Optimizing bendability and hardness of age-hardenable aluminum sheets through local thermo-mechanical processing

Abstract

This paper introduces a novel thermo-mechanical process to modify the local formability and hardness of 6xxx aluminum (Al−Mg−Si−Cu) alloy sheets in T4 and T6 tempers. In this process, two pairs of rollers travel along the length of a sheet while locally bending and unbending it so that the final shape and thickness of the sheet remains unchanged. It is possible to apply local deformation and/or heating with the process and control the properties separately. Room temperature bending/unbending (B/U) produces a deformation gradient through thickness and local hardening in both T4 and T6 sheets (with 38 % and 15 % greater Vickers hardness, respectively). High temperature B/U performed at ∼ 500 °C via induction heating, produces T4-temper-level bendability (bend angles of ∼ 150°) within the high temperature B/U processed zones of T6 sheets, without disturbing the T6 temper in the remainder of the sheet. T4 sheets benefit from the B/U deformation more than the T6 sheets, and the process offers increased local hardness of T4 sheets without significant loss in formability mainly due the heterogenous microstructure development and the weakened Cube texture through thickness. Individual control of local bendability and hardness in both tempers can enable downgauging and increase their usage in automotive applications.