Molten Al Alloy Research Articles

Solid-State Transformation of Iron-Rich Intermetallic Phases in Al-Cu 206 Cast Alloys During Solution Heat Treatment

The solid-state transformation of the iron-rich intermetallic phases in Al-Cu 206 cast alloys during the solution heat treatment was studied by using Scanning Electron Microscope (SEM), Electron Back Scattered Diffraction (EBSD), Differential Scanning Calorimeter (DSC), and Transmission Electron Microscope (TEM). At a normal solution treatment temperature of 793 K (520 °C), no visible variation is observed for the β-Fe phase solidified from the Al alloy melt. With increasing soaking time, however, the Chinese script α-Fe becomes unstable and progressively transforms into platelet β-Fe, termed as solid-state-transformed (STed) β-Fe to distinguish it from the β-Fe directly solidified from the Al alloy melt. The STed β-Fe preferentially nucleates on the α-Fe and then grows from the α-Fe/Al interface into α-Fe and/or Al matrix with a much higher growth rate in the α-Fe. The incomplete solid-state transformation from α-Fe into STed β-Fe leads to the fragmentation of the α-Fe. The formation of the STed β-Fe with increasing size and volume fraction after longer soaking time can deteriorate the tensile properties.

Silicon dissolution and interfacial characteristics in Si/Al composites fabricated by gas pressure infiltration

The silicon dissolution and interfacial characteristics of Si/Al composites were investigated by microstructure analysis and thermodynamic calculation. A new method of gas pressure infiltration was proposed to fabricate the Si/Al composites with near-net shape. The interfacial characteristics were examined using SEM, TEM, EDS and X-ray Diffraction, especially, silicon particles with reaction products were extracted through the electrochemical etching. The results show that some Si particles have been dissolved and a lot of crusts filled with Al matrix are left. The SiO2 layer in Si/Al composites has three functions: to enhance the interfacial strength by interfacial reactions between Si particles and Al matrix, to serve as barriers to prevent the Si particles from being dissolved by molten Al alloy, and to join Si particles to form Si preform. However, the barriers will not perform these functions when they are damaged. The SiO2 barriers are consumed by molten Al alloy, and the major phase in the interfacial reaction products between the SiO2 barriers and the molten Al is Al2O3, while MgAl2O4 is the minor phase. Furthermore, the reaction of an equation “4Al (L) + 3SiO2 (S) = 2Al2O3 (S) + 3Si (S)”is the dominant interfacial reaction in the Si/Al composites, which is different from the dominant reaction in SiC/Al composites.

Fabrication of Al/A206–Al2O3 nano/micro composite by combining ball milling and stir casting technology

Al206/5vol.%Al2O3p cast composites were fabricated by the injection of reinforcing particles into molten Al alloy in two different forms, i.e. as Al2O3 particles and milled particulates of alumina with Al and Mg powders. The resultant milled powders (Master Metal Matrix Composite (MMMC)) were then added into the molten Al alloy both in semi-solid state and above liquidus temperature. Effects of powder addition technique, reinforcement particle size and casting temperature on distribution and incorporation of reinforcing particles into molten Al alloy were investigated. Morphology evolution of powders during milling, microscopic examinations of composite and matrix alloy were studied by scanning electron microscopy (SEM). X-ray diffraction (XRD) analysis was also used to determine the possible interaction between powders after ball milling process. Results showed that injection of powders in the form of MMMC leads to considerable improvement in incorporation and distribution of Al2O3p in the Al206 matrix alloy leading to the improvement in tensile properties. Improvement in tensile properties is attributed to the better wetting of Al2O3p by melt as well as removing microchannels and roughness on alumina particles as a consequence of ball milling process.

Oxidation Resistance and Corrosion Resistance of AlTiCrON Multilayered Coatings on AISI M2 Tool Steel

This study utilized the reaction of O2/N2 gases and Al0.67Ti0.33/Cr (99.9%) dual targets to synthesize (Ti,Al)ON/CrON multilayered coatings on AISI M2 steel by cathodic arc deposition system. Thermal stability and corrosion resistance of the multilayered coatings for aluminum die casting applications, along with coating structure were investigated. The results showed that the structure of multilayered coatings was a B1 NaCl type. The formation of oxide phases by introducing oxygen to react with Al, Cr, and Ti elements was confirmed by XPS. The thermal stability of oxygen-doped AlTiN/CrN coatings was higher than that of one without oxygen. After the immersion tests in Al-alloy melt, the oxygen-doped AlTiN/CrN coatings deposited at the O2/N2 ratio value of 0.3 had the best improvement on the corrosion resistance among all the coated specimens.

FAILURE MODES OF PVD COATINGS IN MOLTEN Al-ALLOY CONTACT

This paper deals with a study of the failure mode of thin PVD coatings in alternated contact withmolten aluminum alloy. CrN and ZrN monolayer coatings deposited through cathodic arcevaporation were used. The coatings morphology was assessed by SEM and their mechanicalproperties evaluated by nanohardness test performed at room temperature. An experimental testrig which cyclically immerses coated steel samples in molten Al-alloy and in a cooling bath wasapplied. The thermal gradient from the coating to the steel core was exalted by internal coolingchannels placed in the internal cavity of samples. Periodical SEM inspections were performed toassess the damaging levels introduced by the test and to study the related decrease of substrateprotection capability. Descriptions and interpretations of the damages evolutions were derived.The main conclusions achieved are that both coatings suffered by the formation of corrosionpits, which were due to a corrosion attack of the steel substrate localized at coating defects sites.In particular, at pores locations the corrosion was fast, whereas at droplets sites it required acertain incubation time. Once corrosion pits were formed they exhibited an initial tendency toexpand laterally, but they did rapidly stabilize in terms of lateral dimensions. Later on twodifferent failure modes acted in ZrN and in CrN. Extended delamination due to a markedmismatch of mechanical properties between the coating and the steel substrate developed inZrN. On the contrary, thermal cracking due to lower hardness levels developed in CrN, but withlimited delamination. Accordingly the steel substrate protection capability was evaluated to behigher in CrN than in ZrN.Keywords: PVD

Microstructure evolution of Mo–Si–Al system during self-propagation high-temperature synthesis

The microstructure and phase constitution of Mo(Si1−x,Alx)2 alloys (x=0.03, 0.1 and 0.4) prepared by self-propagation high-temperature synthesis is first investigated using SEM, EDS and XRD analysis. Then the lattice parameters and adiabatic temperature are calculated. Based on the above experimental and calculated results, the variation mechanism of diffraction peaks and phase transformation subsequence of the Mo–MoO3–Si–Al powders is discussed. Results show that, when the self-propagation reaction is over, there are a homogeneous Mo–Si–Al alloy melt and a fused Al2O3 with lower density at top. Subsequently, MoSi2 or Mo(Si,Al)2 phase nucleates and grows as a primary phase in the Mo–Si–Al alloy melts, and then Al, Si substances are generated from the intergranular residual Al–Si liquid according to Al–Si binary phase diagram. The Al increase in the starting powder mixtures leads to the Al concentration increase in the Mo–Si–Al alloy melt. Consequently, MoSi2 is transformed to Mo(Si,Al)2 to phase in which Si is replaced by Al atoms and Al substance in the intergranular zones increased accordingly.

Effects of V2O5 addition on the corrosion resistance of andalusite-based low-cement castables with molten Al-alloy

Interfacial reactions between Al-alloy and andalusite low-cement castables (LCC) containing 5 wt% V2O5 were analyzed at 850 °C and 1160 °C using the Alcoa cup test. Interfacial reaction products and phases formed during heat treatment of the refractory samples were characterized using scanning electron microscopy (SEM) coupled with energy dispersive spectrometry (EDS) and X-ray diffraction (XRD) analysis. V2O5 addition resulted in the formation of glassy phases, which significantly improved the corrosion resistance. These phases were preferentially corroded by the alloy, due to their glassy nature. However, vanadium formed from reduction, formed intermetallic alloys (V–Al–Si–Mg), which formed an interfacial physical barrier to further alloy penetration.

Effects of AlPO4 addition on the corrosion resistance of andalusite-based low-cement castables with molten Al-alloy

Abstract This paper investigates the effects of AlPO 4 addition on the corrosion resistance of andalusite LCC refractories. Corrosion tests using the Alcoa cup test (850 °C and 1160 °C for 150 h and 72 h, respectively) were conducted to determine the extent of penetration. The addition of AlPO 4 was shown to improve the corrosion resistance of the castables in contact with molten Al-alloy. SEM/EDS analyses of the interfacial reaction zone showed the formation of corundum in the interfacial layer, along with a significant decrease in the phosphorus content in the interface. Thermodynamic calculations revealed that reaction with the alloy leads to the formation of corundum as the reaction product along with gaseous products (phosphorus trioxide gas) and small amounts of aluminum phosphide. Corundum formation at the interface enhances the corrosion resistance of sample due to high stability of corundum against molten Al alloy, while the metal quality is enhanced due to absence of dissolved phosphorus in the metal.

Endurance in Al Alloy Melts and Wear Resistance of Titanium Matrix Composite Shot-Sleeve for Aluminum Alloy Die-casting

Endurance in Al Alloy Melts and Wear Resistance of Titanium Matrix Composite Shot-Sleeve for Aluminum Alloy Die-casting

Effects of Different Boron Compounds on the Corrosion Resistance of Andalusite-Based Low-Cement Castables in Contact with Molten Al Alloy

Effects of Different Boron Compounds on the Corrosion Resistance of Andalusite-Based Low-Cement Castables in Contact with Molten Al Alloy

Effect of grain boundary cracks on the corrosion behaviour of aluminium titanate ceramics in a molten aluminium alloy

The effect of grain boundary cracks on the corrosion behaviour of non-doped aluminium titanate (AT) ceramics was evaluated in a molten Al alloy containing a slight amount of Mg. The corrosion of AT ceramics, in which the AT grains decomposed and subsequently reacted with liquid and/or gaseous Mg to produce MgAl 2O 4, proceeded not only on sample surfaces in contact and non-contact with the melt, but also on open grain boundary crack surfaces in the ceramic interior. Therefore, the corrosion resistance of AT ceramics can be improved by control of their grain size to close open cracks in the molten alloys.

Effects of Different Barium Compounds on the Corrosion Resistance of Andalusite-Based Low-Cement Castables in Contact with Molten Al-Alloy

Effects of Different Barium Compounds on the Corrosion Resistance of Andalusite-Based Low-Cement Castables in Contact with Molten Al-Alloy

Effect of Mg Content on the Characteristics of Al/SiC Nanocomposite Powders Produced via <i>In Situ</i> Powder Metallurgy Method

In the present study the effect of Mg addition on the characteristics of Al/SiC nanocomposite powder particles produced via a relatively new method called in situ powder metallurgy (IPM) is investigated. Commercially pure Al and Al-Mg alloy melts containing different amounts of Mg were used as the matrix alloy. Nano-sized SiC particles with the average size of 60 nm were used as the reinforcing material. The effect of Mg content on the fluidity of the melt as an influencing factor affecting both the process yield and wettability of SiC with molten metal was investigated. The size distribution of produced powders was characterized using a laser particle size analyzer. Scanning electron microscopy was utilized to investigate the possibility of embedding of SiC nanoparticles within the metallic matrix. Results of microhardness measurements together with SEM micrographs and EDS analysis showed that nano-sized SiC particles could be embedded in the relatively coarse Al-Mg powders containing at least 1 wt.% Mg.

Effects of Different Calcium Compounds on the Corrosion Resistance of Andalusite-Based Low-Cement Castables in Contact with Molten Al-Alloy

An experimental study was conducted to investigate the interfacial phenomena between an Al alloy and andalusite low-cement castables (LCCs) containing fixed contents of barium compounds (BaO, BaSO4, and BaCO3) at 1123 K and 1433 K (850 °C and 1160 °C) using the Alcoa cup test. Interfacial reaction products and phases formed during heat treatment of the refractory samples were characterized using scanning electron microscopy (SEM) coupled with energy dispersive spectrometry (EDS) and X-ray diffraction analysis (XRD). The addition of both BaO and BaSO4 led to a significant reduction of alloy penetration into the refractory. Hexa-celsian formation was observed in both these refractories, which drastically increased their corrosion resistance. Barite decomposition was observed at 1373 K (1100 °C) in the presence of alumina and silica, which was the precursor for hexa-celsian formation. Barium silicates were formed in all samples containing additives; however, this did not have any major influence on the corrosion resistance. Solidified eutectics of BaSi2 and α-BaAl2Si2 formed in all these samples, which acted as an interfacial barrier that prevented additional molten aluminum penetration; however, the positive effect of intermetallic formation was offset by glassy phase formation in samples containing BaCO3 as the additive.

切削屑を利用した遠心鋳造法のアルミニウムでの検証

We are proposing a centrifugal mixed-powder method as a novel processing technique to fabricate a nano-particle distributed FGM. If the mixed-powder has been changed into machining chips, an eco-centrifugal casting method can be achieved, since the reduction of necessary power for casting will be expected if recycled materials are used in the melting and casting process. Pure Al or Al-Si alloy melt of 750°C or 800°C is poured into the spinning mold with or without the machining chips. It is found that Al pipe can be fabricated by the centrifugal casting with machining chips. It is also found that the machining chips act as the grain-refiner. Although some pores were found for the cast with the machining chips, the defect can be reduced when the mold is preheated. In this way, Al pipes without casting defect can be fabricated by the proposed method.

Effect of grain refinement on the microstructure and tensile properties of thin 319 Al castings

The structural examinations and tensile properties of thin-section Al castings (319 Al alloy) have been investigated by applying a pattern with different cross sections (2–12 mm). Al–5Ti–1B and Al–5Zr grain refiners were added to the molten Al alloy to produce different levels of Ti (0.01%, 0.05%, 0.1% and 0.15%) and Zr (0.05%, 0.1%, 0.2%, 0.3%, 0.4% and 0.5%) in the castings. From macrostructural studies, it was found that Al–5Zr is less effective in grain refining of 319 alloy in comparison with Al–5Ti–1B master alloy. The optimum levels of grain refiners were selected for determination of tensile properties. T6 heat treatment was applied for selected specimens before tensile testing. Further structural results also showed that thinner sections are less affected by grain refiners. This observation was found to be in a good agreement with tensile test results, where tensile properties of the base and grain refined alloys did not show considerable differences in thinner sections (<6 mm).

Effect of BaSO4 on the interfacial phenomena of high-alumina refractories with Al-alloy

The performance of high-alumina refractories used for aluminium casting significantly impacts the efficiency of metal production. The interfacial reactions with Al-alloys cause corundum and magnesium spinel deposition on the refractory surface, leading to refractory degradation. An experimental study was conducted to investigate the influence of varying barium sulphate (BaSO4) concentrations in a high-alumina refractory on its interfacial reactions with molten Al-alloy in a horizontal tube furnace at 1523 K (1250 °C) under inert conditions. This study showed that the Al-alloy reactions with pure BaSO4 would form barium aluminates at the interface. However, in the Al-alloy/refractory system, the interfacial behaviour was strongly influenced by the relative amount of BaSO4, such that up to 5 wt%, the extent of alloy penetration into the refractory increased with increasing BaSO4 contents. Electron-probe micro-analyser and X-ray diffraction studies indicated that the composition of the interface for these refractories was augmented with barium silicates and diminishing anorthite phases. In the presence of 10 wt% BaSO4, the extent of metal penetration into the refractory decreased, whilst for 20% BaSO4, the penetration was higher; these results were attributed to the interfacial presence of celsian (BaAl2Si2O8) and unreacted barium sulphates, respectively. This study suggests that maximising the celsian formation at the interface is critical for optimising the BaSO4 concentration for improving the refractory’s performance for Al-casting.

Effects of Gating System on the Flow Behaviors during Vacuum Counter Pressure Casting Thin Wall Aluminum Alloy

The flow behaviors of molten Al alloy in sand mould cavity with varied gating system were simulated under vacuum counter-pressure casting and the ingate velocity was predicted using a software package. At same process conditions, the flow behaviors were investigated using electrode contact method. The comparison between the simulated results and the investigated results shows that a good agreement is achieved. The ingate flow velocity exceeding critical velocity and large velocity deviation are detected during filling mould withⅠtypes gating system, resulting in turbulent flow behavior. Whereas, flow behaviors take on stable flow pattern during filling the other mould cavity, although some differences of flow behaviors are present. The small ingate flow velocity and velocity deviation during filling mould cavity with Ⅲ type gating system may be conduce the more stable flow pattern thanⅡtype gating system.

Effect of Foaming Temperature on Pore Morphology of Al/AlN Composite Foam Fabricated by Melt Foaming Method

Al foams whose matrix contains dispersed AlN particles (Al/AlN composite foams) were prepared by a melt foaming method, and the effect of foaming temperature on the pore morphology of the prepared foams was investigated. First, Al/AlN composites were prepared by non-compressive infiltration of Al powder compacts with molten Al alloy in nitrogen atmosphere. Next, the prepared composites were melted by induction heating and foamed at various temperatures using TiH2 powders as blowing agents. The porosity of prepared Al/AlN composite foams slightly decreases with increasing foaming temperature, and the pore morphology of the foam becomes homogeneous simultaneously. When the foaming temperature is 1123 K, homogeneous pores are formed in all over the ingot. This pore homogeneity is probably achieved by the stabilization of the foaming behavior due to the formation of Al3Ti particles in the melt and dispersion of AlN particles.

Fabrication of Al-3.7 Pct Si-0.18 Pct Mg Foam Strengthened by AlN Particle Dispersion and its Compressive Properties

Al-3.7 pct Si-0.18 pct Mg foams strengthened by AlN particle dispersion were prepared by a melt foaming method, and the effect of foaming temperature on the foaming behavior was investigated. Al-3.7 pct Si-0.18 pct Mg alloy containing AlN particles was prepared by noncompressive infiltration of Al powder compacts with molten Al alloy in nitrogen atmosphere, and it was foamed at different foaming temperatures ranging from 1023 to 1173 K. The porosity of prepared foam decreases and the pore structure becomes homogeneous with increasing foaming temperature. When the foaming temperature is higher than 1123 K, homogeneous pores are formed in the prepared ingot without using oxide particles and metallic calcium granules, which are usually used for stabilizing a foaming process. This stabilization of the foaming at high temperatures is possibly caused by Al3Ti intermetallic compounds formed at high temperature and AlN particles. Compression tests for the prepared foams revealed that the absorbed energy per unit mass of prepared Al-3.7 pct Si-0.18 pct Mg foam is higher than those of aluminum foams strengthened by alloying or dispersion of reinforcements. It is remarkable that the oscillation in stress, which usually appears in strengthened aluminum foams, does not appear in the plateau stress region of the present Al-3.7 pct Si-0.18 pct Mg foam. The homogeneity in cell walls and pore morphology due to the stabilization of pore formation and growth by AlN and Al3Ti particles is a possible cause of this smooth plateau stress region.