Boss formability of nano-structured aluminum alloys at elevated temperatures

Abstract

Together with conventional alloys, ultra-fine or nano-structured aluminum alloys were prepared by equal channel angular rolling (ECAR) and pressing (ECAP). Formability of cylindrical bosses was investigated by compression tests of a closed die. Finite element (FE) analysis was also carried out to investigate the effect of die friction on the forming behavior. Cylindrical bosses with the aspect ratio over three were formed in a closed die at elevated temperatures even under a frictional condition, although more uniform deformation was expected under a frictionless condition by the FE simulation. Boss formability increased with increasing temperature and decreasing strain rate, and fine structured aluminum alloys had superior boss formability to the conventional alloys. Near-net shape forming of a simplified cellular phone case was performed at elevated temperatures using a set of closed dies. A nano-structured aluminum alloy showed higher formability in all aspects of bosses, sidewalls and face thickness than conventional alloys.