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A novel severe plastic deformation (SPD) route to achieve strengthening of AA 6061 alloy sheets by subjecting them to constrained groove pressing (CGP) followed by cold rolling (CR) is studied in the present work. Solutionized AA 6061 alloy sheets of 3 mm thickness have been subjected to CGP with an equivalent plastic strain of 1.16. The CGP samples have been subsequently cold rolled to reduce the thickness to 1mm (67% reduction) to achieve homogeneous microstructure with ultra-fine grains. It has been observed that yield strength increased significantly due to both CGP and CR. However, the ductility of the processed sample is lower. Therefore, an attempt has been made to study the aging behavior of the processed sample to achieve higher strength along with enhanced ductility through precipitation hardening. Aging of the processed samples was done by isothermal treatment at different temperatures. The microstructure of the deformed and aged samples was characterized by optical microscopy and scanning electron microscopy (SEM). Hardness and tensile tests have been studied to understand the mechanical behavior of deformed and aged samples. From the results, it has been found that processing of this alloy through CGP+CR and subsequent aging improves both strength and ductility due to the combined effect of precipitation hardening and recovery.

In the present work, cold rolling and cryo-rolling were performed on 99% commercially pure copper substrates. Both cold and cryo-rolling processes caused severe plastic deformation that led to an increase in dislocation density by 14× and 28× respectively, as compared to the pristine material. Increases in average tensile strengths, by 75% (488 MPa) and 150% (698 MPa), were observed in the two rolled materials as the result of the enhancement in dislocation density. In addition to strength, enhanced antibacterial property of cryo-rolled copper was observed in comparison to cold rolled and pristine copper. Initial adhesion and subsequent proliferation of bio-film forming Gram-positive bacteria Staphylococcus aureus was reduced by 66% and 100% respectively for cryo-rolled copper. Approximately 55% protein leakage, as well as ethidium bromide (EtBr) uptake, were observed confirming rupture of cell membrane of S. aureus. Inductively coupled plasma-mass spectroscopy reveals higher leaching of elemental copper in nutrient broth media from the cryo-rolled copper. Detailed investigations showed that increased dislocation led to leaching of copper ions that caused damage to the bacterial cell wall and consequently killing of bacterial cells. Cryo-rolling enhanced both strength, as well as antibacterial activity, due to the presence of dislocations.

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