Influence of ingot structure on properties of commercial purity aluminium under hot testing conditions

Abstract

The influence of the cooling rate variation induced microstructural changes, present throughout the cross-section of commercial scale direct chill cast rolling ingots, on the substructural and thus flow stress characteristics during subsequent hot deformation has been investigated. Ingots of an Al–0·3%Fe alloy were cast by direct chill (DC) and sand casting processes and their behaviour compared with commercially produced DC cast ingots. The hot working behaviour of these ingots, of different initial as cast structures, was studied using elevated temperature tensile testing to establish the flow stress dependence on subgrain size and to assess the effect of temperature and initial as cast structure on hot ductility. The room temperature mechanical properties of hot rolled and subsequently low temperature annealed Al–Fe alloys (Al–0·5%Fe and commercially produced ETIAL O) having different as cast structures were also determined. Microstructures were characterised using optical and electron microscopy and hardness testing was performed to assist in explaining the tensile data. Significant variation in mechanical properties, flow characteristics, and hot ductility was found for samples machined from as cast and hot worked slabs; these samples had retained the wide range of particle distribution parameters which reflect the dendrite arm spacing of the as cast materials and are essentially governed by the conditions prevailing during solidification.

MST/1266