Influence of plastic deformation and Cu/Mg ratio on the strengthening mechanisms and precipitation behavior of AA2024 aluminum alloys

Effects of Mg Content on the Microstructural and Mechanical Properties of Al-4Cu-xMg-0.3Ag Alloys

“…Beyond, the initial Cu/Mg ratio effect, it was observed that since from the beginning of the artificial aging process there was a progressive increase in the hardness value trend for both of the alloys which is consistent with the previously reported literature [6,19,20]. The monotonic increase in hardness values can be related to the formation of several precipitation phases from the metastable Al matrix during the ageing process [6,19,20]. In general, the hardness increases with the increase in ageing time, reaching a maximum value (peak ageing point T6) and then progressively decreases with further ageing leading to so-called overaged point (T7).…”

“…Thus, the increase in hardness for the L-1.4Mg alloy specimen is attributable to the synergistic effect of co-precipitation phases, namely Al-Cu-and Al-Cu-Mg-based phases. Particularly, it is reasonable to assume that the age-hardening behavior of our studied alloy is strongly dependent on two microstructural parameters: the precipitates size and their distribution in the matrix [19]. From the viewpoint of precipitation hardening, it is well known that the peak ageing state is controlled neither from very fine nor very coarse precipitate distributions but by the virtue of the intermediate precipitate size which is distributed at the grain boundary and in the matrix.…”

“…Nonetheless, the S-phase can promote a significant precipitation hardening effect due to their semi-coherent nature. Furthermore, the semi-coherent precipitates can effectively generate a high strain field when compared to coherent or non-coherent precipitate [19][20][21][22][23]. Nevertheless, for the higher hardness values of the L-1.4 Mg alloy (as seen in Figure 1), the role of multiple precipitation phases at peak-aged state along with initial solid solution strengthening effect could be a key factor.…”

“…From XRD profiles, beside the matrix phase (Al), the additional peaks corresponding to the intermetallic phases were also determined for H-0.4Mg and L-1.4Mg alloys, respectively (as shown in Figure 5). These additional peaks could be identified as the Al 2 Cu (θ) phase (tetragonal structure, 14/mcm, a = 0.6066 nm, c = 0.4878 nm) and Al 2 CuMg (S) phase (orthorhombic structure, Cmcm, a = 0.400 nm, b = 0.923 nm, c = 0.580 nm) [19,22,23]. It is evident that the Al 2 Cu (θ) phase and Al 2 CuMg (S) phase co-exist in both high and low Cu/Mg ratio compositional scenarios.…”

“…Thus, based on our microstructure analysis, the main strengthening factor in the L-1.4Mg specimen is attributed to the existence and distribution of S (Al 2 CuMg) precipitates formed at peak-aged state. Another factor for the increase in the mechanical strength could be due to the larger atomic size of the Mg than the Al; the Mg atom can occupy the substitutional position in the lattice and can impart an effective solid solution strengthening effect [19].…”