Microstructure Of As-cast Alloy Research Articles

Effect of Zr modification on solidification behavior and mechanical properties of Mg–Y–RE (WE54) alloy

Abstract Magnesium alloys containing rare earth elements (RE) have received considerable attention in recent years due to their high mechanical strength and good heat-resisting performance. Among them, Mg–5%Y–4%RE (WE54) magnesium alloy is a high strength sand casting magnesium alloy for use at temperatures up to 300 °C, which is of great interest to engineers in the aerospace industry. In the present work, the solidification behavior of Zr-containing WE54 alloy and Zr-free alloy was investigated by computer-aided cooling curve analysis (CA-CCA) technique. And the solidification microstructure and mechanical properties of them were also investigated comparatively. It is found from the cooling curves and as-cast microstructure of WE54 alloy that the nucleation temperature of α-Mg in WE54 alloy increases after Zr addition, and the as-cast microstructure of the alloy is significantly refined by Zr. While the phase constitution of WE54 alloy is not changed after Zr addition. These phenomena indicate that Zr acts as heterogeneous nuclei during the solidification of WE54 alloy. Due to refined microstructure, the mechanical properties of Zr-containing WE54 alloy is much higher than Zr-free WE54 alloy.

Microstructure and hydrogenation kinetics of Mg2Ni-based alloys with addition of Nd, Zn and Ti

In order to enhance the hydrogen absorption kinetics of the Mg2Ni-based alloys, metal elements (Nd, Zn, and Ti) were added during melting process, respectively. The Mg2Ni-based alloys were melted using an electric resistance furnace under the protection of the covering reagent to prevent the oxidation and the evaporation of magnesium. Phase compositions and microstructures of as-cast alloys were characterized by XRD and SEM equipped with EDS. Hydrogenation kinetics of experimental alloys were investigated by the constant volume method using a Sievert-type apparatus. The addition of Nd, Zn or Ti elements to Mg2Ni results in the formation of minor phases Mg6Ni and Ni3Ti. Nd and Zn are dissolved in α-Mg, Mg2Ni and MgNi2 phases in Mg2Ni-based alloys. With the addition of Nd, the hydrogen content of the first absorption is 2.86% in mass fraction, which is higher than that of the Mg2Ni. Hydrogen absorption kinetics and activation properties of Mg2Ni-based alloys are improved evidently. During the initial three hydrogenation/dehydrogenation cycles, the hydrogen absorption capacity and kinetics properties have been improved for alloys with the addition of transition element Zn or Ti. The kinetics properties of the experimental alloys and absorbing reaction mechanism were also analyzed with the help of the Hirooka kinetics model.

Heat Treatment of AZ91D Mg-Al-Zn Alloy: Microstructural Evolution and Dynamic Response

Magnesium alloys are attracting great interest from the automotive industry because of the potential for weight reduction. An AZ91D cast alloy was studied in the current work to understand the effect of heat treatment on the microstructure and dynamic compressive properties. The selected heat treatments include solution treatment (T4) and solution treatment followed by aging (T6). The as-cast alloy microstructure consists of intermetallic β-phase (Mg17Al12) precipitates surrounded by α + β lamellar eutectic in α-Mg solid solution. The AZ91D-T4 specimens showed small β-phase precipitates along the grain boundaries and regions of eutectic mixture. The T6 heat treatment causes the β-phase platelets in the α + β eutectic to grow and develop into β-precipitates. The difference in the phase morphology reflects into the mechanical properties. The Vickers hardness of the T6 heat-treated specimens was 3.6% higher than the as-cast alloy. The compressive yield strengths of T4 and T6 treated specimens were 1.3% and 43.1% higher than those of as-cast specimens. The high strain rate compression testing resulted in increase in the strength with strain rate for the T4 and T6 specimens. A maximum increase of 42% was observed in T6 specimen tested at a strain rate of 4,000/s in comparison to the quasi-static compression. Under high strain rate compression testing, the T6 heat-treated specimens showed failure of the β-precipitates resulting in increased energy absorption in comparison to the quasi-static compression.

Effect of trace La addition on the microstructure and mechanical property of as-cast ADC12 Al-Alloy

The effects of addition of La on the microstructure of as-cast ADC12 Al-Alloy were investigated by using optical microscope (OM), X-ray diffraction (XRD), scanning electron microscope (SEM), and energy disperse spectroscopy (EDS). The experimental results showed that the α-Al and eutectic Si crystals were modified with the addition of 0.3 wt% La. The eutectic Si crystals showed a granular distribution. At the same time, the alloy possessed the best mechanical property. When more than 0.3 wt% La was added to ADC12 aluminum alloy, the microstructure of as-cast alloy was coarsening gradually with the increase of the content of La and the mechanical property decreased. The effect of rare earth La which was added in ADC12 Al-Alloy for up to 0.9 wt% had been investigated in this study. The dendrites of ADC12 Al-alloy was refined obviously and the morphology of Si crystals showed a particle structure when the addition of La reached 0.3 wt%. Besides, the acicular La-rich intermetallics in the alloy deteriorated the mechanical property of alloy. To avoid this unwanted phase, the amount of added rare earth La must be less than 0.6 wt%.

The Effect of Sn on Microstructure and Mechanical Properties of Mg-Li-Zn-Sn Alloys

The microstructure and tensile properties of the as-cast and as-extruded Mg-12Li-1Zn-xSn (x=1, 3, 5, 8, wt.%) alloys were investigated. The alloys are mainly composed of β-Li phase, Mg2Sn phase. With the increase of Sn content, the microstructure of as-cast alloys is refined. After extrusion processing, grain size is obviously refined, and the Mg2Sn phase is broken into tiny particles. The elevated-temperature tensile behavior of the alloy was investigated at 373~523k under the strain rate of 1×10-2~1.7×10-4s-1. The results indicate addition of Sn can improve the strength and plasticity, when the content of Sn is 5.0 wt.%, the as-extruded alloy possesses good superplasticity, which obtains the maximum elongation of 134.4% under a low strain rate of 1.0×10-3s-1at 523K.

Effect of Process on Microstructure and Elevated Temperature Mechanical Behavior of Multi-Phase NiAl-Fe(Nb) Alloy

The microstructure and elevated temperature mechanical behavior of as-cast, HIPed and directionally solidified NiAl-Fe(Nb) Alloys have been investigated. The results show that the microstructure of as-cast NiAl-Fe(Nb) alloy consists of dendritic regions (b) and interdendritic regions (g/g¢) with non-continuous NbNiAl(Laves) phase segregating at the interfaces of b and g/g¢ phases. The HIP processing does not alter the microstructure of as-cast alloy. The longitudinal dendritic microstructure of the DS NiAl-Fe(Nb) alloy is regular. Room temperature elongations of as-cast and HIPed NiAl-Fe(Nb) alloys are all zero, however, 0.4% for the DS alloy. The strength and elongation of the HIPed alloy are higher than that of as-cast alloy. The yield strength and ultimate strength of the DS alloy are equivalent to that of as-cast alloy, but elongation of the DS alloy is higher than that of as-cast alloy, the elongation exceed 100% at 1273K, which indicates that the DS alloy can be deformed superplastically.

Microstructural and magnetic characterization of iron precipitation in Ni–Fe–Al alloys

The influence of annealing on the microstructural evolution and magnetic properties of Ni{sub 50}Fe{sub x}Al{sub 50-x} alloys for x = 20, 25, and 30 has been investigated. Solidification microstructures of as-cast alloys reveal coarse grains of a single B2 type {beta}-phase and typical off eutectic microstructure consisting of proeutectic B2 type {beta} dendrites and interdendritic eutectic for x = 20 and x > 20 at.% Fe respectively. However, annealing at 1073 K results in the formation of FCC {gamma}-phase particles along the grain boundaries as well as grain interior in x = 20 at.% Fe alloy. The volume fraction of interdentritic eutectic regions tend to decrease and their morphologies start to degenerate by forming FCC {gamma}-phase for x > 20 at.% Fe alloys with increasing annealing temperatures. Increasing Fe content of alloys induce an enhancement in magnetization and a rise in the Curie transition temperature (T{sub C}). Temperature scan magnetic measurements and transmission electron microscopy reveal that a transient rise in the magnetization at temperatures well above the T{sub C} of the alloys would be attributed to the precipitation of a nano-scale ferromagnetic BCC {alpha}-Fe phase. Retained magnetization above the Curie transition temperature of alloy matrix, together with enhanced roommore » temperature saturation magnetization of alloys annealed at favorable temperatures support the presence of ferromagnetic precipitates. These nano-scale precipitates are shown to induce significant precipitation hardening of the {beta}-phase in conjunction with enhanced room temperature saturation magnetization in particular when an annealing temperature of 673 K is used. - Research Highlights: {yields} Evolution of microstructure and magnetic properties with varying Fe content. {yields} Transient rise in magnetization via the formation of ferromagnetic phase. {yields} Enhancements in saturation magnetization owing to precipitated ferromagnetic phase. {yields} Nanoscale precipitation of ferromagnetic BCC {alpha}-Fe confirmed by TEM. {yields} Hardness of the {beta}-phase correlates with room temperature saturation magnetization.« less

Phase relationships in the Al-rich region of the Al–Cu–Er system

The Al-rich region of the ternary Al–Cu–Er system is investigated using the method of X-ray diffraction, scanning electron microscopy with energy dispersive X-ray spectroscopy. Phase equilibria in the Al-rich region of the Al–Cu–Er system at 673K have been obtained, and the microstructures of as-cast alloys in the Al-rich region are also investigated. One ternary phase τ1-Al8Cu4Er with a composition of 59.4–60.4at.% Al, 32.2–33.8at.% Cu, and 6.4–7.7at.% Er is observed in both as-cast and annealed alloys. At 673K, the binary Al3Er phase dissolves about 3.51at.% Cu. The calculated solidification paths (based on the CALPHAD method) of as-cast alloys are in agreement with the experimental results.

The Sequence of Intermetallics Formation during the Solidification of an Al-Mg-Si Alloy Containing La

A mechanism by which La modifies the Fe-bearing intermetallics in a 6xxx series Al alloy is examined using calorimetry. Thermal events accompanying the formation of various phases are identified by establishing a correspondence between them and microstructures of as-cast alloys. It is concluded that a previously suggested surface adsorption mechanism is unlikely to be operative. During solidification, the addition of lanthanum results in the formation of the La(Al,Si)2 phase and the depletion of the remaining melt of Si. It is hypothesized that the decreased Si/Fe ratio in the melt caused by the presence of La favors the formation of the α-AlFeSi phase, which is less detrimental to the formability of the alloy than the β-AlFeSi phase.

Effects of antimony addition on the microstructures of ZA84 magnesium alloy

The effects of antimony (Sb) on the microstructures of as-cast Mg–8Zn–4Al (ZA84) magnesium alloy were investigated by using optical microscopy, SEM, EDX, and XRD, etc. The results indicated that the microstructures of as-cast alloys containing Sb consisted of solid solution α(Mg), ternary phases τ [Mg 32(Al, Zn) 49] and φ (Al 2Mg 5Zn 2), eutectic mixture phase [α(Mg) + τ], a newly formed dual phase MgZn 2, and a newly formed needle-like phase Mg 3Sb 2. After adding Sb, the morphologies of ternary phase on the grain boundaries have been changed from quasi-continuous-net shape to uniformly dispersed particles, and the sizes of grains were decreased from 120–130 μm to 50–60 μm. In this experiment conditions, the optimal addition amount of Sb was 0.3 wt%. Meanwhile, the microhardness of the matrix of ZA84 magnesium alloy was found to increase with the increases of Sb additions. As the phase Mg 3Sb 2 with high melting point and the dual phase MgZn 2 were formed, the high-temperature strength of ZA84 magnesium alloy was increased.

Cooling rate and carbon content effect on the fraction of secondary phases precipitate in as-cast microstructure of ASTM F75 alloy

Simple test castings were used to study the effect of cooling rate and carbon content in as-cast microstructure of alloy ASTM F75, Co–26 wt.% Cr–5.7 wt.% Mo. Alloys with four C content (0.45, 0.33, 0.36 and 0.25 wt.%) were poured into investment ceramic molds. In order to obtain different cooling rates, the castings were constituted of three axisymmetrical cylinders of different diameters (12, 16 and 24 mm). Cooling curves were obtained from each cylinder and the fraction of secondary phases in as-cast microstructure was measured by image analysis. Average cooling rates of 100, 60 and 20 °C/min, were obtained in the 12, 16 and 24 mm diameter cylinders respectively, at the first solidification step occurring in the temperature range from 1390 to 1350 °C. A significant effect of this cooling rate range on the fraction of secondary phase was not observed. It was observed that the fraction of blocky carbides increased proportionally as the C content increased, whereas the amount of the eutectoid constituent showed a significant increase only in the sample containing 0.45 wt.%, as compared with the samples of other carbon contents. It was also found that the initial solidification undercooling affects the temperature of sigma phase precipitation with which the solidification of the alloy is completed.

Microstructures and mechanical properties of double hot-extruded AZ80+xSr wrought alloys

The effects of Sr addition on microstructures and tensile properties of the as-cast and hot-extruded AZ80 alloys were studied by OM, SEM, EDS, XRD, DSC and Instron tester. The results show that the microstructures of as-cast alloys consist of α-Mg and β-Mg17Al12 phase. Sr gathers on the boundaries, and dissolves into β-Mg17Al12 phase or forms Mg17Sr2 phase. The grains of as-cast alloys are refined and discontinuous net-shaped structure is formed. The compound phases on the boundaries become thicker with increasing Sr content. The ultimate tensile stress(UTS) and elongation are improved compared with the corresponding Sr-free alloy. After preliminary hot-extruding, the UTS is up to 308–320 MPa and elongation reaches 8.0%-13.5%. After double hot-extrusion, the dynamic recrystallization completes totally, and the UTS is up to 310–355 MPa, but the elongation does not change apparently. The alloy with 0.02%Sr (mass fraction) obtains the best comprehensive performance with the UTS of 355 MPa and elongation of 13.2%. The SEM morphology of fracture surface shows that the alloys with Sr present good ductility after double hot-extrusion.

Phase Equilibria in Ir‐Rich Portion of Ir—Al—X (X: V, Nb and Ta) Ternary Systems.

Abstract Isotherms of the Ir-rich portion of the Ir–Al–X (X: V, Nb, Ta) systems composed of fcc-Ir solid solution ((Ir) ss ), Ir-based L1 2 intermetallic compounds Ir 3 X and B2–IrAl are presented as a second report of a series of investigations on the phase equilibria in the (Ir or Rh)–Al–X (X: Ti, Zr and Hf, or, V, Nb and Ta) ternary systems. In both Ir–Al–Nb and Ir–Al–Ta systems fcc/L1 2 /B2 three-phase equilibrium is found. In Ir–Al–V system, Ir solid solution and Ir 3 V have close compositions each other and fcc/L1 2 /B2 three-phase equilibrium is expected. No ternary compound is observed in all of the isotherms. Solid solubility of each phase is confirmed by chemical analysis by wavelength dispersive X-ray spectroscopy (WDS). The direction of the solubility lobe of L1 2 –Ir 3 X with Al addition is explained in terms of the nearest neighbor interactions. Liquidus surfaces are also established by taking into account the microstructure of as-cast alloys, differential thermal analysis (DTA) data, and the Ir–Al and the Ir–X binary phase diagrams reported previously.

Phase Equilibria in the Ir‐Rich Portion of the Ir—Al—X (X: Ti, Zr and Hf) Ternary Systems.

Abstract Isotherms of the Ir-rich portion of the Ir–Al–X (X: Ti, Zr, Hf) systems are presented. In all of the isotherms three-phase equilibrium is found and no ternary compound is observed. Solid solubility of each phase is confirmed by chemical analysis by wavelength dispersive X-ray spectroscopy (WDS). The direction of the solubility lobe of L12–Ir3X with Al addition is explained in terms of the nearest neighbor interactions. Liquidus surfaces are also established by taking into account the microstructure of as-cast alloys, differential thermal analysis (DTA) data, Ir–X binary phase diagrams reported previously and the phase equilibria of the Ir–Al binary system investigated in the present study.

Phase equilibria in Ir-rich portion of Ir–Al–X (X: V, Nb and Ta) ternary systems

Isotherms of the Ir-rich portion of the Ir–Al–X (X: V, Nb, Ta) systems composed of fcc-Ir solid solution ((Ir) ss), Ir-based L1 2 intermetallic compounds Ir 3X and B2–IrAl are presented as a second report of a series of investigations on the phase equilibria in the (Ir or Rh)–Al–X (X: Ti, Zr and Hf, or, V, Nb and Ta) ternary systems. In both Ir–Al–Nb and Ir–Al–Ta systems fcc/L1 2/B2 three-phase equilibrium is found. In Ir–Al–V system, Ir solid solution and Ir 3V have close compositions each other and fcc/L1 2/B2 three-phase equilibrium is expected. No ternary compound is observed in all of the isotherms. Solid solubility of each phase is confirmed by chemical analysis by wavelength dispersive X-ray spectroscopy (WDS). The direction of the solubility lobe of L1 2–Ir 3X with Al addition is explained in terms of the nearest neighbor interactions. Liquidus surfaces are also established by taking into account the microstructure of as-cast alloys, differential thermal analysis (DTA) data, and the Ir–Al and the Ir–X binary phase diagrams reported previously.

Phase equilibria in the Ir-rich portion of the Ir–Al–X (X: Ti, Zr and Hf) ternary systems

Isotherms of the Ir-rich portion of the Ir–Al–X (X: Ti, Zr, Hf) systems are presented. In all of the isotherms three-phase equilibrium is found and no ternary compound is observed. Solid solubility of each phase is confirmed by chemical analysis by wavelength dispersive X-ray spectroscopy (WDS). The direction of the solubility lobe of L1 2–Ir 3X with Al addition is explained in terms of the nearest neighbor interactions. Liquidus surfaces are also established by taking into account the microstructure of as-cast alloys, differential thermal analysis (DTA) data, Ir–X binary phase diagrams reported previously and the phase equilibria of the Ir–Al binary system investigated in the present study.

Effect of heat treatment on the microstructure and electrochemical properties of AB 5-type MlNi 3.60Co 0.85Mn 0.40Al 0.15 hydride alloy: 1.—The microstructure and P-C isotherms

In this paper, the microstructure and P-C isotherms of AB 5-type MlNi 3.60Co 0.85Mn 0.40Al 0.15 hydride alloy, heat treated at a temperature of 1373 K , with the holding time 2– 8 h and subsequently water quenched, have been investigated in detail. XRD results showed that the phase structure of all the samples investigated was CaCu 5-type hexagonal structure, whereas the lattice parameters and the FWHM of the alloy were modified by heat treatment. The metallographic microstructure of as-cast alloy was a typical dendritic structure with a number of microcracks at the limb part. After the alloy was heat treated, the microstructure of the alloy was a columnar structure. With the increase in holding time, the grain size increased, the number of the composition segregation dots distributed in the inside of the grain decreased and the width of the grain boundaries broadened. Compared with the P-C isotherms of as-cast alloy, after the alloy is heat treated, the plateau flattened, the plateau pressure decreased and the hysteresis lessened.

Solidification of aluminium alloys under ultrasonic irradiation using water-cooled resonator

The present investigation attempts to evaluate the effect of ultrasonic treatment using water-cooled resonator on the microstructure and properties of different commercial Al-based alloys. The effect of ultrasonic treatment on the as-cast alloy microstructure can be summarized as follows: reduction of mean grain size, variation of phase distribution and better material homogeneity and segregation control. Ultrasonically treated samples have elongation values much higher than those obtainable with control processes. Our investigations confirm great advantages of ultrasonically treated ingots of hypereutectic Al–Si alloys upon deformation in semisolid state.