Ductile to brittle transition of inter pure AL sheet constrained by parallel bi-interface with high strength Al alloy

The ductile to brittle transition (DBT) in constrained Al sheet was investigated by experimental and numerical methods with its decreasing thickness, h, sandwiched by 2024 Al alloy through explosive cladding. The results clearly show that this transition has taken place characterized by different load deflection curves and decreasing fracture toughness, i.e. critical J integral. Correspondingly, fracture surface morphology develops from typical dimple type to brittle cleavage patterns appearing. And brittle cleavage patterns, mainly belong to {100} facets besides a very few {110}. Finite element calculations shows that during the loading process there is always a yield zone in Al interlayer constrained by neighboring elastic substrates. It is this growing region that results in increasingly high triaxial tensile stress and makes materials more brittle. The thickness scale in inter Al layer plays a key role in determining peak stress triaxiality. TEM analysis shows that Al interlayer has an obvious {100}<110> preferred orientation due to cold rolling process, the grains band width reaches about 1μm. This texture has an obvious effect on local cleavage fracture features. In micro mechanisms dislocations pile-up against grain boundaries around crack tip is remarkably enhanced as h decreasing, while it is little in bulk metal, which is assumed to be the root source resulting in ductile to brittle transition.