Tailoring The Microstructure And Mechanical Properties Of Nanostructured 6061 Aluminum Alloy

Nanostructured 6061 aluminum alloy was prepared by cold rolling with a reduction of 90%.A good combination of strength and ductility was obtained with subsequent annealing treatment.Based on transmission electron microcopy,atom probe tomography,hardness and tensile test,the microstructure and mechanical properties of the nanostructured 6061 aluminum alloy was investigated,well revealing the effects of deformation and aging treatment on microstructure and mechanical properties of alloy.The contribution of grain boundary strengthening,dislocation strengthening,cluster strengthening and segregation strengthening to the nanostructured 6061 aluminum alloy were discussed and evaluated,which provides a new strategy and approach for the development of nanostructured aluminum alloy with unique properties.The main conclusions of this study are summarized as follows:(1)After 90% cold rolling,the microstructure of the solution-treated 6061 aluminum alloy transforms from equixed coarse grains to the laminated ultrafine grains with the mean boundary spacing of 130 nm.Meanwhile,a high-density dislocation was introducted in the grain interiors.A high strength but low plasticity was caused by the change of microstructure.The yield strength of the prepared nanostructured 6061 aluminum alloy is 393 MPa and the total elongation is 4.6%,much stronger but more brittle compared with the peak aged coarse-grained sample.(2)With artificial aging at 100℃-200℃ for 1 hour,the nanostructured 6061 aluminum alloy show superior mechanical properties with the maximum product of strength and elongation is 3895 MPa·%.Specifically,the sample after aging at 120℃shows a yield strength of 413 MPa and an elongation of 6.9%,while that after aging at150℃ shows a yield strength of 404 MPa and an elongation of 9.1%.With the increase of aging temperature,the boundary spacing of the laminated grains increases while the dislocation density significantly decreases.An obvious solute segregation at defects such as dislocations and grain boundaries can be observed in the nanostructured 6061 aluminum alloy sample aged at 120℃ and 150℃.Theoretical analysis indicates that the main strengthening contribution results from grain boundary strengthening and cluster strengthening,followed by dislocation strengthening.(3)Compared with the solution-treated 6061 aluminum alloy,the aging hardening rate of the nanostructured alloy is much faster,with less time to hardness peak and higher strength.Especially,after aging at 100℃ for 36 h,the sample exhibits the best combination of strength and plasticity.i.e.426 MPa and 10.2%.The yield strength increases by 33 MPa and the plasticity increased to about 2.2 times of the prepared nanostructured 6061 aluminum alloy.Grain boundary strengthening,cluster strengthening and precipitation strengthening are the main factors in the peak-aged nanostructured alloy.