Microstructure analysis of aluminum extrusion: grain size distribution in AA6060, AA6082 and AA7075 alloys

Microstructure and material flow of aluminum alloys have a significant influence on the mechanical properties and surface quality. In extrusion of aluminum billets at high temperatures the microstructure is dependent on the alloy and the forming and temperature history. A prediction of grain size and precipitation is of increasing importance in order to design the process by adjustment of parameters such as punch speed, temperatures, and quenching. To give references for microstructure prediction based on material flow, and with it strain and strain rate history, this paper deals with the microstructure during the extrusion process of AA6060, AA6082, and AA7075 alloys. Billets have been partly extruded to axisymmetric round profiles and the microstructure of the press rests consisting of the billet rests in container and die has been considered. Furthermore, these rests have been analyzed to show the material flow, dynamic and static recrystallization based on macro etchings and visible microstructure under different conditions, e.g. as in the area of high strain rate near the container wall, or in dead zones [1]. To allow an accurate simulation of the extrusion process, punch force and temperature conditions during the tests have been measured and are presented in this paper, too.