Microstructural Evolution and Mechanical Properties of Multi-layered Aluminum Alloy 6061 Processed by Accumulative Roll Bonding

This study investigates the enhancement of mechanical properties and changes in microstructure in a 6061 aluminum alloy processed through accumulated roll bonding (ARB), a severe plastic deformation process that generates ultra-fine grains. The ARB process was performed without lubrication at an elevated temperature (500 °C) for a maximum of five cycles. After the third cycle, distinct boundaries and ultra-fine grains (UFG) with a crystallite size of 30 nm were observed, which were further reduced to 17 nm after the fifth cycle. After undergoing five ARB cycles, the 6061 alloys exhibited a significant increase in tensile strength, reaching approximately 2.6 times their original value. However, elongation experienced a significant decrease following the first cycle and gradually decreased with subsequent cycles. Regarding hardness, the specimens subjected to one, three, and five cycles exhibited uneven variations along the normal direction, with non-uniform fluctuations. Notably, peak values were observed near the surface and at the center of the specimens. Wire brushing and shear strain were identified as the causes of this uneven hardness distribution. These findings suggest that the ARB method effectively refines and strengthens the grain structure of the Al6061 alloy.