Molten Al Alloy Research Articles

The relationship between thermal decomposition properties of titanium hydride and the Al alloy melt foaming process

Using a new temperature programmed decomposition (TPD) theory and related experimental technique, a set of thermal decomposition kinetics equations of titanium hydride can be acquired by separating and simulating its TPD spectrum. According to these equations, the relation curve of decomposition quantity and time for titanium hydride at temperature of 940 K is obtained and the result coincides well with the Al alloy melt foaming process, which provides a scientific basis for controlling the Al alloy melt foam and then the Al alloy foams with different pore structure are successfully prepared.

Interfacial Reaction between Molten Al Alloys and Titanium Matrix Composites

The aim of this study is to investigate the applicability of titanium matrix composites (TMCs) sleeve to Al alloys die-casting. Ti and 1.88 mass% B4C were prepared for the synthesis of 10 vol% (TiC+TiB) hybrid TMCs. In-situ synthesis and net-shape forming of TMCs were carried out in a vacuum induction melting furnace. The synthesized (TiC+TiB) TMCs were examined using scanning electron microscopy, an electron probe micro-analyzer, X-ray diffraction and transmission electron microscopy. The resistance-ability of (TiC+TiB) TMCs to molten Al alloys attack was also examined. Their reactions were carried out in a furnace at 993 K for times varying from 0 to 1200 s. In the case of conventional sleeve material, H13 steel, there were severe interfacial reactions and erosion after 60 s. On the other hand, the resistance of (TiC+TiB) TMCs to interfacial reactions and erosion by molten A380 alloy was significantly increased.

In-Situ Joining of Combustion Synthesized Ni-Al Alloys with Al Casting Alloy

We focused on the surface reinforcement of Al casting alloys with Ni-Al intermetallic compounds by in-situ combustion reaction to improve the surface properties of Al casting components. Microstructure and phase formation behavior of Ni-Al based intermetallic compounds synthesized by combustion reaction were investigated in terms of thermal and phase analysis using scanning electron microscope(SEM) equipped with energy dispersive x-ray spectrometer (EDS) and x-ray diffractometer(XRD) in Ni-Al intermetallic compounds. Three kinds of nickel aluminides, NiAl3, NiAl and Ni3Al, were synthesized by emission heat from the Al molten metal in order to form a coating layer of intermetallic phase simultaneously on the solidifed Al alloy surface. The synthesized shapes and microstructures of nickel aluminides were varied by casting temperature, Si contents, and the mixing ratio of elemental powders. The synthesized reaction products formed in nickel aluminides were observed to be different depending on the mixing ratio of elemental powders. The reaction layer of about 25m thickness was formed at the interface, and it mainly consisted of NiAl3 phase by the reaction between liquid molten Al alloy and solid Ni powders in green compact. With this information, we successfully produced a coating layer of Ni3Al intermetallic compound onto the casting Al alloy surface using molten metal heat without any additional process. These findings led us to conclude that a near-net shaped nickel aluminide coating layer can be formed using this unique process.

Characteristics of a near-net-shape formed Al–Al 3Fe eco-functionally graded material produced over its eutectic melting temperature

With the concept of an eco-material in mind, this work looks into the possibility of manufacturing Al–Al 3Fe functionally graded material (FGM) products by semi-solid extrusion. For this purpose, an Al–Al 3Fe FGM thick-walled tube of 90 mm outer diameter × 90 mm long × 15 mm thickness was fabricated utilizing a vacuum centrifugal method. Al–Al 3Fe FGM billets of 40 mm diameter × 12 mm thickness, with graded distribution from 0 to 40 vol% of coarse brittle Al 3Fe particles in the thickness direction, were machined from the thick-walled FGM tube. The billets were pressed in the container at temperatures of 660, 670 and 680 °C, where Al alloy melt and solid Al 3Fe particles co-existed. A near-net-shape product of Al–Al 3Fe FGM, in the form of a cup, was successfully fabricated through the semi-solid backward extrusion process during which lower test temperatures produced better results. The volume fraction concentration of Al 3Fe appears to be independent of the test temperature and over 60 vol% around the bottom cup region, decreasing gradually towards the cup wall region. The shape of coarse Al 3Fe particles changes to a more fine fibrous shape at some locations whilst remaining unchanged in others. The shape change mechanism appears not to be due to melt flow erosion, dissolution and/or re-crystallization, but rather due to viscous melt flow splitting of coarse particles. The brittleness of the coarse Al 3Fe intermetallic compound that makes the application of conventional plastic deformation methods impossible appears not to be the case during near-net-shape forming over eutectic melting point. Shore hardness increases with increasing volume fraction of Al 3Fe particles and following semi-solid forming the product appears to be harder than before. This appears to be the result of refining of Al 3Fe particles through shear stress introduced by liquid Al flow during semi-solid forming. Fabrication of FGMs having fine fibrous Al 3Fe phase, appears to be possible if the forming process is carried out at an optimum condition.

Preparation of AlN matrix composites using an infiltration and reaction approach

Aluminum nitride (AlN) matrix composites were prepared by a novel approach. Porous preforms containing Si 3N 4 and Al 2O 3 were fabricated after sintered at 1450 °C in N 2. Then, molten Al–10Si–5Mg alloy was infiltrated into preforms in air at temperature of 850 and 950 °C to form ceramic/metal composites using the pressure less metal infiltration process. Finally, the as-infiltrated composites were heat-treated to over 1200 °C in air in order to form AlN matrix composites. The test results shown that Si 3N 4 had reacted with Al to form AlN when molten Al alloy was infiltrated into the porous preforms at 850 and 950 °C, a large amount of AlN phase in the composite was detected after heat-treated at 1200 and 1300 °C. The composites had higher hardness than that of AlN made by traditional processing. The composite microstructures and its phase makeup were observed and analyzed by SEM, EDS and XRD.

Precipitation of Sr-rich intermetallic particles and their influence on pore formation in Sr-modified A356 alloy

The nature of enhanced pore formation in Sr-modified A356 Al alloy melts has been investigated, leading to the observation of the precipitation of Sr-rich compounds on the wetted side of oxide films. Scanning electron microscopy of casting surfaces showed that the surface oxide film might be a good possible nucleation site of Sr-rich compounds. The observation of internal pores using secondary electron microscopy and X-ray microanalysis mapping showed precipitation of Sr-rich compounds on the wetted side of the oxide films in most pores. The possibility of Sr-rich intermetallics being nucleated on oxide films was assessed by determining their planar disregistry factor; good matching planes were found between Al2Si2Sr intermetallics and γ-Al2O3 and spinel oxide films. The crystallographic alignment revealed in scanning electron microscope (SEM) images also corroborates an epitaxial relationship. Mechanisms by which Sr in Al-Si alloys may contribute to the formation of porosity are discussed.

Significance of gate geometry and injection speed on the flow behaviors of molten Al alloy during die filling

The effects of injection speed and gate geometry on the flow behaviors of molten Al alloy (Newtonian fluid) were investigated by direct observations of the flow patterns during die filling. High-speed photography was employed to record the real time flow patterns of the molten metal during the die filling sequence. Qualitative assessments of the critical gate speed were made based on the experimental results. The experimental results were also compared with results predicted based on the Reynolds number. Although the critical gate speed varies depending on the gate geometry, a gate speed of ≈0.5 m/s is considered optimal to control the flow behavior of the melt in a planar flow during die filling.

The Effect of Electromagnetic Vibration on the Continuous Elimination of Inclusions in Molten Aluminum Alloy by Electromagnetic Force

The separation system including a DC electric field with steady magnetic field was adopted for removal of inclusion in molten Al alloy. But, very small inclusions, which less than 10 ㎛ are not eliminated. So, firstly, small inclusions are agglomerated by low frequency electromagnetic vibration. And then, we adopting the previously used electromagnetically inclusion removal process. Experiments were carried out on commercial die casting aluminum alloy A380 (JIS: ADC 10). Inclusion was separated continuously. XRF was used for compositional test and PoDFA for cleanliness test. Chemical composition of specimen was not changed and UTS, elongation and cleanliness were increased.

Rheology and Foaming Characteristics of Melt for Metal Foam

Metal foam was produced by the Melt Foaming Method. In this foaming process, the surface tension and the viscosity of molten Al (recycled waste Al) and Mg alloy (Az91) that were measured respectively by the ring method and the rotational method are the most important two factors. They surface tension and the viscosity were investigated in the temperature range of about 600-900°C and the effects of the additional surface-active elements were investigated at the about 640°C. The measured surface tension of the molten recycled Al and Az91 decreased linearly with the increasing temperature of Ar gas (99.999%) and SF6+CO2 (1:100) atmosphere. The effect of surface-active elements is a decrease of the surface tension and an increase of the viscosity. The optimal conditions for the foam metal manufacturing are needed the low surface tension and the high viscosity. It is possible that the optimal conditions of the surface tension and the viscosity can be obtained through controlling the amount of adding surface-active elements.

Spherical foam growth in Al alloy melt

Due to the demand of high-tech Al alloy foam with spherical pores, high strength and high energy-absorption capacity has become one of the research foci. The aim of this study is to ascertain the growth regularity of spherical foam in Al alloy melt. Three-dimensional packing model such as face-centered cubic is established to study the spherical foam growth. Theoretical results are compared with experimental ones, and the face-centered cubic model corresponds well with the experiment. It is reasonable to assume that the pores have the same radius, the total pore number keeps unchanged and spherical foam grows with face-centered cubic packing mode. This study presents a useful help to control the average pore radius and film thickness.

<I>In Situ</I> Observations of Solidification and Melting of Aluminum Alloy Using Ultrasonic Waveguide Sensor

The in situ observations of solidincation and melting of an aluminum-silicon alloy (Al -12.6%Si) using an ultrasonic waveguide sensor are presented. The ultrasonic sensor consists of a conventional piezoelectric ultrasonic transducer, a cooling system and a titanium (Ti) rod as an ultrasonic waveguide. The sustainability of the Ti rod in the molten Al alloy is investigated by immersiontests for 1, 4, 8 and 16h at 800' C. The formation of a layer consisting of globular TiAl 3 , disperse AlSi 2 Ti and α-Al phases has been observed at the interface between the Ti and the Al alloy. Ultrasonic pulse-echo measurements of the Al alloy during solidification and melting have been performed using the ultrasonic sensor in temperature range from 200 to 800°C. The longitudinal wave velocity of the Al alloy shows a rapid and significant change from about 3900 to 5600 m/s around the eutectic point, An attempt to measure a solid/liquid interface of the Al alloy has been made at frequency of 2.25 MHz. The reflected echo from the interface undergoing directional solidification has been observed. The position and growth rate of the interface have also been determined from the reflected echo.

Al合金溶湯における鋼の溶損におよぼす炭化物の量と種類の影響

Al合金溶湯における鋼の溶損におよぼす炭化物の量と種類の影響

Fabrication of Composite Materials Using Al Scrap and Wasted Glass

Model experiments were performed for fabricating composite materials using Al scrap and waste glasses. Significance of the fabrication using the waste matters was discussed from an environmental point of view. Al alloy having composition of the Al scrap was melted and infiltrated into a soda-lime glass beads' bed by a vacuum process. Reaction layer was formed at the interface between the glass beads and the molten Al alloy. The layer thickness of 50 microns was obtained after 1 h reaction. The composite materials showed a strong bonding between the filler (the glass particles) and the matrix. Variation of the layer thickness was measured at various conditions of the reaction time and temperature. Distribution of the metal elements in the microstructure of the composite material was analyzed with SEM/EDX. It was shown that not only Si but also some elements were removed from the glass to the Al alloy matrix. Behaviors of the other elements were discussed, considering the thermodynamics. Compression test of the composite materials was performed. They fractured in a brittle manner once, however, after the fracture, they were not broken into pieces, but followed by the ductile deformation.

The two steps thermal decomposition of titanium hydride and two steps foaming of Al alloy

Two steps foaming (TSF) technique was proposed to prepare shaped Al alloy foam. Based on the thermal decomposition kinetics equation of titanium hydride, the relationship between two steps thermal decomposition kinetics of titanium hydride and two steps foaming Al alloy melt was studied. Two steps thermal decomposition curve of titanium hydride under increasing and constant temperature was calculated respectively. The hydrogen mass needed in the second foaming step was also calculated. Results showed that the hydrogen mass of the second thermal decomposition of titanium hydride is enough for the second foaming step in the condition of as-received Al melt foaming. Experimental and theoretical results indicate that two steps foaming technique can be used to prepare Al alloy foam with high porosity, shaped components and sandwich with Al alloy foam core.

Feasibility study of friction stir welding of 6061-T6 aluminium alloy with AISI 1018 steel

The present work demonstrates that friction stir welding (FSW) is a feasible route for joining 6061 aluminium (Al) alloy to AISI 1018 steel. The weld has a good weld quality and is free of cracks and porosity. The tensile failure happened at the boundary between the nugget and thermomechanically affected zone of the base Al alloy, indicating that the weld has a higher joining strength. Despite the fact that the hardness fluctuates strongly within the nugget, the average hardness of the nugget is substantially higher than that of the base Al alloy. During FSW, localized melting of the Al alloy in the nugget occurred, and the molten Al alloy reacted strongly with steel pieces spread through the nugget, which resulted in the formation of the Al-Fe intermetallic compounds, Al13Fe4 and Al5Fe2. The nugget consists of secondary phases including coarse steel pieces and Al-Fe intermetallic compounds, and an Al alloy matrix. These secondary phases contribute to the hardness of the weld.

Interfacial Reactions, Thermodynamics and Kinetics in Doped Aluminosilicate Ceramics/Liquid Al-Alloy Contacting Systems

Doping of alumino-silicate crucibles with MgO, CaO, or BaO aimed for improving their performance towards Al-alloy melts in aluminium foundry industry. Depending on the particular oxide, doping considerably affects microstructure and crystalline state of resulting ceramics, as well as interfacial reactions with Al-alloys at elevated temperatures. Analysis of reaction features, in terms of reaction zone structure, mechanism and kinetics, for each particular doping oxide, indicates that reaction intensity and kinetics follow the order MgO>BaO>CaO.

Fabrication of BN/Al(-Mg) Metal Matrix Composite (MMC) by Pressureless Infiltration Technique

BN/Al(-Mg) metal matrix composite (MMC) was fabricated by the pressureless infiltration technique. The phase characterizations of the composites were analyzed using the SEM, TEM, EDS and EPMA on reaction products after the electrochemical dissolution of the matrix. It is confirmed that aluminum nitride (AlN) was formed by the reaction of Mg 3N 2 and Al alloy melt. Plate type AlN and polyhedral type Mg(-Al) boride were formed by the reaction between Mg 2N 2, BN and molten Al in the composite. The reaction mechanism in the fabrication of BN/Al(-Mg)MMC was derived from the phase analysis results and the thermodynamic investigation.

Hydrogen gas pick-up mechanism of Al-alloy melt during Lost Foam Casting

The hydrogen gas pick-up problem that can occur during Lost Foam Casting was investigated with reduced pressure tests and real castings. The initial hydrogen concentration of the melt and the contact time between melt and polystyrene had a main effect on the hydrogen gas pick-up of Al melt. The hydrogen gas pick-up of Al alloy depended also on pouring temperature and a proper metal front temperature gave the minimum hydrogen pick-up. At a low pouring temperature, the hydrogen went into the melt mainly from entrapped liquid product of polystyrene but at high pouring temperature it was by the gas as well as the liquid product. The mold flask evacuation down to 710 torr decreased the gas porosity down by around 0.4 vol%. The permeability of coating thickness had a great effect because it affects the filling time and the easy removal of liquid polystyrene.

New type of spherical pore Al alloy foam with low porosity and high strength

A computer system for displacement sensor is developed to obtain the real-time curve of the liquid porosity of molten Al alloy foam. The relationship between the curve of Pl-t and the change of the shape of the cells (spherical, similar spherical and polygonal) in the foaming process is analyzed. The changes of cell diameter and cell wall thickness are studied. And the the controlling methods of a new Al alloy foam with spherical pores, low porosity and high strength are developed on this basis. Also, the stress-strain curve during compressive deforma- tion and energy absorption characteristics are investigated and compared with polygonal pore Al alloy foam with high porosity.

Thermal decomposition kinetics of titanium hydride and Al alloy melt foaming process

A temperature programmed decomposition (TPD) apparatus with metal tube structure, in which Ar is used as the carrier gas, is established and the TPD spectrum of titanium hydride is acquired. Using consulting table method (CTM), spectrum superposition method (SSM) and differential spectrum technique, TPD spectrum of titanium hydride is separated and a set of thermal decomposition kinetics equations are acquired. According to these equations, the relationship between decomposition quantity and time for titanium hydride at the temperature of 940 K is obtained and the result well coincides with the Al alloy melt foaming process.