Dynamic Tensile Fracture Behaviours of Selected Aluminum Alloys under Various Loading Conditions

Experiments investigating dynamic tensile fracture were performed on the extruded rods of 2024-T4 and 7075-T6 aluminum alloys under varying loading conditions. The initial yield stress and fracture strain of 7075-T6 alloy obtained in spilt Hopkinson tension bar tests are higher than that of 2024-T4 alloy. But the initiation fracture toughness and spall strength of 2024-T4 alloy are higher than those of 7075-T6 alloy in three-point bending and plate impact experiments, which indicates that 2024-T4 alloy has better crack initiation tolerance and stronger spall failure resistance. Based on metallurgical investigations by using optical and scanning electron microscopes, it is revealed that the microstructure has a profound effect on the dynamic tensile fracture mechanism of each aluminum alloy. The 2024-T4 alloy is relatively brittle due to voids or cracks nucleated at many coherent CuMgAl2 precipitate phases in the grain interiors, and the fracture mode is predominantly transgranular. The 7075-T6 alloy exhibits relatively ductile fracture because voids or cracks growth is partly intergranular along the grain boundaries and partly transgranular by void formation around coarse intermetallic particles. The obvious differences of damage distribution and void coalescence mechanisms for 2024-T4 and 7075-T6 alloys under plate impact are also discussed.