Crash-worthiness of a recently-developed AA 2624 aluminum alloy: Experimental studies

Abstract

In this study, the crash-worthiness of a recently-developed AA 2624-T351 aluminum alloy plate was experimentally determined under dynamic compressive load along the normal (OP) and rolling (IP0) directions of the as-received plate. The alloy is characterized by anisotropic grain shape with an aspect ratio of 9:3:1 (RD:TD:ND). While IP0 specimens exhibit higher true strain and true strain-rate than those of the OP specimens, the latter exhibit higher dynamic impact strength than the former due to lower grain thickness of OP specimens (tOP) than that of IP0 specimens (tIP0). The strain-rate sensitivity, m, increased as deformation rate changed from the quasi-static (mOP = 0.0059 and mIP0 = 0.0023) to dynamic regimes (mOP = 0.25 and mIP0 = 0.19). At strain rates above 6070 s-1, the m value for IP0 specimens dropped significantly to -0.57 due to the formation of adiabatic shear band (ASB). While the deformation mechanism in AA 2624-T351 alloy is slip, the onset of dynamic fracture is preceded first by the saturation of <110>||CD fiber texture on the compression plane. This is followed by (a) the onset and exhaustion of slip bands (~7 μm thick), (b) onset and propagation of ASB, and (c) dynamic fracture along the ASB. These mechanisms hold for both OP and IP0 specimens but occur at a much lower impact momentum, true strain and true strain-rate in OP specimens due to their smaller grain thickness, tOP. This implies that the IP0 specimens exhibit better damage tolerance under dynamic impact loading than the OP specimens. Unlike the conical-shape ASB developed in equiaxed grained aluminum alloys, two unconnected, split ASB cone develops in AA 2624-T351 plate; a behavior that could open new ways of engineering the microstructure of alloys to resist ASB propagation. By comparison, the recently-developed AA 2624-T351 alloy has improved dynamic mechanical strength and better crash-worthiness than the more widely-used AA 2024-T351 alloy.