Microstructure evolution and thermal stability of L12-Al3Zr dispersoids in Al-X-Zr (X = Cu, Zn, Mg) aluminum alloys.

The impact of three main alloying elements (X = Cu, Zn, and Mg) on the precipitation evolution and structural stability of L1 2 -Al 3 Zr dispersoids in heat-resistant Al-X-0.2 wt% Zr alloys (4–5 wt% X) has been thoroughly examined experimentally. In line with earlier predictions, all three elements are found to be effective in promoting L1 2 precipitation during heat treatment at 500 °C, but with clearly different outcomes revealed: Zn is most effective in refining the dispersoid microstructure, Cu is most effective in increasing the L1 2 phase thermal stability, while Mg is promoting the precipitation kinetics the most strongly. These phenomena may be linked primarily to the different partitioning concentrations of the three elements within the L1 2 -Al 3 Zr dispersoids. It is observed that 11 ± 2. (at. %) Cu and 17 ± 2 (at. %) Zn, respectively, are incorporated in the particles, replacing Al atoms, while Mg incorporation appears marginal. The increased precipitation kinetics with Mg addition is evidenced by the dispersoid number density peaking much earlier in this alloy. This beneficial result however is hampered by primary Al 3 Zr particle formation, together notably limiting the number density. Both Cu and Zn can increase the energy barrier to anti-phase boundary (APB) activation, extending the L1 2 stability range. Cu is more effective as the Cu-APB repulsion is almost twice as strong as the Zn-APB repulsion, but theory predicts that this difference may be eliminated with higher Zn incorporation. These findings resolve the fundamental individual influence mechanisms of three key main alloying elements on the precipitation of Al 3 Zr dispersoids, which is essential for regulating the properties of various aluminum alloys. [Display omitted] • Cu, Zn and Mg are effective in promoting L1 2 precipitation during heat treatment. • About 10.6 ± 2.2 (at. %) Cu and 16.5 ± 1.7 (at. %) Zn are incorporated in the L1 2 -Al 3 Zr dispersoids. • Cu is more effective in promoting the stability of the L1 2 phase compared with Zn. [ABSTRACT FROM AUTHOR]