The material characterization and mechanical behaviors of aluminum alloy (6063) were investigated using flat specimens and the butterfly specimens with a modified Arcan fixture. The butterfly specimens were tensile-loaded at various stress triaxiality by changing the loading angles of the Arcan fixture. The flat specimens were tensile-loaded at various strain rates. The results of tensile tests at various stress triaxiality showed that the curves of engineering stress-engineering strain are obviously different. The results of different strain rates tensile tests showed that the yield stress and fracture stress increased slightly with strain rates increasing, however the fracture strain decreased obviously with strain rates increasing, and the ultimate strength almost remained constant. The Johnson-cook constitutive model could be used to describe the dynamic axial crashing behavior of thin-walled 6063 aluminum alloy tubes under impact loading. The material constants of the Johnson-cook constitutive model and failure model were acquired to be used for FEM simulation through material characterization.