Molten Aluminum Alloy Research Articles

The Effect of Production Process Parameters on the Tensile Strength of Squeeze Cast Al2O3+SiC/Al6061 Hybrid Composites

Abstract This study investigated the conditions for the optimal performance of hybrid aluminum matrix composites produced by squeeze casting. The significant die casting parameters chosen for analysis were the squeeze pressure (50, 70, 90 MPa); die preheat temperature (100, 200, 300°C) and duration of pressurization (15, 30, 45 s). Composites containing 10 and 20 % volume fractions of reinforcements were synthesized by infiltrating molten aluminum alloy 6061 into prefabricated porous preforms composed of Al2O3+SiC microparticles. Experiments were conducted by implementing the L933 orthogonal design of Taguchi, where the objective function was to maximize the tensile strength of the castings by appropriate statistical analysis. The results suggested that the production process was successful as the microparticles were evenly distributed within the matrix alloy. The control parameters of squeeze pressure and duration of pressurization were found to be the most significant factors influencing the tensile strength of the castings. As the volume fraction of reinforcements increases in the composites, the duration of pressurization is the most critical factor to enhance the tensile strength. The optimal control settings required to maximize tensile strength were specified with respect to the volume fraction of reinforcements content. The data from statistical experimental design was compared with mathematical predictions and through verification tests, these results were found to be in close agreement.

Improving the Corrosion Resistance of Hot-Working Mold Steel against Al Alloy Melt by Coating

In order to reduce the adhesion tendency of aluminum melt on the die casting mold and extend the service life of the die, multi-arc ion plating technique was used to deposit Ti/TiN/CrN multi-layer coating on the surface of 8418 hot-working mold steel. Corrosion resistance of the steel and the Ti/TiN/CrN coating against Al alloy melt was studied. X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy were used to study the microstructure, phase constituent and phase composition of the materials. Uniform Ti/TiN/CrN coatings with good bonding interfaces and a total thickness of about 2 μm were obtained. Results showed that Ti/TiN/CrN coating can improve the corrosion resistance of the 8418 hot-working die steel significantly against the aluminum alloy melt.

Formation of different alumina phases and magnesium aluminate spinel during contact of molten AlSi7Mg0.6 alloy with mullite and amorphous silica

Corrosion of alumina-based metal melt filters functionalized by 3Al2O3·2SiO2 or fused SiO2 was investigated using local chemical and microstructure analyses and thermodynamic calculations. Molten aluminium alloy AlSi7Mg0.6 was employed as corrosion medium. The aluminium alloy was melted in a Spark Plasma Sintering apparatus in order to avoid the melt flow. During the reaction with the AlSi7Mg0.6 melt, 3Al2O3·2SiO2 partly decomposed, and Al2O3 reacted with magnesium from the melt and with oxygen from SiO2 to MgAl2O4. Silicon precipitated in the aluminium alloy. For corundum functionalized by fused SiO2, metastable γ-Al2O3 was detected additionally to the above phases for short reaction times.

The Effect of the Additional Processing during the Crystallization of a Melt of the AD0 Aluminum Alloy on the Size of Grains

During the process of the aluminum ingot manufacturing obtaining of a fine-grained structure has a huge significance for effectiveness of the further rolling process. The reduction of the grain size leads to an increased plasticity and higher grades of deformability. Today the multiple methods of improving the casting process are being developed varying from mechanical to physical or chemical methods, and their choice depends on different factors. However, the effect on the size of grains of the multi-factor impact was not described in literature. This paper investigates methods of casting including piston pressing with simultaneous exposure to the weak pulsed currents from electromagnetic field during crystallization of melted metal for the first time. The fine-grained uniform over the cross-section structure was achieved in the AD0 alloy ingots.

ИЗМЕНЕНИЕ СТРУКТУРЫ СПЛАВА АК9ч., ПОЛУЧЕННОГО СЕЛЕКТИВНЫМ ЛАЗЕРНЫМ СПЕКАНИЕМ, В ПРОЦЕССЕ ТЕРМИЧЕСКОЙ ОБРАБОТКИ

ИЗМЕНЕНИЕ СТРУКТУРЫ СПЛАВА АК9ч., ПОЛУЧЕННОГО СЕЛЕКТИВНЫМ ЛАЗЕРНЫМ СПЕКАНИЕМ, В ПРОЦЕССЕ ТЕРМИЧЕСКОЙ ОБРАБОТКИ

Synthesis of Aluminum-Aluminum Nitride Nanocomposites by Gas-Liquid Reactions I. Thermodynamic and Kinetic Considerations

In-situ fabrication of the reinforcing particles directly in the metal matrix is an answer to many of the challenges encountered in manufacturing metal matrix nanocomposite materials. In this method, the nanosized particles are formed directly within the melt by means of a chemical reaction between a specially designed metallic alloy and a reactive gas. The thermodynamic and kinetic characteristics of this chemical reaction dictate the particle size and distribution in the matrix alloy, as well as the nature of the particle/matrix interface, and consequently, they govern many of the material’s mechanical and physical properties. This article focuses on aluminum-aluminum-nitride nanocomposite materials that are synthesized by injecting a nitrogen-bearing gas into a molten aluminum alloy. The thermodynamic and kinetic aspects of the process are modeled, and the detrimental role of oxygen is elucidated.

Use of Thermodynamic Modeling for Selection of Electrolyte for Electrorefining of Magnesium from Aluminum Alloy Melts

With United States Department of Energy Advanced Research Project Agency funding, experimental proof-of-concept was demonstrated for RE-12TM electrorefining process of extraction of desired amount of Mg from recycled scrap secondary Al molten alloys. The key enabling technology for this process was the selection of the suitable electrolyte composition and operating temperature. The selection was made using the FactSage thermodynamic modeling software and the light metal, molten salt, and oxide thermodynamic databases. Modeling allowed prediction of the chemical equilibria, impurity contents in both anode and cathode products, and in the electrolyte. FactSage also provided data on the physical properties of the electrolyte and the molten metal phases including electrical conductivity and density of the molten phases. Further modeling permitted selection of electrode and cell construction materials chemically compatible with the combination of molten metals and the electrolyte.

Thermodynamics and kinetics analyses of ZrB2 formation in molten aluminium alloys

Smelter grade aluminium can be used as a source for electrical conductor grade aluminium after the transition metal impurities such as zirconium (Zr), vanadium (V), titanium (Ti) and chromium (Cr) have been removed. Zirconium (Zr), in particular, has a significant effect on the electrical conductivity of aluminium. In practice, the transition metal impurities are removed by adding boron-containing substances into the melt in the casthouse. This step is called boron treatment. The work presented in this paper, which focuses on the thermodynamics and kinetics of Zr removal from molten Al–1 wt-%Zr–0.23 wt-%B alloy, is part of a broader systematic study on the removal of V, Ti, Cr and Zr from Al melt through boron treatment carried out by the authors. The thermodynamic analyses of Zr removal through the formation of ZrB2 were carried out in the temperature range of 675–900°C using the thermochemical package FactSage. It was predicted that ZrB2 is stable compared to Al–borides (AlB12, AlB2) hence would form during boron treatment of molten Al–Zr–B alloys. Al–Zr–B alloys were reacted at 750 ± 10°C for 60 minutes, and the change in the chemistry and microstructure were tracked and analysed at particular reaction times. The results showed that the reaction between Zr and AlB12/B was fast as revealed by the formation of boride ring at the early minutes of reaction. The presence of black phase (AlB12), i.e. the original source of B, after holding the melt for 60 minutes advocated that the reaction between Zr and AlB12/B was incomplete, hence still not reached the equilibrium state. The kinetics data suggested a higher reaction rate at the early minutes (2 minutes) of reaction compared to at a later stage (2–60 minutes). Nevertheless, a simple single-stage liquid mass transfer controlled kinetic model can be used to describe the overall process kinetic. The analysis of integrated rate law versus reaction time revealed that the mass transfer coefficient (km) of Zr in molten alloy is 9.5 × 10−4 m s−1, which is within a typical range (10−3 to 10−4 m s−1) observed in other metallurgical solid–liquid reactions. This study suggests that the overall kinetics of reaction was predominantly controlled by the mass transfer of Zr through the liquid aluminium phase.

Mold-Filling Ability of Aluminum Alloy Melt during the Two-Step Foaming Process

For the two-step foaming method, one of the most cost-effective ways to fabricate three-dimensional shaped aluminum alloy foams with dense outer surface skin, it is crucial to describe and predict the mold-filling behavior of the shaped aluminum alloy foams with a favorable pore-distribution accurately. In this paper, a mold-filling model for semi-solid aluminum alloy foams was initially established and subsequently employed to predict the filling height, which represents the mold-filling ability of semi-solid aluminum alloy foams in a specially designed tube-like mold. Our results indicate that the proposed model can be applied to characterize the mold-filling property of aluminum alloy melts in a quantitative manner. Theoretically, our findings actually provide a guideline for mass-production of the shaped aluminum alloy foams by using the two-step foaming process.

Numerical study of influence of oblique plate length and cooling rate on solidification and macrosegregation of A356 aluminum alloy melt with experimental comparison

The present study describes about the preparation of semisolid metal (SSM) slurry by using an oblique plate. In this process, A356 aluminum alloy melt partially solidifies while flowing over a bottom cooled oblique plate. Melt flow inertia shears columnar dendrites formed on plate wall into equiaxed/fragmented grains by resulting semisolid slurry at plate exit. Effects of plate length providing required shear and cooling rate enabling necessary solidification are investigated. A 3-phase numerical model vis-à-vis transport of mass, momentum, energy and species is developed for prediction of velocity, temperature, macrosegregation and solid fraction. Model uses volume of fluid (VOF) for tracking-metal-air-interface and finite volume method (FVM) with enthalpy based phase change algorithm for tracking-solid-liquid-interface within the metal. Darcy model is used for porous mushy zone. Slurry variable viscosity is represented by Oldenburg model. Stokes model incorporates solid phase movement and gravity effect along the flow. Dendrite fragmentation is considered for generation of moving solid phase. Solid movement is handled by coherency point and characteristic diameter of moving grains. Model neglects nucleation and growth kinetics, solidification shrinkage/expansion and thermo-solutal buoyancy. Slurry solid fractions at plate exit are 16%, 22%, and 27% for plate lengths of 200 mm, 250 mm, and 300 mm, respectively. And, are 5%, 22%, and 27% for heat transfer coefficients of 1000 W/m2-K, 2000 W/m2-K and 2500 W/m2-K, respectively. Numerical predictions agree well with experimental results.

Superior tensile properties of in situ nano-sized TiCp/Al-Cu composites fabricated by reaction in melt method

The nano-sized TiCp/Al-Cu composites were fabricated using the self-propagating high-temperature synthesis (SHS) reaction of Al-Ti-CNT master alloys in molten aluminum alloys. The tensile strength and ductility of the alloys were simultaneously improved by the addition of nano-sized TiC particles. The yield strength, ultimate tensile strength and fracture strain of the 0.3wt% nano-sized TiC particles reinforced Al-Cu matrix composite increased to 350MPa, 554MPa and 14.75%, improved by 15.5%, 14.2% and 123.5%, respectively, compared with the unreinforced Al-Cu alloy (303MPa, 485MPa and 6.6%). The enhanced mechanical properties are attributed to the refined α-Al dendrites, a larger amount of smaller θ′ precipitates and the dispersed nano-sized TiC particulates. This study provides a feasible method to fabricate the nano-sized TiCp/Al-Cu composites with superior strength and ductility.

Manufacturing of cast A356 matrix composite reinforced with nano- to micrometer-sized SiC particles

In this study, large micron-sized SiC particles were fragmented via ball-milling process in the presence of iron and nickel powders, separately, to fabricate composite powders of Fe–SiC and Ni–SiC. Continuous fracturing of brittle SiC powders leads to the formation of multi-modal-sized SiC powders with size of from 50 nm to slightly higher than 10 µm after 36-h ball milling. The milled powders were then incorporated into the semisolid melt of A356 aluminum alloy to ease the incorporation of fine SiC particles by using iron and nickel as their carrier agents. The final as-cast composites were then extruded at 500 °C with a reduction ratio of 9:1. Lower-sized composite powders with slight agglomeration are obtained for the 36-h milled Ni–SiC mixture compared to that of Fe–SiC powders, leading to incorporation of SiC particles into the melt with a lower size and suitable distribution for the Ni–SiC mixture. It is found that lower-sized composite particles could release the fine SiC particles into the melt more easily, while large agglomerated composite particles almost remain in its initial form, resulting in sites of stress concentration and low-strength aluminum matrix composites. Ultimate tensile strength (UTS) and yield strength (YS) values of 243 and 135 MPa, respectively, are obtained for the aluminum matrix composite in which nickel acts as the carrier of fine ceramic particles.

Fabrication of Al-AlN Nanocomposites

A review of the methods of obtaining and properties of aluminum matrix composites, discretely reinforced with ceramic particles and nanoparticles of aluminum nitride AlN, is given. The survey shows that at low weight, nanocomposites Al-AlN possess improved physical and mechanical properties, including at high temperatures up to 400-550°C, which makes them very attractive for applications in automotive, aerospace and semiconductor technology. However, due to the long duration and energy consumption, expensive and complicated equipment, low productivity of existing solid-phase methods of powder metallurgy and liquid-phase metallurgical processes of fabrication of nanocomposites of Al-AlN, there are not yet the mastered technologies of industrial production of these composites. Azide technology of self-propagating high-temperature synthesis (SHS-AZ) using sodium azide NaN3 as a solid nitriding reagent allows you to get relatively inexpensive nanopowder of aluminum nitride in the form of nanofibers along with side salt of cryolite Na3AlF6, which can play the role of flux when working with molten aluminum. A new simple ex-situ method of introduction of AlN particles in the molten aluminum alloy in the form of a composite master alloy obtained by fusing together a flux carnallite KCl·MgCl2 with AlN nanopowder mixed with cryolite Na3AlF6 was proposed. Results of experiments on the application of the proposed method for obtaining nanocomposite with matrix made of aluminum-magnesium alloy AlMg6 containing up to 1 % of the reinforcing phase AlN are presented.

Transverse cracking in metal/ceramic composites with lamellar microstructure

Metal/ceramic composites with lamellar microstructures are a novel class of metal-matrix composites produced by infiltration of freeze-cast or ice-templated ceramic preforms with molten aluminium alloy. The cost-effectiveness of production and relatively high ceramic content make such composites attractive to a number of potential applications in the automotive, aerospace and biomedical engineering. A hierarchical lamellar microstructure exhibited by these composites, with randomly orientated domains in which all ceramic and metallic lamellae are parallel to each other, is the result of the ice crystal formation during freeze-casting or ice templating of preforms from water-ceramic suspensions. In this paper, a single-domain sample of metal/ceramic composite with lamellar microstructure is modelled theoretically using a combination of analytical and computational means. Stress field in the sample containing multiple transverse cracks in the ceramic layer is determined using a modified 2-D shear lag approach and a finite element method. Degradation of stiffness properties of the sample due to multiple transverse cracking is also predicted.

Microstructure Characteristic of Adiabatic Shear Bands for Aluminum Matrix Composites Compressed With High Strain Rates

In this paper, the novel transformed bands in adiabatic shear bands (ASBs) were researched which was characterized as melting or solid to liquid phase transformation. By split Hopkinson pressure bar (SHPB), optical microscope (OM) and scanning electron microscope (SEM), microstructure characteristic in the transformed bands at varied strain rates were observed. From the experimental results, it was found that molten aluminum bands and aluminum balls agglomeration, which called transformed bands, were found on the shearing surface for 55%TiB2/Al composites compressed at strain rates of 1~2×103 s -1 . It was concluded that there were the molten aluminium alloy and the molten aluminium particles on the shear flat surface oriented at an angle approximately 45°to the compression axis, which was transformed band. It was formed due to aluminium alloy melt at high temperature and solidified sharply by analysis. The formation of transformed bands was ascribed to adiabatic temperature rise, which caused aluminum alloy matrix softened and molten. The adiabatic temperature rise was 800-900K by caculation. The local high temperature led to the formation of the molten aluminium particles whose diameter was 1-3µm on the adiabatic shear flat surface. With the rapid convergence of molten aluminium particles and growing up, the adiabatic shear band was finally formed.

Development of De-phosphorus Treatment Process for Molten Aluminum Alloy

Development of De-phosphorus Treatment Process for Molten Aluminum Alloy

Effect of Coat Permeability on Melt Velocity of Molten Aluminum Alloy in Expendable Pattern Casting Process

Effect of Coat Permeability on Melt Velocity of Molten Aluminum Alloy in Expendable Pattern Casting Process

Effect of Coat Permeability on Melt Velocity of Molten Aluminum Alloy in Expendable Pattern Casting Process

Effect of Coat Permeability on Melt Velocity of Molten Aluminum Alloy in Expendable Pattern Casting Process

Analysis of multiple cracking in metal/ceramic composites with lamellar microstructure

Metal/ceramic composites with lamellar microstructures are a novel class of metal-matrix composites produced by infiltration of freeze-cast or ice-templated ceramic preforms with molten aluminium alloy. The cost-effectiveness of production and relatively high ceramic content make such composites attractive to a number of potential applications in the automotive, aerospace and biomedical engineering. A hierarchical lamellar microstructure exhibited by these composites, with randomly orientated domains in which all ceramic and metallic lamellae are parallel to each other, is the result of the ice crystal formation during freeze-casting or ice-templating of preforms from water–ceramic suspensions. In this paper, a single-domain sample of metal/ceramic composite with lamellar microstructure is modelled theoretically using a combination of analytical and computational means. Stress field in the sample containing multiple transverse cracks in the ceramic layer is determined using a modified 2-D shear lag approach and a finite element method. Using finite element modelling, the shear layer thickness is determined and used as input in the analytical model. Degradation of stiffness properties of the sample due to multiple transverse cracking is predicted using the equivalent constraint model.

Fabrication of PyC/SiC Compound Coating on Carbon Fiber Preform and Its Effect on the Properties of Cf/Al Composite

Abstract PyC/SiC compound coating was deposited on carbon fiber preform by chemical vapor deposition (CVD) process for improving the wettability and reducing the chemical reaction between molten aluminum alloy and carbon fibers. Cf/Al composites were fabricated through the extrusion directly following vacuum pressure infiltration process. Effects of coating deposition parameters on the quality of carbon fiber coating were studied, and the influences of the coating on the infiltration quality and the mechanical properties of composites were also investigated by means of the microstructural analysis and mechanical property tests. The results show that the deposition rate of the coating is mainly controlled by the deposition temperature, and the uniform thickness of PyC/SiC compound coating can be obtained by controlling the deposition temperature or deposition time. The coating on carbon fiber preform can improve the infiltration quality and mechanical properties greatly based on the suitable interface bonding strength and good wettability. The optimized PyC/SiC compound coating thicknesses are 0.068 µm (PyC coating) and 0.257 µm (SiC coating) for better improving the composite properties.