Study On The Nanostructured Aluminum Alloy Processed By Dynamic Plastic Deformation And Its Microstructure Evolution Mechanism

1050commercial-purity aluminum and2195Al-Li alloy are processed by means of dynamic plastic deformation at room temperature with split Hopkinson pressure bar. Two means of loading methods are conducted, i.e. uni-directional impact and multi-directional impact with different accumulative strains of1.6and3.6respectively. The as-deformed microstructures are characterized, and the microstructural evolution mechanisms during high strain rate deformation are also discussed.The strain pulse signals recorded by an oscilloscope are calculated, the nominal strain rates of uni-directional impacted sample and multi-directional impacted sample are1.2×103s-1and2.8×103s-accordingly, while the periods of stress waves during deformation less than200μs. Dynamic stress-strain responses in deformation are studied, the considerably consistent increment of flow stress during each pass are measured in the uni-directional impacted sample; in contrast, the flow stresses of multi-directional impacted sample keep in stable ranges after the fifth pass.The as-deformed microstructures are characterized by transmission electron microscopy, it has been found that initial coarse grains are refined significantly. The main microstructures of uni-directional impacted samples are elongated grains, whereas equiaxed grains/cells dominate in the multi-directional impacted samples. High densities of dislocations are generated in the deformed samples and further evolve into different types of dislocation substructures, i.e. dislocation cells (DC) and dislocation tangle zones (DTZ). The multi-directional impacted sample possesses a higher density of dislocations which can be found from the wavy and blurred grain boundaries and cell walls, in addition, a significant fraction of grains contain tiny subgrains and cells interiors.Dynamic recovery is seriously suppressed during high strain rate deformation by the short loading periods, giving rise to high densities of dislocations which provide conditions for the further refinement of grains. GNBs and IDBs are formed in the uni-directional impacted samples, the space between boundaries decreases with the increment of accumulative strain; some elongated grains fragment into tiny equiaxed nano-grains with the effects of increasing flow stress. In the multi-directional impacted samples, constant shifts of impact directions lead to the intersections of dislocation substructures spread in multi-directions, subdividing the coarse microstructures into smaller and smaller scales, and finally realize the refinement of grains.