Al Melt Research Articles

Congruent dissolution of Al2O3 in a K-disilicate melt, with constraints on the reaction mechanism

High resolution O 1s X-ray Photoelectron Spectroscopy (XPS) was employed to determine oxygen speciation in 31 mol% K2O silicate glass containing 0.0, 1.0 and 3.0 mol% dissolved Al2O3. Highly resolved bridging oxygen (BO) and non-bridging oxygen (NBO) peaks were observed. The NBO peak intensity decreased and the BO increased with dissolution of Al2O3. The enhanced BO intensity is localized at two binding energies (BE), one characteristic of a Si-O-Si moiety (e.g., quartz, or v-SiO2), the other of a Si-O-Al moiety (e.g., kyanite, Al2SiO5). The dissolution reaction proceeds in two steps; NBO− of a Q3 species attacks and bonds to an under-coordinated surface Al atom of crystalline Al2O3. The reaction produces a Si-O-Al surface species thus converting the attacking NBO to a BO and altering the reactant Q3 species to a Q4 product species:[Q3]−melt + [AlO1.5]surface → [Q4]0melt + [AlO2]−meltThe second step involves reaction of [AlO2]−melt with K+converting it from a modifier cation to a charge compensator, resulting in the polymerization reaction:[K-Q3]0melt + [AlO2]−melt → [Q4]0 + [KAlO2]0melt + 1/2O2−The stoichiometric reaction is the sum of the two:[Q3]−melt + [K-Q3]0melt + [AlO1.5]surface → 2[Q4]0 + [KAlO2]0melt + 1/2O2−Al species detached from the solid surface initially must be bonded to some NBO. Within the melt, nucleophilic substitution attack of the Al-bearing species by Q3 species converts NBO to BO, resulting in [KAlO2]melt being bonded four BOs. This reaction may not go to completion in all melts, depending on dissolved Al content and melt composition.

Boronation reaction between molybdenum or tungsten powder and boron carbide in aluminium melt

Molybdenum or tungsten borides are excellent high-temperature ceramics or electrocatalysis materials. In this paper, Mo or W borides were prepared by boronizing Mo or W powder in Al melt with B4C as boron source. By thermodynamic calculation, the feasibility of preparing various borides and the stability of borides in Al melt were evaluated. Through high temperature reaction at 1523 K and the following acidic leaching, single phase MoAlB, W2B5, WB, and W2B5 powders were successfully synthesized. Owing to the decarburizing function of Al melt, C contents of various boride products were below 1 wt%. In addition, the phase transition processes of various products in the synthesis stage were revealed.

Improved grain refinement in aluminium alloys by re-precipitated TiB2 particles

Al-Ti-B master alloys are widely used to refine aluminium alloys. The reported researches demonstrate that excellent grain refinement result can be achieved only with the coexistence of solute Ti and TiB2 particles of a proper average radius and a narrow radius distribution. However, the traditional grain refinement method can’t meet the requirements for manufacturing high-quality aluminium alloys due to the large radius and wide radius distribution of TiB2 particles in master alloys. This work proposes a new idea for improved grain refinement in aluminium alloys by re-precipitated TiB2 particles. The TiB2 particles with a narrow radius distribution and a small average radius in Al melt are first prepared. The resultant melt is then directly employed to refine aluminium alloys. An improvement in grain refinement result is achieved compared with the traditional refinement method.

Synthesis of Ti3SnC2–Al2O3 composite by mechanical alloying and subsequent heat treatment

A Ti 3 SnC 2 –Al 2 O 3 composite was produced by mechanical alloying and subsequent differential thermal analysis (DTA) of 3TiO 2 /4Al/1Sn/2C powder mixture. The starting powder was milled up to 40 h. To determine the formation mechanism, a 40 h milled powder was evaluated by DTA. X-ray diffraction was used to evaluate powder samples. Later, morphological and microstructural characteristics of the samples were obtained by high-resolution scanning electron microscopy. Followed by milling, the patterns of X-ray diffraction showed a homogeneous distribution of fine reactant powders without new phases that after 40 h of milling. According to the DTA, several thermal events occurred during the 40 h of milling and Ti 3 SnC 2 /Al 2 O 3 was formed, consequently. The formation mechanism of Ti 3 SnC 2 /Al 2 O 3 composite consisted of Sn melting, Al melting, TiO 2 reduction, Ti 5 Sn 3 and TiC formation, and reaction among Ti, C, Ti 5 Sn 3 and TiC, as well as Ti 3 SnC 2 formation.

Formation mechanism of Ti3AlC2 in TiO2–Al–C/TiC systems at high temperatures

Ti 3 AlC 2 /Al 2 O 3 composites were synthesized by aluminothermic reduction of TiO 2 /Al/C and TiO 2 /Al/TiC. The effects of carbon sources (carbon black and TiC), steps heating-up profile, and Al-excess of raw materials composition on the Ti 3 AlC 2 content in final products were investigated. The results showed that in contrast with carbon black, TiC used as a carbon source is beneficial to the formation of Ti 3 AlC 2 at lower temperatures. However, Ti 3 AlC 2 content in the product with carbon black was improved by the steps heating-up profile and Al-excess, promoting intermediate phases TiAl 3 and TiC. Furthermore, the formation mechanisms of Ti 3 AlC 2 with different carbon sources in aluminothermic reaction systems were also elucidated. For the TiO 2 /Al/C system, Ti 3 AlC 2 is precipitated from the Ti–Al melt at high temperatures via the dissolution-precipitation mechanism, which has slower nucleation but faster growth. In contrast, in the TiO 2 /Al/TiC system, Ti 3 AlC 2 is mainly growing from the intact TiC grains through the epitaxial nucleation mechanism, which has faster nucleation but lower growth.

Impact of preheating on the mechanical performance of different MgO–C bricks - Low temperature range

This work complements an initial study regarding the mechanical behavior of MgO–C bricks at 1000 °C. In this case, two bricks bonded with phenolic resin, one of them containing aluminum, were treated at 600 °C and mechanically tested at RT and 600 °C. The thermal treatments attempt to simulate the in-service steelmaking ladle preheating process. At low temperatures, the binder pyrolysis is one of the main transformations and the Al melting neither its chemical reactions occur on a large scale yet. To evaluate the effects as the pyrolysis progresses, the soaking time at 600 °C was varied from 1 to 3 h. Although without significant chemical activity, the presence of Al affected the mechanical behavior of the tested bricks. The consolidation of the C–C network coming from the binder pyrolysis was identified as the main factor responsible for counterbalancing the material's degradation by microcracking. The heating combined with the low compressive pre-load applied on the tested specimens appears to close the microcracks and pores.

SiC reinforced AlSi10Mg composites fabricated by selective laser melting

In this study, a 10 wt% SiC-reinforced AlSi10Mg-based composites is prepared by selective laser melting (SLM) process. The effect of laser linear energy density on phase morphology, microstructure, and mechanical properties of AlSi10Mg-10SiC composite is investigated. There is relatively higher density, no obvious pores and cracks in the SLM-fabricated AlSi10Mg-10SiC composites with laser linear energy densities ranging from 90.64 J/mm3 to 104.16 J/mm3. The high laser linear energy density promotes the in-situ reaction between SiC particle and Al melt in the melt pool, the Al4SiC4 phase forms during SLM fabrication process. Driven by Marangoni convection, the fine SiC particles and Al4SiC4 phase distributes uniformly. When the laser linear energy density is 104.16 J/mm3, the composite exhibits the highest average microhardness of 208.5 HV0.1. When the laser linear energy density is 90.64 J/mm3, the composite displays the highest yield strength and modulus with values of 408 MPa and 90 Gpa, respectively. During the deformation process of tensile test, the higher modulus SiC particles could withstand greater load transfer, which improves the modulus and yield strength of the composites.

Al/SiC nanocomposites with enhanced thermomechanical properties obtained from microwave plasma-treated nanopowders

Al-based composites with enhanced thermomechanical properties are in high demand. However, obtaining a uniform distribution of the strengthening phase in the metal matrix and achieving a strong metal/ceramic interface is still a great challenge. In this work, nanoAl/nanoSiC powder mixtures after high-energy ball milling were treated with Ar microwave plasma. Plasma processing was designed to remove the initial oxide film covering Al nanoparticles (NPs) and adsorbed impurities from the surface of SiC NPs, improve the wetting of SiC with Al melt, prevent SiC nanoparticle agglomeration, and ensure their uniform distribution in the metal matrix. During plasma treatment, Al/SiC composite particles were obtained, which were subsequently utilized as ready-made structural blocks with uniformly distributed reinforcing SiC NPs to obtain Al/SiC composites with 5, 10, and 30 wt% of SiC. Spark plasma sintered Al/SiC composites using plasma-treated powder mixtures showed approximately 20% higher tensile strength. The addition of 10% SiC led to an increase in hardness by 480% (145 HV), tensile strength by 70% (317 MPa) and 95% (238 MPa) at 25 °C and 500 °C, respectively, compressive strength by 135% (578 MPa), and wear resistance by 35–50%. The effect of point defects at the Al/SiC interface, such as impurity oxygen atoms and Si monovacancies, on the binding energy and temperature-dependent critical shear stress at the interface was assessed using molecular dynamics simulations with machine learning interatomic potentials. Our study demonstrated that the plasma-chemical treatment of Al/SiC powder mixtures is a promising approach for improving the thermomechanical properties of the Al/SiC composites.

Effect of CeO2 on the elevated-temperature wear behaviour of in situ TiB2/A356 composite

Effects of CeO2 on the wear resistance of in situ TiB2/A356 composites synthesised via the reaction of K2TiF6, KBF4 and Al melt were investigated. The results showed that CeO2 was effective in enhancing the wear resistance of TiB2/A356 at all test temperatures. The CeO2 pushed the transition temperature from mild to severe wear by another 50°C. The wear mode of the composite without CeO2 was metal flow and severe wear at 90 N and 200°C, while for the composite with CeO2, the oxidation and delamination wear was the main wear mode at the same load and temperature. The improvement in the wear resistance of the composite was attributed to the increase in thermal stability of the composite due to improved TiB2 dispersion by adding CeO2.

Effects of Zr element on the microstructure and mechanical properties of B4C/Al composites fabricated by melt stirring method

In this study, the addition of Zr element (K2ZrF6) was employed to improve the wettability, inhibit the serious chemical reaction of B4C to Al, and uniformly disperse the B4C particles in the Al melt, during the fabrication of B4C/Al composites via melt stirring method. And the particle distribution, interface microstructure and mechanical properties of the fabricated composites were further investigated. The metallography observation shows that the B4C particles could be effectively introduced to the Al melt with the addition of Zr element, while there were few B4C particles observed in the composites without Zr addition. The XRD analysis indicates that the ZrB2 and ZrC peaks arise with the addition of Zr, where the ZrB2 and ZrC have better chemical stabilization and wettability than the B4C ceramic particles. The SEM, EDS, TEM and SAED analysis shows that the ZrB2 and ZrC interface layer with a thickness of about 200–350 nm on the B4C surface was formed, which could avoid the serious chemical reaction and improve the wettability of B4C to Al, simultaneously. In addition, the easy introduction of B4C particles to the Al melt with K2ZrF6, the formation mechanism of ZrB2 and ZrC layer, and mechanical properties of the composites were also discussed.

Effect of Mg on the microstructure evolution and mechanical properties of 5%TiB2/Al−4.5%Cu composites

Agglomeration behavior of TiB2 particles in 5%TiB2/Al-4.5%Cu composites (all compositions are in wt.% unless otherwise specified) is studied by adding different content of Mg to improve its strength and ductility, a widely used in-situ molten salt reaction process is used to produce the composites. The results show that addition of Mg could not only significantly segregate TiB2 particles but also further refine the α-Al grains and then improve the mechanical properties of the composites on the basis of TiB2 particles. Here, 0.5% Mg is considered the optimum mass fraction for dispersion, refinement, and modification of particles based on the results of investigation. The yield strength (YS), ultimate tensile strength (UTS), elastic Young’s modulus (EM), and Vicker’s hardness (VHN) of the composites in T6 heat treatment are increased to 375 MPa, 486 MPa, 88 GPa, and 167 HV - an improvement of 21.8%, 16.5%, 20.9%, and 9.4%, respectively, versus the original TiB2/Al-4.5%Cu composite (308 MPa, 417 MPa, 63 GPa, and 153 HV). The elongation of the composite is improved by 20.9%. These merits are mainly attributed to addition of Mg, which increases the surface-spread coefficient of TiB2 particles by reducing the surface tension of the Al melt, thereby improving the wettability.

Interaction of Carbon Fiber with a Ti–Al Melt during Self-Propagating High-Temperature Synthesis

Interaction of Carbon Fiber with a Ti–Al Melt during Self-Propagating High-Temperature Synthesis

Wetting of aluminium and carbon interface during preparation of Al-Ti-C grain refiner under ultrasonic field

In the preparation of an Al-Ti-C grain refiner under an ultrasonic field, the mechanism of the wetting behaviour between Al and C was systematically investigated. The results demonstrated that the wetting behaviour was mainly dependent on the wetting of the Al melt on graphite under the ultrasonic field (physical wetting) and the formation and mass transfer of TiC (reactive wetting). The diffusion of Ti atoms and their adsorption around the graphite could contribute to the wetting of Al-C. TiC particles were formed under the high temperature caused by the cavitation effect, and they detached from the interface due to the sound pressure, which resulted in consistently sufficient contact on the wetting interface. Moreover, the wetting and spreading behaviour of the Al melt on graphite under an ultrasonic field were numerically simulated, strongly manifesting that the ultrasonic field could facilitate the wetting of the Al-C interface.

Al Matrix Composites Reinforced by Ti and C Dedicated to Work at Elevated Temperature.

In this paper, the applicability of aluminium matrix composites to high-temperature working conditions (not exceeding the Al melting point) was evaluated. The behaviour of Al-Ti-C composites at elevated temperatures was described based on microstructural and phase composition observations for composites heated at temperatures of 540 and 600 °C over differing time intervals from 2 to 72 h. The materials investigated were aluminium matrix composites (AMC) reinforced with a spatial carbon (C) structure covered by a titanium (Ti) layer. This layer protected the carbon surface against contact with the aluminium during processing, protection which was maintained for the material’s lifetime and ensured the required phase compositions of Al4C3 phase limitation and AlTi3 phase creation. It was also proved that heat treatment influenced not only phase compositions but also the microstructure of the material, and, as a consequence, the properties of the composite.

Fast fabrication of Al3Ti/Al composites using combustion synthesis and melt dilution

A simple method combined combustion synthesis (CS) and melt dilution was utilized to fast fabricate Al3Ti/Al composites. This paper mainly focuses on analyzing the effect of heat source temperature (Ths) on combustion behaviors and reaction products in the 5Al-Ti system. The ultrafast heating rate induced by Ths could activate liquid-solid combustion in powder compacts. Due to the presence of Al3Ti layer acted as a diffusion barrier, it is suggested that reaction kinetics is mainly Ti-diffusion-controlled. Increasing the heating rate remarkably enhances the Ti flux across Al3Ti layer into the Al melt, which in turn releases a higher reaction exothermicity and finally promotes reaction to completion. Based on the above experimental results, a dissolution-precipitation mechanism for Al3Ti formation during CS was established.

Study about improving mechanism of electrical conductivity of AA1070Al treated by a novel composite boron treatment with trace Ti

In this paper, a novel titanium (Ti) assistant composite boron (B) treatment (TBT) was done to improve the electrical conductivity (EC) of AA1070Al and the effects of Ti addition, holding time and stirring on EC of AA1070Al were studied in detail. Results show that the EC of AA1070Al firstly increased and then decreased with the increase of Ti addition, and the optimal addition of Ti is 0.05 wt%, promoting more transition metal (TM) elements dope into composite borides. Furthermore, composite borides can fully sink down at the bottom of Al melts with the extension of holding time, and the optimum holding time of TBT is shorted to 20 min from 90 min (conventional boron treatment). Through TBT and stirring, more TM elements further react with the unreacted B of conventional borides center, thus achieving high boron treatment efficiency and EC. Correspondingly, the content of excessive B is neutralized to 66 ppm from 266 ppm, reduced by 75.2%. At last, the EC of AA1070Al can reach 66.9% International Annealed Copper Standard (IACS), improved by 7.2% compared with without any treatment (62.4% IACS). Based on this, a schematic diagram is drawn to analyze the complex mechanism of a novel composite boron treatment and provide theoretical guidance for Al melt treatment.

Reaction behaviors and specific exposed crystal planes manipulation mechanism of TiC nanoparticles

AbstractTitanium carbide (TiC) nanoparticles with well‐designed exposed crystal planes perform intriguing prospects for functional and engineering applications. In this study, a simple and controllable in situ synthesis strategy was proposed for the synthesis of TiC nanoparticles with specific morphology. Reaction behaviors suggested that most of TiC nanoparticles were formed by an instantaneous reaction between Al3Ti and Al4C3 in the Al‐rich melt and the resultant morphology was controlled by the discrepant growing rates of (100) and (111) crystal planes. In addition, a growth morphology control model was presented for the prediction and manipulation of the morphology of TiC nanoparticles by the doping of different alloying elements Me (Me = Cu, Mg, Mn, Zn, and Si). According to the morphological observations and density functional theory analyses including the interface energy, charge density differences, and orbital hybridization: Cu, Mg, and Zn atoms could stabilize the Al/TiC(111) interface, whereas Mn and Si atoms promoted the rapid growing and disappearance of the TiC(111) planes in the Al melt. This work provides a feasible way to intelligently design and manipulate TiC nanoparticles with desirable exposed crystal planes, and exhibits a promising prospect for personalized applications.

Role of homogeneous distribution of SiC reinforcement on the characteristics of stir casted Al–SiC composites

Stir casting process is very popular for the fabrication of particle reinforced metal matrix composites. However, achieving a homogenous distribution of the reinforcement particles is very challenging, which directly affect the final mechanical performances. In this research, a detailed investigation was conducted to obtain a superior synthesis of Al–SiC composite materials and to detect the effect of SiC particles distribution on the mechanical characteristic of the stir casted Al matrix composites using glycerol–water based model. The glycerol–water based model study displays the impacts of viscosity of Al melt (1.04–1.24 mPa.s), impeller position (10–50%), stirring speed (100–300 rpm) and blade angle (0–90°) on the vortex height, dispersion time, settling time and clustering of particles. The results of the experiments using glycerol–water based model, 45° blade angles, impeller position of 40% from the base, stirring speed of 250 rpm showed the best uniform distribution of reinforcement particles. Confirmation experiments were carried out by fabricating Al–SiC PRMMC based on three different viscosities (1.04, 1.13, and 1.24 mPa.s) of Al melt and considering other parameters as constant. Fabricated Al–SiC samples were analysed by Scanning Electron Microscope (SEM) and mechanical testing such as tensile, hardness and wear tests. Based on the confirmation results, the viscosity of 1.13 mPa.s for Al melt (at 750 °C) resulted in uniform distribution of SiC particles, which enhanced the tensile strength by 4%, wear resistance by 21%, and led to a uniform hardness value of 47 VHN throughout the composites.

Bonding of compound casted Ti/Al bimetal by heat treatment

The formation mechanism of the bonding between compound cast Al/Ti bimetal during a heat treatment regime was investigated. Commercially pure Al was cast and melt on a Ti bar in a steel tube, followed by heat treatment on the compound cast Ti/Al bimetal for different periods of time once the Al melt was solidified. No bonding was observed between the two metals after the initial casting, which can be attributed to the presence of oxide films on the liquid Al and solid Ti alloys and the trapped atmosphere between them. The effect of these layers in preventing the formation of bonding was eliminated after heat treating the cast part at ∼973 K (∼700°C) for at least 15 min, and the metals started to bond with each other. A detailed description of this bonding mechanism is presented in this paper.

Influence of Mn and TiB<sub>2</sub> on the Microstructural Evolution of the Primary α-Al Grains and Fe Containing Intermetallic in the Wrought Al-Mg-Si Alloy

The most popular aluminium alloy used for the automotive applications is the wrought-Al alloy, where its popularity arises from its intrinsic characteristics such as, excellent formability, crash resistance, corrosion resistance and excellent specific strength. In the coming decades the use of aluminium alloys is expected to increase within automotive and aerospace industries, where this will source for an upsurge in Al recycling. Problems arise during Al recycling, where there is a steady build-up of Fe content, as this is recognised as being an impurity element. Fe has very little solubility in Al in its solid state and precipitation of these Fe intermetallics (IMC), in the Al matrix decrease mechanical properties, due to the Fe IMC brittle nature. These Fe-rich IMC also have very little cohesion to the Al matrix and can separate from the Al matrix resulting in the development of voids, where the initiation of microcracks becomes ostensible when subjected to thermomechanical processing. In order to curtail the damaging effect of the Fe IMC it so of importance to alter the nucleation and growth characteristic of the Fe rich IMC during solidification. Addition of trace elements and the manipulation of cooling rates have shown to be an effective technique to alter the Fe IMC morphology. In order observe the morphological evolution of the Fe IMC, various experiments were conducted using Al-1Si-1Mg-1Fe alloy with the addition of Mn and TiB2-based commercial grain refiner. Microstructural analysis of the primary α-Al and Fe IMC are observed and the morphological evolution of the Fe IMC is analysed with respects to the addition of Mn and TiB2. How the addition of these trace elements influence the growth characteristics and chemistry of the Al melt is also presented in this work.