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A mechanism describing the synergistic effect of ultrasonic melt treatment (UST) and subsequent fast cooling on the refinement of primary Si particles in a hypereutectic Al−Si alloy was investigated by examining inoculant particles via high-resolution transmission electron microscopy, serial sectioning, and melt filtration. The application of UST activated non-wetting MgAl 2 O 4 particles with diameters of ∼0.5 μm to nucleate the primary Si phase. The cavitation-enhanced wetting of MgAl 2 O 4 particles caused the formation of the AlP phase at the MgAl 2 O 4 interface, further improving the nucleation potential. The cavitation-enhanced wetting and dispersion of inclusions (such as MgAl 2 O 4 ) also resulted in the refinement and de-agglomeration of AlP particles. The UST-induced changes to the inoculant particles ultimately increased their number density, and the observed effects became more pronounced after increasing the degree of undercooling up to 20 K, leading to enhanced refinement of primary Si particles at higher cooling rates (up to 10 2 K s −1 ). [ABSTRACT FROM AUTHOR]

The effects of aging temperature (25–220 °C) on precipitation behavior and the resulting alloy strength were characterized for the Al–6Mg–9Si–10Cu–10Zn–3Ni (wt%) natural composite. At an aging temperature of 25 °C, spherical and ellipsoidal Guinier–Preston (GP) zones (Zn clusters) are formed within the Al matrix. The fastest kinetics of Zn clustering is exhibited at 70 °C, which is caused by the combined effects of accelerated Zn diffusion and decreased phase thermal stability with increasing aging temperature. Thus, the Zn clusters and precipitates are formed prior to those of Cu (GPI and θ'') at 70 °C. As the precipitation kinetics of θ accelerates and Zn decelerates at above 70 °C, the precipitation sequence changes at 170 °C; clusters and precipitates of Cu are formed prior to those of Zn at this temperature. At an aging temperature of 220 °C (above the solvus of hcp Zn), θ'-Al 2 Cu and Q′-Al 4 CuMg 6 Si 6 phases are mainly precipitated instead of Zn clusters and precipitates. The matrix strengthening induced by the fine clusters and precipitates that form below 70 °C results in a significant improvement in the strength of the composite. However, high-temperature aging has only a small strengthening effect due to the lower matrix hardening caused by precipitate coarsening and the softening caused by the decreased volume fraction and spheroidization of the secondary phases. [ABSTRACT FROM AUTHOR]

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]

Crack propagation in high-Mn steel was investigated using in situ transmission electron microscopy. Preferential slips developed in the early stages of deformation on {1 1 1}, followed by the formation of a crack, which propagated along the pre-developed slip traces. A sharp corner was observed at the crack tip along two adjoining {1 1 1} planes. Surface ripples developed when the tip of the crack crossed pre-existing twins on the crack path, which was frequently observed in the surface during the final stage of fracture. [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]