Material Characterization of Extruded Aluminum Axial Tubes as Energy-Absorbing Structural Members

The increasing use of aluminum alloy extrusion in automotive vehicle chassis as structural members has necessitated the need to investigate their crushing behaviors. This article experimentally examines in detail, for the first time with respect to strength, ductility, and microstructure, AA6063-T7 (overaged) condition and the standard T6 temper and their capacity to meet crashworthiness requirements. Both tempers were assessed based on their mechanical properties (strength, ductility, true stress/strain behavior to necking, plastic anisotropy, strain rate sensitivity, and post-instability ductility to fracture) and microstructure, which were determined using basic tensile testing methods and metallographic approach. The implications of these properties/microstructures were further assessed experimentally by investigating the crushing behavior and energy absorption capacities of two extruded geometric profiles: a general rectangular profile and a novel cross-shaped profile investigated in a previous study. Typical modes of collapse were observed for rectangular tubes. In the case of the cross-shaped tubes, geometric modifications in the form of horizontal grooves along the sidewalls were introduced to promote controlled, stable, and repeatable folding patterns during the collapse in addition to serving as peak force reducers. It was concluded that the basic tensile test data recorded up to the point of necking failed to describe accurately the performances of both tempers (T6 and T7) of AA6063 alloy. The post-instability data of the alloys served as a better predictor of material behavior in assessing the crashworthiness of tubes under axial compression. Furthermore, novel cross-shaped tubes outperformed conventional rectangular shaped tubes and showed tremendous potential as energy-absorbing members for applications where weight savings is desired by using aluminum alloys over steel alloys.