Size Effect on Microstructural Evolution and Micromechanical Responses of Mechanically Bonded Aluminum and Magnesium by High-Pressure Torsion

The mechanical bonding of dissimilar metals though the application of high-pressure torsion (HPT) processing is developed recently for introducing unique ultrafine-grained alloy systems involving microstructural heterogeneity leading to excellent mechanical properties. Considering further developments of the processing approach and the produced hybrid materials, the size effect on microstructural evolution and micromechanical responses of the mechanically bonded Al–Mg systems is evaluated. In practice, processing by HPT is conducted at room temperature on the separate Al and Mg disks having 25 mm diameter under 1.0 GPa at 0.4 rpm, and the results are compared with the mechanically bonded Al–Mg system having 10 mm diameter. The Al–Mg disks having 25 mm diameter show a general hardness distribution where low hardness appears around the disk centers, and it increases at the disk peripheries. Nanoindentation measurements demonstrate that there is excellent plasticity at the edges of the Al–Mg system with 25 mm diameter. The Al–Mg system with both 10 and 25 mm diameters show a consistent trend of hardness evolution outlining an exponential increase of hardness with increasing equivalent strain. The results are anticipated to provide a conceptual framework for the development and scale-up of the HPT-induced mechanical bonding technique.