Temporal evolution of precipitates in multicomponent Al-6Mg-9Si-10Cu-10Zn-3Ni alloy studied by complementary experimental methods

The precipitation behavior of the multicomponent Al-6Mg-9Si-10Cu-10Zn-3Ni (wt%) alloy was investigated during artificial aging at 120 °C through complementary experimental methods including hardness and electrical resistivity measurements, compression testing, differential scanning calorimetry, and transmission electron microscopy. The solution treatment causes the dissolution of the preexisting θ-Al2Cu and hcp Zn phases, thereby increasing the concentrations of Zn and Cu species in the Al matrix. During aging, two resistivity peaks (IR, IIR) become visible followed by the appearance of the related hardness peaks (IH, IIH). Spherical Guinier-Preston (GP) zones are formed first and then subsequently transformed into ellipsoidal GP zones. The former process results in the appearance of the IR peak, while the latter process produces the IH peak. During transformation of the ellipsoidal GP zones to hcp Zn, GPI zones are additionally formed, leading to the appearance of IIR. The following transformation of the GPI zones into the θ''-Al3Cu phase leads to the appearance of the IIH peak. Both the ellipsoidal GP zones and hcp Zn phases contain large quantities of Cu atoms, while the θ''-Al3Cu phase does not have any Zn atoms. Based on these insights into the structural and chemical compositional evolution of complex precipitates, the strengthening mechanism of the multicomponent alloy during aging has been established.