Enhancing strength-ductility synergy in age-hardened Al-Mg-Si alloy via combined pre-ageing and pre-straining

A pre-treatment strategy via combined pre-ageing and pre-straining has been proposed to overcome the limitation of strength-ductility in Al-Mg-Si alloy. The dislocations and fine precipitates obtained by artificial pre-aging at 120°C for 12 hours followed by a 5% pre-strain before post-aging at 120°C resulted in an increase in elongation to failure by 91.2% and an increase in the yield strength of 22 MPa as compared to the conventional T6 alloy. Furthermore, the new method shortens the required post-ageing time at 120°C to the peak-hardness from 96 h in the solely pre-strained alloy to 24 h. Dense and fine pre-β" particles with a low lattice mismatch with the matrix are formed. Contrary to harder and larger β" phases in the T6 alloy, these tiny precipitates prevent local accumulation of dislocations at precipitates during tensile deformation. This inhibits dynamic dislocation recovery and thus prolongs the strain hardening. Our findings demonstrate the potential of fine tailoring of dislocations and precipitates in enhancing the properties in Al alloys.