Development of high strength Al–Mg–Si AA6061 alloy through cold rolling and ageing

Ultrafine grained (ufg) and nanocrystalline (nc) materials are widely researched due to significant improvements in yield and fracture strength. However, achieving a reasonable ductility in these materials is still a challenge. Recent results have shown that the combination of high strength and ductility could be achieved in precipitation hardening alloys through severe plastic deformation followed by annealing/ageing treatments. In the present work, the solutionised plates of an Al–Mg–Si alloy (modified AA6061 alloy) were subjected to severe cold rolling at room and liquid nitrogen temperatures to a true strain ∼1.6. The rolled sheets were aged to induce precipitation. The equilibrium second phase distribution for the above alloy was calculated using CALPHAD. The rolled and aged samples were analysed using differential scanning calorimetry (DSC), X-ray diffraction (XRD), transmission electron microscopy (TEM), hardness and tensile tests. The stored energy obtained from DSC measurements was found to be independent of the rolling temperature. The volume fraction of S {1 2 3} 〈6 3 4〉 orientation is predominant (∼40%) in both the rolling conditions. The strength and ductility were simultaneously improved following ageing of the cryorolled (CR) and room temperature rolled (RT) samples. Transmission electron microscopy analysis revealed dislocation cell structures in the CR and RT conditions. Analysis of second phases revealed fine spherical Mn rich precipitates (most likely Al6Mn) following ageing.