Microstructure Of Cast Alloy Research Articles

Performance evaluation of developing electrical discharge machining tools through 3D-printed mould using selective laser sintering and expanding its applications in developing free-form tools

In the current study, an attempt has been made to find the optimum parameters for electroplating three-dimensional (3D) casted low melting point alloys. The electroplated profile is used as a tool in an electric discharge machining setup. A selective laser sintering process is used for 3D printing the mould in two halves. The mould parts are 3D scanned to find out the dimensional deviation. The low melting point alloy (LMPA) is cast in the mould. The surface roughness of the mould and the pattern are measured. Electroplating the casted LMPA sample is carried out in three stages in search of optimum parameters for getting stable copper deposits. The thickness of copper deposits under varying conditions is measured. The microstructures of cast alloys and copper deposits are analysed using a scanning electron microscope. The casted alloy and copper composition is verified through energy dispersive spectroscopy mapping and X-ray diffraction technique. The developed electric discharge machining electrode successfully performs the machining on the workpiece, and its performance is compared with that of a solid copper tool. The information gained is transferred to prepare the free-form tool using the developed path and is tested on the implant-shaped workpiece.

Solutions of the scientific problem of modifying of foundry alloys

For a solution of the problem of modification of a microstructure of cast alloys it is necessary to accept admission that crystallization centers of crystals of phases are the crystalline buildups consisting of nanocrystals of phases. The role of modifiers comes down to lower concentration in a metal melt of the dissolved surface-active elements and gases and (or) to formate of the moistened substrates on which process of gas generation and deleting gas bubbles will be most preferable.

Influence of micro-alloying with silver on microstructure and mechanical properties of Al-Cu alloy

The present study aims to investigate the microstructure and mechanical properties of Al-Cu-Zn-Fe-Ti-Mg alloy (≈ 2219 Al-alloy), micro-alloyed with silver (Ag in the range 0 − 0.1 wt%), under different thermo-mechanical process conditions. Investigation of the microstructure of cast alloys revealed the presence of intermetallic CuAl2 and metastable Al-Cu-Fe-Zn-Si-Mn phases at the grain boundary regions. The as-cast dendritic structure was eliminated by heat treatment and subsequent rolling process resulting in improved mechanical properties. The strength and hardness increased with the increase in silver content up to 0.07 wt% in combination with reasonable ductility. Maximum strength for the alloy was achieved in the rolled and age hardened condition. Fractographic studies revealed brittle failure in as-cast alloys, whereas the heat treated alloys exhibited features typical of ductile failure.

Experimental and Stochastic Modeling of the Globular Microstructure and the Microsegregation Evolution during the Solidification of Magnesium Alloys Cast at Low Superheat via Containerless Melting

AbstractCasting at low superheat has a strong influence on the solidification morphology and macro- and microstructures of cast alloys. This paper shows the microstructure and microsegregation of cast Mg AZ31B alloy at superheat of 5°C, summarizes the multiscale model, and describes the simulation results obtained with a previously developed stochastic mesoscopic solidification model capable of predicting the microstructure of the cast alloy. The simulation results are compared with casting experiments carried out using the Magnetic Suspension Melting process. Casting at this low superheat was found to produce castings with a fine globular grain structure, with an average grain size of about 80 µm, which is about one-third the size of that obtained by conventional casting techniques. The stochastic model was validated against the experimental measured grain structure and Al microsegregation. A parametric study was performed to determine some key material and process parameters related to processing of cast Mg AZ31B alloy.

Surface Modification of Cast Al-17%Si Alloys Using Friction Stir Processing

The scope of this investigation is to evaluate the effect of input process parameters of friction stir processing to enhance the mechanical and tribological performance of the cast hypereutectic Al-17%Si alloy. Towards this end, the workpiece material of Al-17% Si alloy was cast to friction stir processing and the effect of process parameter such as tool transverse speed (26, 40, and 60) mm/min, at fixed tool rotational speed 664rpm on the surface characteristics of the cast Al-Si alloy was studied. The results were compiled by using optical microscope, FESEM, hardness, tensile and EDX analysis. The results shows at the optimal input conditions of friction stir processing, the microstructure of cast alloy has been improved in terms of refinement of eutectic and primary Si particles, uniform distribution of Si and the reduction in porosity. In addition, the hardness and tensile properties were improved, the tensile elongation has been increased from < 2% to about 9%.

Microstructure and Hardness of High Temperature Alloy Ti-1100 Melted in CaO Crucible

A high temperature alloy Ti-1100 was produced by vacuum induction melting technology. The effects of casting modulus on the microstructure and hardness of the cast alloys were determined and the results were presented and briefly discussed. Results demonstrate that the microstructure of cast alloys with different modulus are all widmanstatten structure with basket weave features where individual α-laths are separated by a thin layer of retained prior β phase. The greater the modulus, the larger the prior β grain size and α-laths spacing, and the less the Vickers hardness. The roles of the casting modulus governing the microstructures and hardness of the alloys were also discussed.

Experimental and thermodynamic assessment of the Nd–Zr system

The phase equilibria of the binary Nd–Zr system have been investigated by combining the gas levitation technique with in situ high energy synchrotron X-ray diffraction at elevated temperatures. The Nd–Zr system is of a eutectic type. From the diffraction data the liquidus line was experimentally determined between 1300 and 1800K. At T=1274±10K the eutectic reaction L↔ bcc-Nd+bcc-Zr is evident. The eutectic composition x=7±2at% Zr is determined from the analysis of the microstructure of cast alloys in accordance with the in situ diffraction data. Based on the experimental data the Nd–Zr phase diagram is presented and a self-consistent thermodynamic description is given.

Experimental and thermodynamic assessment of the Gd–Zr system

The phase equilibria of the binary Gd–Zr system have been investigated by combining electrostatic levitation of the melt with in situ high energy synchrotron X-ray diffraction. The liquidus line was experimentally assessed between 1500 and 1800K from the diffraction data. At T=1495±10K the eutectic reaction L↔bcc-Gd+bcc-Zr is evident. The eutectic composition x=18±2at% Zr is determined from the in situ diffraction data and confirmed by the analysis of the microstructure of cast alloys. The so far unknown coexistence of bcc-Gd and bcc-Zr is observed for the temperature range 1450K<T<1495K. Based on the experimental data an improved Gd–Zr phase diagram is derived and a thermodynamic description of the binary system is presented.

The effect of solution heat treatments on the microstructure and hardness of ZK60 magnesium alloys prepared under low-frequency alternating magnetic fields

The solidified structure of ZK60 magnesium alloys in the presence and absence of electromagnetic stirring during the solidification process was compared, and the precipitates of ZK60 magnesium alloys were analyzed after a solution heat treatment using optical microscopy, micro-hardness analysis, X-ray diffraction and scanning electron microscopy. The results showed that the microstructure of cast alloys under a low-frequency alternating magnetic field (LFAMF) was mainly composed of a primary crystalline Mg matrix and a non-equilibrium eutectic structure (Mg+MgZn+MgZn2). In comparison with the microstructure observed in the absence of the electromagnetic field, the eutectic network structure on the grain boundary under low-frequency alternating magnetic field was finer and exhibited a more uniform grain distribution. The grains under the LFAMF were refined in comparison with those under no electromagnetic field before the solution heat treatment, and the former grain distribution was more uniform than the latter after the solution heat treatment. The more uniform grain distribution is because the solution heat treatment is conducive to the dissolution of the second phase particles. The hardness exhibited a downward trend with increasing solution heat treatment time. Under the same solution heat treatment, the hardness value of the samples prepared under the LFAMF was lower than those prepared in the absence of the electromagnetic field. In contrast, the mechanical properties of alloys prepared under the LFAMF were better than those prepared in the absence of the electromagnetic field.

ChemInform Abstract: Structural and Magnetic Properties of Nd17Fe76(B1-xCx)7 Alloys

The influence of partial C substitution for B on structural and magnetic properties of Nd17Fe76(B(1-x)C(x))7 alloys has been studied. It has been discovered that the stable hard magnetic phase Nd2Fe14(B,C) with the tetragonal structure can be formed if x < 0.9. As the C content increases, the lattice constant a is nearly constant whereas c decreases linearly. Furthermore, with increasing C content , the microstructure of cast alloys and sintered magnets varies. The temperature dependence of the anisotropy field H(A) and the coercivity i(H)c of the Nd17Fe76(B(1-x)C(x)7 alloys was measured from room temperature up to about 300-degrees-C. The anisotropy field H(A) increases whereas the coercivity i(H)c decreases greatly with increasing C content.

Microstructure evolution of semi-solid Mg-14Al-0.5Mn alloys during isothermal heat treatment

A new Mg-14Al-0.5Mn alloy that exhibits a wide solidification range and sufficient fluidity for semi-solid forming was designed. And the microstructure evolution of semi-solid Mg-14Al-0.5Mn alloy during isothermal heat treatment was investigated. The mechanism of the microstructure evolution and the processing conditions for isothermal heat treatment were also discussed. The results show that the microstructures of cast alloys consist of α-Mg, β-Mg 17Al 12 and a small amount of Al-Mn compounds. After holding at 520 °C for 3 min, the phases of β-Mg 17Al 12 and eutectic mixtures in the Mg-14Al-0.5Mn alloy melt and the microstructures of α-Mg change from developed dendrites to irregular solid particles. With increasing the isothermal time, the amount of liquid increases, and the solid particles grow large and become spherical. When the holding time lasts for 20 min or even longer, the solid and liquid phases achieve a state of dynamic equilibrium.

Deformation behavior of commercial Mg-Al-Zn-Mn type alloys under a hydrostatic extrusion process at elevated temperatures

This paper presents the deformation behavior of commercial Mg-Al-Zn-Mn type alloys during hydrostatic extrusion process at elevated temperatures. In the current study commercial Mg-Al-Zn-Mn type alloys with different Al contents were subjected to hydrostatic extrusion process at a range of temperatures and at ram speeds of 4.5, 10 and 17 mm/sec. Under the hydrostatic condition at 518K, the alloy with Al contents of 2.9 wt% was successfully extruded at all applied speeds. The alloys with Al content of 5.89 and 7.86 wt% were successful up to 10mm/sec, and finally extrusion of alloy with Al content 8.46wt% was successful only at 4.5 mm/sec. These results show that the deformation limit in the Mg alloys in terms of extrusion speed greatly extended to higher value in the proximity of lower Al content. It is presumed that deformation becomes harder as Al content increases because of strengthening mechanism by solute drag to increase of supersaturated Mg17 Al12 precipitates. Also, microstructures of cast and extruded Mg alloys were compared. Defect-wide microstructure of cast alloy completely evolved into dense and homogeneous microstructure with equiaxed grains.

The Influence of Fluid Flow on the Microstructure of Directionally Solidified AlSi-Base Alloys

To obtain a quantitative understanding of the effect of fluid flow on the microstructure of cast alloys, a technical Al-7 wt pct Si-0.6 wt pct Mg alloy (A357) has been directionally solidified with a medium temperature gradient under well-defined thermal and fluid-flow conditions. The solidification was studied in an aerogel-based furnace, which established flat isotherms and allowed the direct optical observation of the solidification process. A coil system around the sample induces a homogeneous rotating magnetic field (RMF) and, hence, a well-defined flow field close to the growing solid-liquid interface. The application of RMFs during directional solidification results in pronounced segregation effects: a change to pure eutectic solidification at the axis of the sample at high magnetic field strengths is observed. The investigations show that with increasing magnetic induction and, therefore, fluid flow, the primary dendrite spacing decreases, whereas the secondary dendrite arm spacing increases. An apparent flow effect on the eutectic spacing is observed.

A Combined Numerical and Experimental Study of the Effects of Controlled Fluid Flow on Alloy Solidification

A quantitative understanding of the effect of fluid flow on the microstructure of cast alloys is still lacking. The application of time dependent magnetic fields during solidification offers the possibility to create defined flow conditions in solidification processing. The effect of rotating magnetic fields (RMF) on the microstructure formation in cast Al-alloys (Al-7wt.%Si, Al-7wt.%Si- 0.6wt.Mg) is studied experimentally and numerically. The forced fluid flow conditions result in pronounced macrosegregation effects and affect microstructural parameters. With increasing fluid flow the primary dendrite spacing decreases whereas the secondary dendrite arm spacing increases. The experimental analysis is supported by a rigorous application of numerical modeling with the software package CrysVUn.

Processing and mechanical properties of a molybdenum silicide with the composition Mo–12Si–8.5B (at.%)

Alloys with the nominal composition Mo–12Si–8.5B (at.%) were prepared by arc-melting or powder-metallurgical processing. Cast and annealed alloys consisted of approximately 38 vol.% α-Mo in a brittle matrix of 32 vol.% Mo 3Si and 30 vol.% Mo 5SiB 2. Their flexure strengths were approximately 500 MPa at room temperature, and 400–500 MPa at 1200°C in air. The fracture toughness values determined from the three-point fracture of chevron-notched specimens were about 10 MPa m 1/2 at room temperature and 20 MPa m 1/2 at 1200°C in air. The relatively high room temperature toughness is consistent with the deformation of the α-Mo particles observed on fracture surfaces. Three-point flexure tests at 1200°C in air and a tensile test at 1520°C in nitrogen indicated a small amount of high temperature plasticity. Extrusion experiments to modify the microstructure of cast alloys were unsuccessful due to extensive cracking. However, using powder-metallurgical (PM) techniques, microstructures consisting of Mo 3Si and Mo 5SiB 2 particles in a continuous α-Mo matrix were fabricated. The room temperature fracture toughnesss of the PM materials was on the order of 15 MPa m 1/2.

Microstructural control of NdFeB cast ingots for achieving 50 MGOe sintered magnets

The combination of chemical composition and microstructure of cast alloy has been found to be critical to the performance of NdFeB sintered magnets. Maximizing the amount of Nd2Fe14B phase (or minimizing the amount of secondary phase) by reducing the Nd content more closely to the stoichiometric composition appears to be essential for obtaining high BHmax magnets. However, α-Fe precipitation has been found to increase with decreasing Nd content and severely hinders the development of high BHmax magnets. A two-step method, incorporating ingot casting and isothermal annealing, has been developed to minimize the amount of precipitated α-Fe in low Nd content alloys. This method provides a drastic improvement in the Br and BHmax of sintered magnets obtained. By decreasing the Nd content to 13 at. % in the cast alloy, incorporating better particle control during fine milling, and controlling grain growth during sintering; magnets with a Br of more than 14.5 kG and a BHmax of 50 MGOe have been consistently obtained. Furthermore, because of the reduction in the amount of Nd-rich grain boundary phase, a significant improvement in the corrosion resistance of magnets was also observed.

Magnetic Properties of Anisotropic Pr-Fe-B Melt-Spun Ribbons

The magnetic properties and microstructure of Pr-Fe-B(Ga) melt-spun ribbons prepared by the single- or twin-roller method were studied. A texture with the c-axis normal to the surface was observed in slowly quenched ribbons, and showed a strong dependence on composition. Addition of Ga is effective for increasing the coercivity and the c-axis alignment of ribbons. Magnetic measurements of powders obtained by crushing ribbon samples prepared by the twin-roller method revealed that the powders solidified in a paraffin bath with a magnetic field of 12 kOe applied had a high coercivity of iH c =13.8 kOe and a higher remanence than did powders solidified without a field applied. Observations of the microstructure of cast alloys suggest that the strong c-axis alignment arises from the rapid quenching.

Structural and magnetic properties of Nd 17Fe 76(B 1− xC x) 7 alloys

The influence of partial C substitution for B on structural and magnetic properties of Nd 17Fe 76(B 1 − x C x ) 7 alloys has been studied. It has been discovered that the stable hard magnetic phase Nd 2Fe 14(B,C) with the tetragonal structure can be formed if x < 0.9. As the C content increases, the lattice constant a is nearly constant whereas c decreases linearly. Furthermore, with increasing C content, the microstructure of cast alloys and sintered magnets varies. The temperature dependence of the anisotropy field H A and the coercivity i H c of the Nd 17Fe 76 (B 1 − x C x ) 7 alloys was measured from room temperature up to about 300 °C. The anisotropy field H A increases whereas the coercivity i H c decreases greatly with increasing C content.

Microstructural changes during annealing of cast Ni–Cr–Hf alloys

Abstract In order to gain knowledge of the nickel–rich corner of the Ni–Cr–Hf phase diagram, microstructures of cast alloys and their evolution towards equilibrium conditions have been followed by optical and scanning electron microscopy, microprobe analysis, and quantitative metallography. The evolution of as–cast microstructures involves the development of a Ni5Hf plate–like precipitate in two–phase alloys, and various morphological changes in three–phase alloys. As–cast structures are compared with those obtained by arc melting. Direct processing of the scanning electron microscope image has proved to be a valuable tool for microstructural characterization of the transforming phases.MST/349