An aging processing design scheme derived from precipitation thermo-kinetic synergy of heat-treatable aluminum alloys

Abstract

Determination of ideal aging processing is crucial for developing heat-treatable aluminum (Al) alloys with good mechanical performances. To make full use of the advantages of precipitation, in the present work, we firstly established a yield strength model from the perspective of thermo-kinetic synergy. Then, we proposed a two-steps scheme to design the aging processing of the heat-treatable Al alloys. By taken the 6xxx Al alloys as representatives, in the first-step, the optimal aging time ($t_p$) at a given temperature, which derives from a high energy barrier for β” precipitation, is determined from the plateau endpoint of system energy dissipation curve. In the second-step, the optimal aging temperature ($T_A$), which originates from a large driving force for β” precipitation, is determined as the transition point from the Guinier-Preston (GP) zones to the β” phase. The rationality of this scheme was verified via the model system of Al-1.0Mg-0.6Si alloy, the precipitation behaviors of which have been well studied. Finally, we applied this scheme to the Al-0.46Mg-1.04Si alloy, whose optimal aging processing parameters are determined as $T_A$ = 438 K and $t_p$ = 9.37 h. Subsequent parallel experiments confirmed that the alloy samples aged at this pre-designed aging processing condition behaves the highest yield strength of ${\sigma }_y$ = 279.20 MPa, agreeing well with the predicted value of 275.80 MPa from the present strength model. We further extended the applications to the 2xxx Al alloys. The predicted ideal aging processing parameters (3.50 h at 438 K) and the according yield strength (399.57 MPa) for the Al-4.62Cu alloy are in accordance with the experimental results. Our investigation provides an insightful guidance for designing the advanced Al alloys with high strength from the perspective of precipitation thermo-kinetic synergy.