Effect of Sc and Zr on microstructure and chemical milling surface roughness of 2024-T6 alloy sheets

Chemical milling is one of the most widely used processing methods for Al alloys in the aerospace and aircraft industries. The surface roughness significantly impacts the mechanical performance of chemically-milled products. Therefore, it is rational to develop a strategy to control the surface roughness. In this study, the effect of minor Sc and Zr additions on the microstructure and chemical milling surface roughness of a 2024-T6 alloy sheet was investigated. The additions optimized the surface roughness, and values of (0.7377 ± 0.0024) and (0.9053 ± 0.0018) μm in the rolling and transverse directions respectively, were achieved, which were significantly lower than those achieved by the 2024 alloy ((1.0785 ± 0.0026) and (1.2205 ± 0.0021) μm, respectively). The 2024SZ (2024-0.1Sc-0.2Zr Al) alloy exhibited fine and discontinuous grain boundary intermetallic particles (IMPs) in the as-cast state. Thermo-Calc software showed that the 2024 SZ alloy formed L12-Al3(Sc, Zr) phases during solidification, which induced heterogeneous nucleation and refined the grains. The weight fraction of IMPs in the 2024SZ alloy was much considerably smaller than that in the 2024 alloy during solidification. These IMPs affected the density of the IMPs in the T6 state. Finally, the mechanism of Sc and Zr on the chemical milling surface roughness of the 2024-T6 alloy was demonstrated. This study provides a feasible strategy for optimizing the chemically-milled surface roughness of Al alloys. [Display omitted] •Sc and Zr elements refine the IMPs of the 2024 Al alloys.•Addition of Sc and Zr elements optimize the chemical milling surface roughness of 2024 Al alloys.•The addition of Sc and Zr reduced the weight fraction of IMPs in the 2024 Al alloy during solidification.