Ductile-brittle transition of pure Al-interlayer sandwiched by high strength Al alloy

Four point bending test (FPB) was conducted to investigate the unusual ductile-brittle transition (DBT) of pure Al sheet with decreasing thickness, sandwiched by 2024 alloy through explosive cladding. The results show that, with the decrease in thickness of Al-interlayer restricted by parallel interfaces, obvious differences appear for the measured load-displacement curves, and fracture toughness characterized by critical J integral drops down remarkably. Correspondingly, brittle cleavage patterns, mainly belong to {1 0 0} besides a very few {1 1 0}, were observed on the fracture surfaces and increase gradually in the fraction as decreasing in the thickness of Al-interlayer. A finite element simulation showed that the crack-tip plastic zone spreads rapidly in the Al sheet and advances along the ligament confined by the two interfaces. With either decreased thickness or increased load, the stress triaxiality and maximum principal tensile stress ahead of crack-tip continue to increase, which make the materials become more brittle.