Improving the strength and ductility of Al–Mg–Si–Cu alloys by a novel thermo-mechanical treatment

A novel thermo-mechanical treatment, composed of under-aging, cold-rolling and re-aging, has been developed to improve the strength and ductility of Al–Mg–Si–Cu alloys pronouncedly. The thermo-mechanically treated 6061 Al sheets exhibit much higher ultimate tensile strength and yield strength (being 560 MPa and 542 MPa, respectively) than those of the conventional peak-aged sheets (being 365 MPa and 348 MPa, respectively), while maintaining rather good elongation to failure and uniform elongation (being 8.5% and 7%, respectively). The microstructure analyses show that the high strength is attributed to a combination of precipitation strengthening, dislocation strengthening, sub-structure strengthening and high Taylor factor value and the good ductility is attributed to both the recovery process and the re-precipitation of the GP zones. Furthermore, the contributions of different strengthening mechanisms are quantitatively estimated.