Al Melt Research Articles

On the effect of thermal diffusion treatment on the hot-dipped Al-Si alloy coating on Fe-Cr-B cast steel

The periodic layered structures (PLSs) consisting of alternatively arranged Cr-Al-B MAB phase and FeAl3 were formed in-situ at the (Cr, Fe)2B/pure Al melt interface during hot dip aluminizing (HDA) of Fe-Cr-B cast steel. In the present investigation, HDA of a novel Fe-Cr-B cast steel was carried out in an Al-5.7 wt% Si alloy melt at 750 ℃ for 30 min. The HDA samples were given thermal diffusion treatment (TDT) at 750 ℃. The microstructural evolution of the Al-Si coating during HDA and TDT were analyzed in details. Results showed that Si in Al melt had a great influence on the compositions of PLSs. During HDA, Si atoms in the melt partially replaced Al atoms in the Cr-Al-B MAB phase, and Si-rich phase were rich at the boundary of Cr-Al-B MAB phase. While, during TDT, the Si-rich phase dissolved into the adjacent FeAl3. The formation process of PLSs during TDT experienced the both transformation from the laminar structure formed in the initial stage to the graininess structure at last and from disordered to ordered arrangement.

Boosting the grain refinement of commercial Al alloys by compound addition of Sc

For decades, Al–Ti–B has been widely used for refining commercial Al alloys. However, the addition of Al–Ti–B master alloys to recycled Al alloys suffers from Si-poisoning and cannot achieve desired refinement and thus final strength-ductility. In this study, a novel grain refiner made of Al–Ti–B-Sc has been developed and its application in refining recycled Al–Si–Cu alloys has been quantified using X-ray computed tomography (XCT). It has been found that the new Al–5Ti–1B-0.8Sc master alloy exceed the performance of Al–5Ti–1B in three aspects: (1) formation of Al3(Sc,Ti) heterogeneous nucleation particles other than Al3Ti; (2) dispersing TiB2 by forming TiB2/Al3(Sc,Ti) clusters and increasing Al melt viscosity; (3) reducing the specific surface area of Al3Ti to improve its high-temperature stability. Surprisingly, the compound addition of Sc has been found to further reduce the grain and Si particle size due to accelerated kinetics of α-Al nucleation and diminished Si poisoning. Therefore, this study proposes not only a new master alloy but also a new grain refinement method, which can effectively increase the tensile strength and elongation of recycled Al alloys up to 433.2 ± 10.5 MPa and 3.0 ± 0.1 %, respectively.

Interfacial microstructure evolution and mechanical properties of carbon fiber reinforced Al-matrix composites fabricated by a pressureless infiltration process

In this study, unidirectional carbon fiber reinforced aluminum-matrix (CF/Al) composites were successfully fabricated by using a pressureless infiltration process to infiltrate Ni-coated CFs with Al. The evolution of the interfacial microstructure was investigated. The results showed that the Al–Ni reaction provided the main driving force for infiltration of Al melt into CF bundles by the significantly improving wettability. As the infiltration time increased from 0 min to 8 min, the infiltration behavior gradually improved with fewer defects and better fiber dispersion. Furthermore, the Al–Ni intermetallic compounds (IMCs) transformed from the large-sized primary Al3Ni phase to fine Al3Ni phase with eutectic structure, and were uniformly distributed around the CFs, which was beneficial for transferring the load and preventing the crack propagation. However, the harmful Al4C3 phase grew up at the interface. The ultimate tensile strength (UTS) of the CF/Al composites with the optimal infiltration time of 6 min was 135 ± 4 MPa, which was 121.3 % higher than that of the Al matrix.

Removal of Low-Content Impurities from Pure Al by Supergravity Combined with Semi-Solid Method

Recently, the purification technology for high-purity aluminum (Al) has become the focus and difficulty of the majority of researchers. In this study, a novel approach for removing iron (Fe) impurities from pure Al via combining the supergravity field and semi-solid refining was proposed. Various separation temperatures (T), holding times (th), and separation times (ts) were applied within a gravitational field to explore their impact on the purification process and its underlying mechanisms. The optimal conditions were achieved at T = 653 °C, th = 40 min, ts = 3 min, and a gravity coefficient G = 1000, with the loss rate of purified Al reaching up to 4.1% and the removal rate of Fe reaching 81.9%. The Fe content in pure Al was reduced from 0.32 wt.% to 0.06 wt.%. Moreover, the purified mechanism of supergravity in a semi-solid method was reported for the first time. It was concluded that supergravity could decrease the value of the effective distribution coefficient (ke), thereby promoting the continuous migration of Fe impurities at the solidification interface into the liquid phase. The Fe-rich phase in the Al melt was completely filtered to the lower part of the crucible in the supergravity field, completing the further purification of the pure Al.

Microwave plasma-produced Al/Al2O3 microparticles as precursors for high-temperature high-strength composites

Microwave plasma-produced Al/Al2O3 microparticles as precursors for high-temperature high-strength composites

Synthesis and characterization of Al-AlN composite

In the present work, Al-AlN metal matrix composite is synthesized by liquid metallurgy route. AlN particles are difficult to wet by molten Al because of their sinking tendency due to higher specific gravity. To retain them in a matrix for more time, it is attempted to add sintered powder compacts of Al and AlN into the Al melt at 1173 K using the vortex method. For the conceptual interfacial study of matrix and reinforcement, separate batches of Al-AlN composites with and without Mg are synthesized. The angle formed by particulate with matrix was studied to understand the bonding between them. Interfacial angle measurement indicates the improvement in the bonding of AlN particulates in Al matrix. Hardness is improved by 52% and specific wear rate reduced by 37% for Mg-modified Al-AlN composite than unmodified Al-AlN.

Liquid Metal Corrosion of Mo and TZM in Al Melt: Mechanism and Kinetics

Liquid Metal Corrosion of Mo and TZM in Al Melt: Mechanism and Kinetics

Mechanistic understanding of strengthening in a novel MXene/AlSi10Mg matrix composite processed by laser powder bed fusion

The fabrication of high-performance two-dimensional nanosheets strengthened Al matrix composites (AMCs) is challenging due to the agglomeration issue of traditional nanosheets (graphene) and their high reactivity with Al powder. To address these concerns, Ti3C2 MXene nanosheets with superior chemical stability were employed as a substitute for graphene in this study. Furthermore, a novel MXene/AlSi10Mg composite powder for the laser powder bed fusion (LPBF) was synthesized using a powder coating strategy. The approach involves three steps, including intercalation treatment of MXene flakes, uniform dispersion of the delaminated MXene nanosheets in aqueous solution, followed by the powder coating treatment using a solid-liquid fluidized bed. Differing from conventional methods for making powder mixtures, such as mechanical blending and ball milling, our powder coating approach achieved uniform distribution and high purity of MXene on the surface of AlSi10Mg powder, while maintaining the original sphericity and flowability of powder. The MXene-coating exhibited exceptional stability under intense conditions of high-energy laser exposure and high-temperature Al melt, enabling the successful retention of MXene nanosheets after LPBF processing. Experimental results show that the retained MXene effectively strengthened the Al matrix through load transfer from Al matrix, pinning effect on the movement of grain boundaries, and inhibiting effect on the deformation and fracture of eutectic Si. Consequently, compared to the bare AlSi10Mg sample processed by LPBF, a small addition of MXene (0.25 wt%) yielded a significant improvement in tensile strength (over 60%), while maintaining an acceptable ductility.

Preparation of ultrafine (W,Mo)B, (W,Mo)B2.5 and (Mo,W)AlB solid solution composite powders

In this study, ultrafine borides powders including (W,Mo)B, (W,Mo)B2.5 and (Mo,W)AlB were successfully fabricated via boronizing ultrafine W-Mo solid solution composite powder with B4C as the boron source under the assistance of Ca melt or Al melt. Ultrafine W-Mo solid solution powder was obtained by using a two-stage reduction route to reduce the precursor powder synthesized by spray drying. Meanwhile, the effects of Mo/W ratio on the phase composition, morphological characteristics and particle size distribution of boride solid solution composite powder were thoroughly investigated. The shift of diffraction peak in the XRD spectrum, the linear change of lattice constant and the homogeneous distributions of W, Mo, B and Al in the EDS energy spectrum comprehensively confirmed that the boride solid solution with different Mo/W ratios could be prepared. Due to the essentially insolubilities of W and Mo in Ca melt, the (W, Mo)B grains grew following a template growth mechanism, and inherited the nearly spherical morphology feature of ultrafine W-Mo solid solution composite powder with a particle size of approximately 200 nm. Nonetheless, as a result of the high solubilities of W, Mo, and B in Al melt, the process of dissolution-precipitation led to the formations of flaky (W, Mo)B2.5 and short rod-shaped (Mo, W)AlB.

Effect of Mn Addition on Microstructure, Mechanical Properties and Die Soldering of Rheocasting Al-7Si-0.3Mg Alloys

The effect of Mn additions (up to 0.8 wt.%) into Al-7Si-0.3Mg alloy on the microstructure, mechanical properties and die soldering was firstly investigated in gravity die casting conditions, with the aim to obtain an optimized Mn addition level. Especially, the stirring testing on H13 die material was used to elucidate the effect of Mn additions on the Fe concentration in the Al melting as a function of melting temperature (690 °C) and holding time (up to 32 h), which can provide an indirect sign of die soldering. On this basis, the addition of 0.6wt.%Mn into Al-7Si-0.3Mg alloy was found to be beneficial for microstructure, strength and die soldering. Secondly, rheocasting of Al-7Si-0.3Mg alloy without (Mn-free alloy) and with 0.6 wt.% Mn (Mn-containing alloy) was performed. The addition of 0.6wt.%Mn into Al-7Si-0.3Mg alloy was found to have following effects: (i) solidification temperature of α-Al is increased and a higher (about 20 °C) rheocasting temperature is therefore needed, but no significant die soldering problem was observed even with increasing casting temperature, (ii) Mn-containing phase forms along grain boundaries and within Al matrix, which increases tensile and yield strength but decreases elongation in as-cast, T5 and T6 conditions, (iii) number density and volume fraction of pores increases, and (iv) die soldering slightly improves. This paper demonstrates that the addition of 0.6wt.%Mn into Al-7Si-0.3Mg alloy is beneficial for microstructure, strength and die soldering in both gravity die casting and rheocasting conditions.

Effects of Zn and Si on the microstructure evolution of the Cr-Al-B MAB phase contained in the periodic layered structure formed in-situ

The MAB phases gain large attention in today's world because of their combination of metallic and ceramic. In our previous work, the periodic layered structures (PLSs) containing Cr-Al-B MAB phase were formed at the Fe-Cr-B cast steel/molten Al interface. This work reports the preparation method of the new A-site alloyed Cr-Al-B MAB phase through hot-dip aluminizing (HDA) in different Al melts and subsequent thermal diffusion treatment (TDT) of Fe-Cr-B cast steel. It was found that the Zn and Si in the Al melts had great effects on the formation and microstructure evolution of the Cr-Al-B MAB phase formed during HDA and TDT. Both Zn and Si could partially replace the Al atoms in Cr-Al-B MAB phase, leading to forming a solid solution with double A atoms. The Cr-(Al, Zn)-B and Cr-(Al, Si)-B MAB phases were achieved by A-site replacement in Cr-Al-B MAB phase. Meanwhile, Zn thickened the thickness of this MAB phase, while, Si decreased that of the MAB phase. However, when they were dopped simultaneously, Zn atom preferentially replaced Al atom in Cr-Al-B MAB phase with that of the substitution of Si not happening.

Fabrication and reaction mechanism study of Co(OH)F@Al nanowire arrays: A functional fluorine-containing metastable intermolecular composite

Metastable intermolecular composites (MICs) comprising solid fuels and oxidizers at nano-scale exhibit high energy densities and fast reaction speeds. As most metal and metalloid fuels are passivated by the natural oxide layer on the surface which acts as a reaction barrier, fluorine-containing oxidizers are of particular interest to promote the reactivity through interfacial fluoridation. In this work, cobalt hydroxy fluoride (Co(OH)F) was introduced as a functional fluorine-containing oxidizer, and core-shell structured Co(OH)F@Al nanoarray was fabricated onto a glass substrate. The thermal behavior and reaction mechanism of pure Co(OH)F and Co(OH)F@Al composites were thoroughly investigated, and Co(OH)F@Al was compared with CoO@Al and Co3O4@Al with identical morphology. In the Co(OH)F@Al composite, a pre-ignition reaction was observed which was attributed to the etching of Al2O3 shell by HF and the fluoridation of Al core by HF and CoF2. With the assistance of pre-ignition reaction, Co(OH)F@Al can complete main exothermal reaction before Al melting in a solid-state mechanism, and its peak temperature is around 200 ℃ lower than those of MICs employing CoO and Co3O4 as oxidizers.

On the mechanism of Si-promoted destabilization of TiCx particles in Al alloys

TiCx is an excellent composite strengthening particle and grain refiner for Al alloys. However, the stability of TiCx is poor when solute Si exists in Al alloy melts, which significantly depresses its strengthening and grain refining effects. In this work, the destabilization mechanisms of the TiCx particles in Al-Si alloy melt with a composition of Al-7Si-7.5TiC were explored via experiments, first-principles calculations and thermodynamic calculations. The experimental results show that Si atoms diffuse into TiCx and Ti atoms are released into the Al melt to form a Ti-rich transition zone during the insulation of TiCx in Al-Si melt, and the TiAlySiz and Al4C3 phases are solidified in the Ti-rich zone and at Ti-rich zone/TiCx interface, respectively. The first principles calculations show that the low formation energy of C vacancies facilitates the rapid diffusion of Si atoms in TiCx, while the doping of Si atoms reduces the energy barrier of diffusion of Ti atoms in TiCx and promotes the formation of Ti-rich zones. The thermodynamic calculations show that the wide crystallization temperature range of the destabilized product TiAlySiz phase is the key to continuous decomposition of TiCx particles. In addition, the driving force of the main destabilization reaction of TiCx in the Al-Si alloys is about 44 times higher than that in the Al alloys without Si addition. This indicates that the presence of solute Si remarkably promotes the subsequent decomposition process of TiCx in the Al-Si alloy melts.

Composition and Miocene deformation of the lithospheric mantle adjacent to the Marlborough Fault System in North Canterbury

ABSTRACT Mantle xenoliths in a nephelinite in the Little Lottery River provide insight into the Miocene mantle adjacent to the Australia-Pacific plate boundary in N Canterbury. The xenoliths comprise peridotite and pyroxenite extracted from depths of ∼ 40 to 60 km. The olivine Mg# < 89, a lack of spinel and occurrence of ilmenite, elevated bulk Cr and Al, light rare Earth element (REE)-enriched clinopyroxene, and 87Sr/86Sr15 Ma clinopyroxene populations (0.7029–0.7047) in most harzburgite and dunite samples, and in all lherzolite, wehrlite, olivine websterite and orthopyroxenites, indicate that most are the product of reaction of depleted peridotite with Fe, Ti, Al and light REE-bearing silicate melts of basaltic or similar composition. Available isotopic data indicate that the xenoliths could be derived from mantle lithosphere beneath the Hikurangi Plateau, in which case the reactive melts may have been associated with the Cretaceous plateau formation. Extensive recrystallisation of olivine indicates that portions of this lithosphere mantle were affected by the deformation close to the time of entrainment. Since the eruption occurred at ∼ 15 Ma, these textures require that the mantle lithosphere in this area was deforming before formation of today's expression of the proximal Hope Fault strand of the Australia-New Zealand plate boundary.

Three bond modes of basic refractories used for Ruhrstahl Heraeus degassing process

AbstractMagnesia–spinel brick and unburnt periclase–spinel–Al brick are being employed as a substitution of traditional magnesia–chrome brick in the chromium‐free campaign of lining materials in Ruhrstahl Heraeus (RH) degasser. These three materials are investigated, in terms of physical properties, corrosion resistance and flexibility by wedge splitting test. Tracking their physical alterations and chemical reactions through burning or heating, three bond modes are discovered. Magnesia–chrome brick is subject to a series of phase transformation with rising temperature to yield a liquid envelop around chromite‐ore particles, to further form porous rim while liquid is gradually absorbed by surrounding magnesia and eventually to precipitate secondary chromite spinel lied between magnesia particles by thoroughly dissociating chrome ore. The precipitated chromite spinel functions as the featured bond that enhances hot strength and corrosion resistance to slag, and additionally liquid coexistence improves the flexibility. The direct bond mode of magnesia particles in magnesia–spinel brick endures slag penetration by immanent character of MgO. Spinel incorporation in magnesia effectively improves thermal shock resistance. Due to minor negative value of permanent linear change after reheating, further sintering (densifying) in using at high temperature would bring a risk of loosening and open joints of magnesia–spinel lining. While used in RH degasser, unburnt periclase–spinel–Al bricks undergo a miraculous process of metallic Al melting, gaseous AlN and AlON formation, MgAlON whiskers germination combined with gaseous Mg reduced, and micron‐size whisker network bond domination in their matrix. Such a whisker‐network bond renders the material a successful eco‐friendly alternative to magnesia–chrome refractory.

Ab initio study of chemical effect on structural properties of Ti–Al melts

We study chemical effect on the structural properties of Ti–Al melts, with the Al concentration systematically changed, via ab initio molecular dynamics simulations. By calculating the partial coordination numbers, we find a preferred connection between the nearest neighbors for Al–Ti pairs. This induces an excess Ti coordination in the cluster characterized by local five-fold symmetry in Voronoi tessellation. Structural entropy measured from the diversity of Voronoi polyhedrons shows an intriguing non-monotonic tendency with concentration: it first decreases to a minimum value at Ti40Al60, and then increases beyond this concentration. This implies a more ordered local structure induced by the chemical interaction at the intermediate compositions. The spatial correlation among the crystalline-like or the icosahedral-like clusters also exhibits the highest intensity for Al–Ti pairs, verifying the important role played by the chemical interaction in the local structure connectivity.

Demonstrating an altered metal oxidation reaction mechanism correlated with variations in surface energy

Thermal processing of powder media such as annealing and quenching alters particle surface properties and can influence the powder's reactivity. In this study, thermogravimetric analysis (TGA) was performed with micro-sized (4 µm characteristic particle diameter) aluminum (Al) powder. Two powders were examined, namely, untreated Al (UN Al), i.e., procured from the manufacturer, compared with thermally processed Al by annealing and quenching (i.e., called super-quenched aluminum, SQ Al). TGA experiments were designed to compare the rate of oxidation of both materials. A new data processing technique was introduced that allows for a direct demonstration of altered reactivity by comparing the sample behavior during heating and cooling. The approach analyzes a normalized derivate drop of mass gain data throughout a programmed heating and cooling cycle depending on particle exposure time to oxygen at select temperatures. Results clearly confirm a difference between SQ Al and UN Al at temperatures around 600 °C, i.e., just below the Al melting temperature. The powders were also characterized using inverse gas chromatography (iGC) that showed a substantially higher surface energy of UN Al. Based on the experimental results, there is a correlation between Al reactivity and particle surface energy that substantiates recent observations of two different modes of Al particle combustion. Particle surface energy can be controlled to affect the mechanism for metal oxidation thereby affecting the rate of metal combustion.

Effect of mold and core preheating temperature on corrosion resistance of casting Al-12Si alloy U-shaped cooling channel

Temperature has an important impact on the corrosion resistance of mold with cooling channels prepared by casting method. The effect of preheating temperature of the mold and the carbon fiber core on the roughness and corrosion resistance of U-shaped cooling channels made of Al-12Si alloy was examined in depth. The experimental results suggest that as the preheating temperature increased from 273 K to 573 K, the roughness of the inner wall of the cooling channel reduced from 96.6 µ m to 77.0 µm. When the preheating temperature continued to increase to 723 K, the roughness increased to 85.3 µm. The wetting between the Al melt and the carbon fiber will reduce micro bubbles and waves on the channel wall as the preheating temperature rises, thereby reducing the roughness. However, with the further increase of preheating temperature, it will increase the solidification time of the Al melt. At this time, the carbon fiber and Al melt will take more time to react, which increases the roughness of the channel wall to a certain extent. The results of exfoliation corrosion show that the larger roughness will aggravate exfoliation corrosion. The prolongation of high temperature reaction time between the carbon fiber and the Al melt will lead to the segregation of Si, which is easy to cause intergranular corrosion. Therefore, reasonable preheating temperature has an important impact on the roughness and corrosion resistance of U-shaped cooling channels.

An anti Si/Zr-poisoning strategy of Al grain refinement by the evolving effect of doped complex

The issue of how to avoid the poisoning phenomenon of α-Al grain refinement caused by special elements (such as Si and Zr) has always been the focus of research attention. In this work, the anti Si/Zr-poisoning of α-Al grain refinement was achieved by the evolving effect of a doped TCB complex, which is constituted by B-doped TiC (B-TiC) and C-doped TiB2 (C-TiB2). The results indicate that B-TiC in the TCB complex can release Ti atoms in Al melts, and the unique C-TiB2 particles have a reproduction subsequently. The released Ti atoms by B-TiC during the evolution process act as the solute, limiting the grain growth and assisting in the refinement of the α-Al grains. Furthermore, the density functional theory calculations show that the C atoms in the interior of C-TiB2 tend to enhance the adhesion energy of the C-TiB2/Al interface, improving the nucleation potency for α-Al on C-TiB2 in the Al-Si alloys or Zr-containing Al alloys. The average grain sizes of Al-7Si-0.4Mg and Al-5Cu-0.15Zr with inoculated TCB complex can be refined to 84 ± 7 μm and 63 ± 4 μm from 784 ± 58 μm and 402 ± 32 μm, respectively. Thus, the anti Si/Zr-poisoning of Al grain refinement is synergistically realized based on the dynamically evolving TCB complex. These findings provide a new direction for the grain refinement of the Al-Si alloys or Zr-containing Al alloys, as well as guidance on further research and development of grain refiners.

Production and characterization of Al–Cu binary alloy produced by using novel continuous casting process

Abstract Aluminium (Al) and its constituent alloys has been consistently favoured as a promising material for industrial applications. In conventional casting technique of Al alloys, alloying elements are amalgamated in molten pool of Al melt followed by manual skimming. In contrast, batch type manufacturing includes intrinsic mixing and casting discontinuity, which negatively impacts the flexibility and cost-effectiveness of the process, resulting in a decline in the overall efficacy of the process. In the present study, a novel continuous casting processing route has been used to make Al–Cu binary alloys of different compositions. The newly designed technique makes use of a novel mechanical force convection technology, as well as bottom feeding of the molten metal and alloying element throughout the manufacturing process. The bottom feeding along with rotational swirl ensures better amalgamation of alloying element. Feed rates of Al melt and Al–Cu master alloy were mathematically modelled to obtain the desired alloy composition. The microstructural characterization of the developed alloys exhibit Al–Cu intermetallic phase invariably distributed throughout the sample, which concludes a better performing processing route to prepare Al–Cu binary alloys.