Effect of tool temperature on mechanical properties and microstructure of thermo-mechanically processed AA6082 and AA7075 aluminum alloys

Abstract

The present work focuses on the effect of thermo-mechanical processing on the mechanical properties and microstructural evolution of AA6082 and AA7075 aluminum alloys using a novel forming process, i.e. integrating solution heat treatment, hot forming and tool quenching. Different tool temperatures ranging from 24 °C to 350 °C were applied to investigate their influence on mechanical strength and ductility. By using various tool temperatures, this study aims to provide insights needed for tailoring the mechanical properties of two different high-strength aluminum alloys. Further it is shown, how the different resulting cooling rates affect the final property distribution. Upon processing, uniaxial tensile tests were carried out at room temperature to characterize the mechanical properties of the investigated conditions. Microstructural investigation was further conducted by using scanning electron microscopy to reveal the prevalent deformation and strengthening mechanisms. Results obtained by mechanical testing reveal that reduction in tool temperature finally results in the realization of parts with higher strength upon aging. Tool temperatures above 200 °C deteriorate the strength of both alloys, however, improve ductility. Most importantly, the thermo-mechanical process used in the present work has only minor impact on the grain size of both alloys. However, the process appears to have a strong influence on the final morphology and size of precipitates. Elevated tool temperatures and, thus, lower cooling rates, make both alloys prone to the formation of coarse precipitates eventually deteriorating strength.