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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-Al 2 Cu and hcp Zn phases, thereby increasing the concentrations of Zn and Cu species in the Al matrix. During aging, two resistivity peaks (I R , II R ) become visible followed by the appearance of the related hardness peaks (I H , II H ). 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 I R peak, while the latter process produces the I H peak. During transformation of the ellipsoidal GP zones to hcp Zn, GPI zones are additionally formed, leading to the appearance of II R . The following transformation of the GPI zones into the θ''-Al 3 Cu phase leads to the appearance of the II H peak. Both the ellipsoidal GP zones and hcp Zn phases contain large quantities of Cu atoms, while the θ''-Al 3 Cu 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. [ABSTRACT FROM AUTHOR]

The effects of ultrasonic melt treatment (UST) and solution treatment on the microstructure and mechanical properties of a low-density multicomponent Al 70 Mg 10 Si 10 Cu 5 Zn 5 alloy at room and elevated temperatures were investigated. The as-cast Al 70 Mg 10 Si 10 Cu 5 Zn 5 alloy was composed of an fcc Al solid-solution, coarse secondary phases (5–30 μm), fine Cu-containing precipitates (<1 μm), and Zn clusters (<20 nm). The UST significantly reduced the porosity and size of primary Mg 2 Si particles and grains, resulting in an improvement in the strength and ductility of the as-cast alloy at 25 and 350 °C. The solution treatment at 440 °C caused the dissolution of hcp Zn and fine Cu-containing precipitates. It also resulted in the formation of Zn and Cu clusters in the supersaturated Al solid-solution at 25 °C, which led to an improved room-temperature strength. A phase transformation from Mg 2 Si to Q-Al 5 Cu 2 Mg 8 Si 6 occurred during the solution treatment along with the spheroidization of coarse secondary phases and grain growth, which deteriorated the ultimate compressive strengths at 25 and 350 °C and improved the ductility. Unlike the commercial Al alloys, the Al 70 Mg 10 Si 10 Cu 5 Zn 5 alloy showed excellent strengths at temperatures below 200 °C. This is attributed to the combined strengthening by coarse secondary phases, fine precipitates, and clusters. [ABSTRACT FROM AUTHOR]

We investigated the microstructural evolution and precipitation behavior of a multicomponent Al 83 Zn 5 Cu 5 Mg 5 Li 2 alloy using transmission electron microscopy (TEM) and atom-probe tomography (APT) during solution treatment, cooling, and natural aging. The as-cast alloy consisted of high volume fractions of V-Al 5 Cu 6 Mg 2 and η -Mg(Zn,Cu,Al) phases, which were partially dissolved during solution treatment at 450 °C. Slow furnace cooling (FC) after solution treatment resulted in the formation of polygonal V-phase, elongated η -phase, and platelet Y-phase precipitates. The Y-phase precipitates consisted of one Mg-rich central layer and three adjacent Zn/Cu-rich layers, both lying on the {111} Al planes. Instead of Y-phase precipitates, air cooling (AC) induced the formation of S- and Zn-phase precipitates with well-developed orientation relationships. No precipitation occurred during water quenching (WQ). The microhardness increased significantly during the natural aging of the AC and WQ alloys, whereas no hardening was observed in the FC alloy. TEM and APT analyses demonstrated that the natural aging induced the formation of fine solute clusters with a chemical composition of 52.3Al–21.3Li–18.3Zn–4.9Mg–3.1Cu (at%), contributing to the natural age-hardening of AC and FC alloys. The solute clusters were fully coherent with the Al matrix and exhibited an interfacial region rich in Zn and two central regions rich in Li and Zn. • Al 83 Zn 5 Cu 5 Mg 5 Li 2 cast alloy consists of highly interconnected V and η phases. • Cooling rate-dependent precipitation of V-, η-, Y-, S-, and Zn-phases is confirmed. • Y-phase comprises a Mg-rich layer and adjacent Zn/Cu-rich layers lying on {111} Al. • Li- and Zn-rich coherent solute clusters contribute to natural age-hardening. [ABSTRACT FROM AUTHOR]

This paper shows that the addition of transition elements significantly influences the microstructure and tensile properties of Al–12Si alloy cast under ultrasonic melt treatment (UST). The alloys contained primary Si, eutectic Si and a variety of intermetallic compounds (IMCs); the addition of Mn and Ni changed the solidification sequence by forming primary α-Al 15 (Fe,Mn) 4 Si 2 and ε-Al 3 Ni prior to primary Si formation. The primary Si and primary IMCs competitively consumed the nucleation sites introduced by UST, thereby influencing their refining efficiencies; the efficiency of primary Si refinement by UST increased with increasing the fraction of primary Si formed prior to IMC formation, whereas it deteriorated with increasing primary IMC fraction. The refining efficiency of eutectic Si and eutectic IMCs was not affected by the type and fraction of the primary phase. Using a Ti sonotrode for UST caused Ti contamination, resulting in grain refinement by forming Ti(Al,Si) 3 particles and increasing the amount of Ti solutes. Regardless of transition elements content, the application of UST improved the tensile strength at 25 °C and 350 °C. The refinement of IMCs caused by UST allowed the alloy to contain more IMCs without deterioration of room-temperature tensile strength. This enhanced the increment of high-temperature tensile strength by IMCs. Ductility of heavily alloyed systems was also improved by UST. [ABSTRACT FROM AUTHOR]