Microstructural Evolution Of As-cast Research Articles

Influence of Erbium and Thermal Treatments on the Microstructure and Hardness of Al-Mg-Si Alloy

The influence of Erbium (Er) addition and thermal treatments on the microstructure and hardness of Al-0.5 wt.%Mg-1.0 wt.%Si alloy has been studied. Chemical composition of the alloys was measured by optical emission spectrometry (OES) and x-ray fluorescence (XRF). Microstructural evolution of as-cast, solution-treated, and aged samples were characterized by scanning electron microscope (SEM). The phase identification and elemental distribution were obtained from energy dispersive spectroscopy (EDS). From the microstructure, it was confirmed that solutionization at 570 ͦ C for 15 hours dissolved the Mg2Si and Er-rich intermetallics. However, some Fe-rich intermetallics remained after the solution heat treatment. Er addition had a role on the modification of β-AlFeSi and improved the hardness. Er-modified Al-Mg-Si alloy gave a significant improvement in mechanical properties. Therefore, Er is one of the candidate elements that could provide an opportunity for a high-strength Al-Mg-Si alloy.

Optimization of microstructure and properties of as-cast various Si containing Cu–Cr–Zr alloy by experiments and first-principles calculation

The CuCr0.8Zr0.12Six (wt.%, x = 0, 0.02, 0.05 and 0.2) alloys were designed and prepared by casting method. The function mechanism of Si content on as-cast microstructure evolution and properties was revealed with the guidance of thermodynamic analysis and first-principles calculation. Cr3Si tends to form during solidification at higher Si content due to its relatively low excess Gibbs free energy, which was proven to significantly affect the mechanical properties of alloys. The relationship between microstructure and mechanical properties of as-cast CuCr0.8Zr0.12Six alloy was also experimentally investigated. With Si content increasing from 0 to 0.2 wt%, the tensile strength and elongation of the CuCr0.8Zr0.12Six alloys simultaneously increase from 251 MPa to 29.0% in CuCr0.8Zr0.12Si0 to 268 MPa and 33.0% in CuCr0.8Zr0.12Si0.05, and then decrease to 229 MPa and 23.7% in CuCr0.8Zr0.12Si0.2. Simultaneously, the electrical conductivity and hardness of CuCr0.8Zr0.12Si0.05 respectively reach 57.2 %IACS and 85.1 HV, CuCr0.8Zr0.12Si0.05 was thus identified to be the best composition with relatively high comprehensive properties in this case.

Three-phase strengthening and toughening mechanism of MgY12Zn2.5 magnesium alloys

The microstructural evolution of as-cast, solid-solution-treated, extruded, and forged MgY12Zn2.5 magnesium alloys were observed, and the strengthening and toughening mechanisms of the deformed alloys were studied. The results showed that α-Mg solid solution was transformed into a lamellar structure of the 14H-LPSO + 2H-Mg phase, after solution treatment. The lamellar composite structure of the 14H-LPSO, 2H-Mg, and 18R-LPSO was formed by extrusion of the solid-solution-treated alloy and then a forging deformation. In the process of plastic deformation, the three-phase (2H-Mg, 14H-LPSO and 18R-LPSO) coordinated deformation and uniform distribution of the stress and strain, effectively restricting the stress concentration at the interface and delaying the initiation of cracks. The ultimate tensile stress (UTS), yielding tensile stress (YTS), and elongation of the MgY12Zn2.5 at room temperature were 415.0 MPa, 395.25 MPa, and 14.2%, respectively, reaching the level of the high-strength and high-toughness magnesium alloys.

Comparative Study of Hot Deformation Behavior and Microstructure Evolution of As-Cast and Extruded WE43 Magnesium Alloy

Under compressive testing at 400 °C and a strain rate range of 0.05–5 s−1, the hot deformation behavior and microstructure evolution of an as-cast (AC), as-extruded (with a bimodal grain structure (named as Ex-1) or a relatively uniform fine grain structure (Ex-2)) WE43 alloy have been investigated and compared. The results indicate that the AC sample exhibits the highest peak stress, while the Ex-2 sample has the lowest value. Within the AC material, fine grains were firstly formed along the pancake-like deformed grains (as a necklace structure). The necklace structure was also formed within the Ex-1 and Ex-2 materials at high strain rates of 0.5 and 5 s−1. However, a lamellar structure that the coarse elongated grains divided by parallel boundaries was formed within the Ex-1 material. A relatively more homogeneous fine grain structure is achieved after a true strain of 1.0 within the Ex-2 material at a low strain rate of 0.05 s−1. In addition, a discontinuous dynamic recrystallization mechanism by grain boundary bulging is found to occur. After a true strain of 1.2, a (0001) fiber texture, a typical rare earth (RE) texture, and a relatively random texture are formed within the AC, Ex-1, and Ex-2 WE43 alloy material, respectively.

As-cast microstructure characteristics dependent on solidification mode in TiAl-Nb alloys

In this work, as-cast microstructure characteristics are identified for the TiAl–Nb alloys with four typical solidification modes, namely, single β (B mode), hypo-peritectic (BA mode), hyper-peritectic (BAA mode) and single α (A mode) solidification. B mode alloys are chemically more homogeneous, and they show netty white ridge β-segregation and fine equiaxed lamellar grains compared to the other three mode alloys due to the β→α solid-phase transformation. Increasing Nb addition decreases the size of primary β dendrite and thus decreases the lamellar colony size of the B mode alloy. In BA and BAA mode alloys, much higher Al-segregation and worm-like β-segregation are formed in the interdendritic and dendritic regions, respectively. The low fraction and rapid growth of primary β dendrite in liquid and the subsequent peritectic α growth are responsible for the sharp casting texture and coarse lamellar colonies. A mode alloy is characterized by the columnar colony and weak casting texture due to the rapid growth of primary α dendrite accompanied by the lack of solid-state transformation refinement. As-cast microstructure evolution during cooling that depends on the phase transition sequence in the TiAl–Nb alloys with different solidification modes will also be proposed.

Microstructural evolution of as-cast Th–U alloys

Microstructural evolution of as-cast (arc-melted) microstructures of selected compositions of Th–U alloys is investigated. Characterizations are done using XRD, optical microscopy, SEM, TEM and hardness measurement. Microstructures vary from single phase to biphasic with increase in uranium content in thorium. Uranium is present as spheroids (<1 μm) or islands (∼7 μm) in high thorium (<10.7 wt.% U) alloys. With further increase in uranium content it forms an interconnected network of uranium rich phase and gets interspersed with similar network of thorium rich phase. High uranium Th–U alloys has dendrites of thorium dispersed in uranium rich phase. Grain size refinement of thorium rich phase is effective up to ≤10.7 wt.% uranium addition. Hardness of Th–U alloys increases with increase in uranium content. Comparatively lower hardness observed in Th–96U is due to presence of softer eutectic colonies in the microstructures. High thorium alloys have potentials for being utilized as dispersion type fuel with fissile uranium spread in thorium matrix.

Manufacturing process and electrochemical properties of an Mg–Ga–Hg anode sheet

Abstract The manufacturing process, electrochemical property, and microstructure evolution of as-cast, rolled, and annealed Mg-4.1% Ga-2.2% Hg anode sheet are studied in this investigation. The results show that the Mg-4.1% Ga-2.2% Hg anode sheet obtains an average discharge potential of −1.7924 V (vs. saturated calomel electrode) with an electric current density of 100 mA · cm−2 and a rapid activation time of less than 10 s in a half-cell test. The Mg–Ga–Hg sheet can be used as an anode material for seawater activated batteries. The Mg3Hg and Mg21Hg5Ga3 phases in the anode influence the electrochemical corrosion of the Mg–Ga–Hg anode sheet and provide a stable corrosion potential during discharge.