Synergistic strengthening by nano-sized α-Al(Mn,Fe)Si and Al₃Zr dispersoids in a heat-resistant Al–Mn–Fe–Si–Zr alloy

Strengthening by dispersoids in Al alloys has been limited by either low number density or low volume fraction of dispersoids. In the present work, the influence of an addition of 0.28 wt% Zr on precipitation hardening behavior of AA3003 alloy subjected to different heat treatments has been investigated. A superior microstructure simultaneously consisting of nano-sized α-Al(Mn,Fe)Si and Al₃Zr dispersoids at peak-aged state was achieved by two different heat treatment regimes, ramp heating with a speed of 50 °C/h and isothermal aging at 400 °C. As a result, a substantial increase in yield strength of 30 MPa (43%) was achieved in comparison to AA3003 alloy. Meanwhile, the AA3003-Zr alloy exhibits excellent heat-resistance with a stable yield strength from 12h (106 MPa) up to 250h (107 MPa) during isothermal aging at 400 °C. This remarkable thermal stability was ascribed to the continuously hardening from Al₃Zr precipitation, which compensates the strength loss from α-dispersoid coarsening. Besides, TEM study shows that the precipitation kinetics of Al₃Zr is significantly enhanced compared with the reference binary Al–Zr alloy, which is attributed to the Si content in the alloy. This work proposes an effective method to design a low-cost heat-resistant Al alloy in mass production.