Microstructure and mechanical properties of aluminum 5083 processed by equal channel angular extrusion

Abstract

The objectives of this research were to process commercial Al - 5083 using equal channel angular extrusion routes A, B, and C, include intermediate solution-heat treatments, investigate the room temperature and superplastic properties at high and low temperatures, and attempt to explain performance differences through analysis of grain and particle morphology and microtexture data. Precessing first at the hot working temperature of 300 C to a strain of ~ 4.6 was found necessary to sufficiently soften the microstructure and prevent shear localization failure during susequent processing at 200 C and 170 C to a cumulative processing strain of ~ 13.8. Regardless of extrusion route, an intermediate solution-heat treatment at 530 C following a processing strain of ~ 9.2 was found necessary to enhance both the room temperature and superplastic performance. At room temperature, route B provided the highest yield and tensile strength and route A the most ductility. At the conventional superplastic forming temperature of 510 C, route A had a flow stress almost independent of strain and the highest elongation to failure, route C strain hardened with an elongation to failure 15% less than route A, and route B had an immediate and sharp yield stress, nearly twice that of A and C, and an elongation to failure almost half that of route A. For the route A schedule, a one-hour intermediate solution heat treatment was found to provide the best superplastic performance. In this case, conventional superplasticity was achieved with elongations to failure of over 400% and a strain-rate sensitivity index of 0.35. Low-temperature superplasticity was investigated at 350 C but only marginal superplasticity was achieved with elongation to failure over 250% and a strain-rate sensitivity of 0.23. The measured particle volume fraction of 0.02 was insufficient to edequately stabilize the submicron grain size microstructure against grain growth at both 350 C and 510 C. Particle sizes greater than 0.56 um had an adverse effect on superplastic performance. Route B produced the largest particles and route A the smallest. Deformation microtexture evolution of route A indicated a progressive increase in misorientation angle and smearing of texture as deformation strain increased.