Mechanical properties and corrosion behaviors of (Sc, Zr) modified Al-Cu-Mg alloy

To develop high-strength and excellent corrosion resistance Al-Cu-Mg alloys for aircraft skins in aerospace, this study investigated the mechanical properties, corrosion behaviors, and microstructures of 2024 (Al-3.78Cu-1.27 Mg) and 2024SZ (Al-3.74Cu-1.17 Mg-0.1Sc-0.2Zr) alloys. The results show that the (Sc, Zr) modified as-cast 2024SZ can transform the primary dendrite α-Al phases to equiaxed crystal, refine matrix grain with the diameter reduced from 186.07 μm to 34.67 μm in the as-cast state, and prevent the formation of crystalline phase during the solidification. The experimental data shows that the minor Zr and Sc additions can optimize the mechanical properties by promoting S (Al2CuMg) phases precipitation and inducing the Al3(Sc, Zr) particle strengthening mechanism after peak aging treatment. The yield strength of the 2024SZ-T6 alloys increased from 287 ± 5 MPa to 313 ± 4 MPa at the expense of a small loss in elongation (decreased from 18.9 ± 0.12% to 16.7 ± 0.11%), as compared to the Sc, Zr free alloy. Moreover, the corrosion resistance of 2024SZ-T6 alloys was enhanced (the IGC depth of 2024SZ-T6 alloys decreased from 166.6 μm to 62.1 μm). This was attributed to the nano-scaled coherent Al3(Sc, Zr) (diameter 11 nm) dispersoids, which refined grain boundary, inhibited recrystallization, and reduced the precipitate free zones (PFZ) of the 2024SZ-T6 alloy. The present investigation systematically and comprehensively revealed the effects of S phases, Al3(Sc, Zr) phases, and grain boundary dispersoids (GBs) on the strengthening mechanism and corrosion mechanism in Al-Cu-Mg alloy.