Improvements in superplastic performance of commercial AA5083 aluminium processed by equal channel angular extrusion

An improvement in superplastic performance, as measured by elongation to failure, was achieved in an AA5083 aluminum alloy. Equal channel angular extrusion (ECAE) processing was performed on commercially available hot rolled AA5083 material, in order to refine the microstructure to achieve superplastic characteristics. The ECAE process offered several potential advantages in the processing of an SPF-grade aluminum alloy. The first was the ability to introduce a high level of energy into the structure through localized shearing, which developed a well-defined sub-grain structure and ultimately a refined microstructure upon recrystallization. Secondly, with ECAE there is the unique ability to achieve the desirable microstructure in bulk form without reducing the dimensions of the starting material, as is the case in conventional roll processing of SPF sheet materials. Total elongation of >350% was measured at a temperature of 550 degreesC and strain rate of 5x10(-4). This was an increase in elongation of over 150% compared to the same material processed by convention thermal mechanical processing (TMP) techniques, designed to produce a fine grain microstructure in sheet material. Past work on the same commercial AA5083 material using an appropriate TMP schedule, revealed <200% elongation was achievable at the same temperature and strain rate. Through conventional thermal mechanical processing (a series of heat treatments and hot and cold rolling steps), the minimum grain size achieved was typically limited to 10 <mu>m, but with ECAE an average grain size <2 <mu>m was produced, after the recovery heat treatment step.