Al₃Mg₂). Above 700 K, the phase transforms to Al₁₈X₂Mg₃ precipitates during the preheat before processing, but at lower temperatures the transformation takes place only in the deformation zones of the billet. The tube structure of fine precipitates and apparent grains or subgrains is built from the powder in the clearly defined deformation zones. The oxide envelope surrounding powder particles fragments during processing and could not be distinguished in the tube microstructure. The tube structure and properties were largely dependent upon the processing temperature and not the reduction ratio. Yield strengths of more than 500 MN m⁻² have been recorded, with ductilities of around 10%, which compares very favourably with conventional aluminium alloy tubes.

MST/336