Molten Aluminum Alloy Research Articles

Microstructure evolution, mechanical properties, and fractography of AA7068/ Si3N4 nanocomposite fabricated thorough ultrasonic-assisted stir casting advanced with bottom pouring technique

Ceramic particulate embedded aluminum metal matrix nanocomposites (AMNCs) possess superior mechanical and surface properties and lightweight features. AMNCs are a suitable replacement of traditional material, i.e., steel, to make automotive parts. The current work deals with developing Si3N4 strengthened high strength AA7068 nanocomposites via novel ultrasonic-assisted stir casting method advanced with bottom pouring setup in the proportion of 0.5, 1.0, 1.5, and 2 wt.%. Planetary ball milling was performed on a mixture of AA7068 powder and Si3N4 (in the proportion of 3:1) before incorporation in aluminum alloy melt to avoid rejection of fine particles. Finite element scanning electron microscope (FESEM), Energy dispersive spectroscopy (EDS), X-Ray diffraction (XRD), and Elemental mapping techniques were used in the microstructural investigation. Significant grain refinement was observed with increasing reinforcing content, whereas agglomeration was found at higher weight %. Hardness, Tensile strength, ductility, porosity content, compressive strength, and impact energy were also examined of pure alloy and each composite. Improvement of 72.71%, 50.07%, and 27.41 % was noticed in hardness value, tensile strength, and compressive strength, respectively, at 1.5 weight % compared to base alloy because of various strengthening mechanisms. These properties are decreased at 2 wt.% due to severe agglomeration. In contrast, nanocomposite’s ductility and impact strength continuously decrease compared to monolithic AA7068. Fracture analysis shows the ductile and mixed failure mode in alloy and nanocomposites.

Erosion Resistance of Heat-treated Aluminum Cast Iron to Aluminum Alloy Melt

Erosion Resistance of Heat-treated Aluminum Cast Iron to Aluminum Alloy Melt

Effect of ultrasonic field on the microstructure and mechanical properties of sand-casting AlSi7Mg0.3 alloy

Abstract The injection of ultrasonic wave into a melt during casting can refine grain size, improve grain distribution, and thereby enhance casting performance. The available studies on ultrasonic-assisted casting are mostly about inserting a transducer directly into the melt. Such a method is not suitable for sand casting. Therefore, the study of ultrasonic sand casting by indirectly injecting ultrasonic waves into an aluminum alloy melt through a sand mold was proposed and carried out in this study. The effects of ultrasonic waves of different powers at different solidification stages on the microstructure and mechanical properties of the melt were studied. Compared to conventional sand casting, the samples prepared by ultrasonic sand casting have finer grains and better grain distribution, as well as higher mechanical properties. Moreover, the sample’s performance improves to different levels when the same ultrasonic wave is injected at different periods, when compared to the injection of ultrasonic waves with different powers in the same period.

Ultrasonically Stir Cast SiO2/A356 Metal Matrix Nanocomposites

Metal matrix nanocomposites are a newly developed materials with promising applications in a wide variety of areas, ranging from medical to aerospace structures, owing to their lightweight high-strength properties. A light metal like aluminum is usually strengthened by a reinforcing agent of carbides, nitrides, oxides, carbon-based materials, or even elementals to boost the mechanical performance without sacrificing lightweight; however, almost all reinforcing nanomaterials are commonly poorly wetted by metals leading to agglomerations, clusterings, among other problems, with diminished ductility and overall mechanical performance. To tackle the mentioned problems, a number of strategies including coatings, thermal, mechanical, or chemical treatments may be followed. In the present study, a particular focus is paid on the mechanical dispersion of nano-silica particles in a molten A356 alloy through applying high-intensity ultrasonic agitations in order to improve dispersibility, wettability, and interfacial affinity. Nano-silica being an inexpensive high-strength nanomaterial is added to an A356 aluminum alloy melt and then dispersed and distributed by a 2-kW power ultrasonic system. Experimental results including microscopic observations and those mechanical experimentations revealed that the ultrasonication of the aforesaid solid–liquid system may greatly improve the affinity between the de-agglomerated nano-silica particles and the host aluminum matrix with enhanced ductility.

On the interactions between molten aluminum and high entropy alloy particles during aluminum matrix composite processing

The feasibility of adding AlCrTiV high entropy alloy (HEA) particles to molten aluminum to make metal matrix composites was studied. Equiatomic AlCrTiV HEA particles, produced by a solid state reduction process, were dispersed into pure aluminum and 7075 alloy (Al-5.8Zn-2.3Mg-1.4Cu, all weight %) melt and by a ultrasonic dispenser. It was found that the AlCrTiV particles reacted with molten aluminum, leading to the formation of Al45(Cr,V)7 and Al3Ti intermetallic phases in the aluminum matrix composites. Although the AlCrTiV HEA particles did not survive in molten aluminum during composite processing, the final composite materials showed significantly improved mechanical properties, due to grain refinement and dispersion strengthening. The research suggests that the interactions between matrix aluminum alloys and the particles are key in controlling the final microstructure and properties of the composites.

Interfacial behaviors and joint properties of the dual beam laser fusion brazing Ti6Al4V/AA7075 dissimilar metals

The AA7075 aluminum alloy with Ti6Al4V titanium alloy in lap configuration was successfully joined with laser fusion brazing method without filler wire. The effects of laser fusion brazing parameters, including defocus distance and laser power, on the joint appearance, interfacial microstructure and mechanical properties of the joints were explored. The results indicated that a good joint appearance could be obtained with variation of defocus distances. The adjustable range of laser power was expanded with the increase of defocus distance, from the range of 1600-1800 W with the laser spot diameter of 1.0 mm (defocus distance of +10 mm) to 2600 W–3400 W with the laser spot diameter of 2.7 mm (defocus distance of +20 mm). It was observed that the wettability of molten aluminum alloy on titanium alloy was improved with the increase of laser power, the wetting length was increased from 1.76 mm to 3.62 mm and the contact angle was decreased from 32.8° to 21.6° upon increasing the total laser power from 2400 W to 3000 W with the defocus distance of +15 mm. There was a continuous 0.7 ± 0.2 μm thick TiAl3 IMC (intermetallic compound) layer at the brazing interface with the defocus distance of +15 mm and laser power of 3000 W. The tensile strength and fracture location of the joints were mainly dependent on the spreadability and IMC thickness along the interface. Poor spreadability and too thick IMC thickness at the inner part of interface will result in fracture along the Al/Ti interface and lower strength. The best mechanical properties of the joints with the fracture load of 3621 N on average could be obtained with the defocus distance of +20 mm and laser power of 3400 W.

Effect of Sc on the Hot Cracking Properties of 7xxx Aluminum Alloy and the Microstructure of Squeeze Castings.

In this paper, the effect of adding the refiner Sc to the high Zn/Mg ratio 7xxx series aluminum alloy melt on the hot tearing performance, microstructure, and mechanical properties of the alloy is studied. The hot tearing performance test (CRC) method is used to evaluate the hot tearing performance of the alloy. The squeeze casting process was used to form solid cylindrical parts to analyze the structure and properties of the alloy. This study shows that the hot cracking sensitivity of the alloy after the addition of the refiner Sc is significantly reduced. The ingot grain size is significantly reduced, and the average grain size is reduced from about 86 μm to about 53 μm. While the mechanical properties are significantly improved, and the tensile strength reduced from 552 MPa is increased to 571 MPa, and the elongation rate is increased from 11% to 14%.

A study on microstructure and mechanical behaviour of AA6063 metal matrix composite reinforced with areca sheath ash (ASA) and rice husk ash (RHA)

Now a day’s composite materials can also prepared with the addition of agricultural by products ash as a reinforcement which gives an effective result. The Rice Husk Ash (RHA) and Areca Sheath Ash (ASA) ranged from 0% to 8 % increased by 2% with the molten aluminium alloy individually using stir cast route hence evaluate performance of reinforcement. Microstructural characterization and mechanical properties have been used to evaluate the performance of the composites. SEM and EDS analyses were analysed for microstructure characterizations of composites. In this paper Hardness, Tensile strength, Compression strength properties were investigated. Results obtained from experiments that the hardness, compression strength and tensile strength of the composites increased with an increase in the weight percentage of Rice husk ash (RHA) and Areca sheath ash (ASA).From the results Areca sheath ash can also used as a alternative reinforcement which leads to increase properties of composites.

Numerical investigation on flow process of liquid metals in melt delivery nozzle during gas atomization process for fine metal powder production

Based on volume of fluid (VoF) interface capturing method and shear-stress transport (SST) k-ω turbulence model, numerical simulation was performed to reveal the flow mechanism of metal melts in melt delivery nozzle (MDN) during gas atomization (GA) process. The experimental validation indicated that the numerical models could give a reasonable prediction on the melt flow process in the MDN. With the decrease of the MDN inner-diameter, the melt flow resistance increased for both molten aluminum and iron, especially achieving an order of 102 kPa in the case of the MDN inner-diameter ≤1 mm. Based on the conventional GA process, the positive pressure was imposed on the viscous aluminum alloy melt to overcome its flow resistance in the MDN, thus producing powders under different MDN inner-diameters. When the MDN inner-diameter was reduced from 4 to 2 mm, the yield of fine powder (<150 μm) soared from 54.7% to 94.2%. The surface quality of powders has also been improved when using a smaller inner-diameter MDN.

A Calculation Model for Cooling Rate of Aluminum Alloy Melts during Continuous Rheo-Extrusion.

The melt temperature of aluminum alloys plays a significant role in determining the microstructure characteristic during continuous rheo-extrusion. However, it is difficult to measure the actual melt temperature in the roll-shoe gap. In this work, based on the basic theory of heat transfer, a calculation model for heat transfer coefficient of cooling water/roll interface and melt/roll interface is established. In addition, the relationship between the temperature at the melt/roll interface and the velocity of cooling water is investigated. Combined with the CALPHAD calculation, the melt temperature during solidification in the continuous rheo-extrusion process is calculated. Using this model, the cooling rate of an Al–6Mg (wt.%) alloy melt prepared by continuous rheo-extrusion is estimated to be 10.3 K/s. This model used to determine the melt parameters during solidification provides a reference for optimizing the production process of continuous rheo-extrusion technology.

Aluminium foam with sub-mm sized cells produced using a rotating gas injector

Closed-cell solid aluminium alloy foams should ideally contain small and equally sized cells for the sake of better and more predictable mechanical properties, but real foams generated by injection of gas into melts usually exhibit a broad distribution of cell sizes and shapes. Here we investigate how gas bubbles in an aluminium alloy melt containing stabilizing SiC particles can be created in a controlled way by letting the injector move on a circular orbit through the melt at different velocities and adapting the gas flow. The structures of the resulting solidified foams are characterized by X-ray tomography. We identify conditions that allow us to obtain near-monodisperse foams with cell sizes below 1 mm and are able to reduce the content of SiC particles from the usual 20 vol% to 8 vol%.

Surface energy contributions to the work of infiltration in metal matrix composite processing

The work needed to mechanically drive molten metal into a porous solid preform when producing a composite material by infiltration can significantly exceed the energy change required for thermodynamically reversible infiltration. We measure, by quantitative metallographic analysis of partially infiltrated, particle- or fiber-based non-metallic preforms, the evolution with saturation of the three interfaces present during the process. Results show that irreversible energy losses in the infiltration of alumina preforms by molten copper, aluminium or aluminium-tin alloy cannot be ascribed to the creation of liquid meniscus surface area at intermediate metal saturation. This result agrees with similar observations in soil science and gives experimental confirmation of predictions from a recent simulation of capillarity-dominated metal infiltration [Acta Mater., vol. 210, 2021, 116831].

Microstructure and mechanical properties of 6082-T6 aluminum alloy–zinc coated steel braze-welded joints

Abstract The laser braze-welding technique was aimed to join a low alloyed zinc coated steel used in automotive industry, with a deformable, aging hardenable aluminum alloy from the 6xxx series using as filler material a AlSi12 wire. The heterogeneous joint was obtained by welding of aluminum alloy with the filler wire and by brazing of molten aluminum alloy together with the filler wire on the surface of a zinc coated steel which remained in solid state. The results showed that by using a proper heat input, the zinc coated steel was brazed without a melting process by the aluminum alloy which was in liquid state. On the interface between the zinc coated steel and the welded seam, a thin layer (the thickness was 6 to 8 μm) formed consisting of star (Al-Fe-Si) or needle shape (Mg-Al-Fe-Mn) intermetallic phases.

Investigation on corrosion mechanism of stirring paddles of different iron-based materials in ZL101 aluminum melt

Aiming at the material selection of the stirring paddle in the mechanical stirring equipment, the corrosion mechanism of four different iron-based material stirring paddles when stirring the ZL101 aluminum alloy melt were studied. Using scanning electron microscopy (SEM), EDS and OM methods, the microstructures and phase compositions of the reaction layers formed by the corrosion of the ZL101 melt in the four iron-based stirring paddles of A3 steel, heat-resistant stainless steel 1.4837, QT5381 and HT300 during the stirring process were analyzed. The experimental results show that the microstructures and phase compositions of the reaction layers of the A3 steel, QT5381, HT300 had certain similarities, and the heat-resistant stainless steel 1.4837 showed greater differences due to the presence of alloy elements such as Cr and Ni. The comparison indicated that due to the presence of flake graphite, the HT300 hindered the corrosion of the aluminum alloy melt on the substrate, which has the best corrosion resistance. Furthermore, the corrosion mechanism of the aluminum alloy melt on different stirring paddles were also analyzed. During the stirring process, the liquid aluminum and iron-based stirring paddle infiltrated, dissolved, and adsorbed each other. Due to the reaction and diffusion of the aluminum and iron atoms, the Fe–Al intermetallic compound layer was gradually formed at the interface of the iron-based material and aluminum melt, and the presence of Si, Cr and other elements leaded to the formation of more complex intermetallic compounds.

Corrosion and thermal fatigue behaviors of induction-clad Ni-coated TiC particle-reinforced Ni60 coating in molten aluminum alloy

The Ni60 coatings were fabricated via induction cladding with Ni-coated TiC reinforcement particles using electroless plating to improve the coating quality. The corrosion and thermal fatigue behaviors of the H13, Ni60 coating and Ni-coated TiC particle-reinforced Ni60 coating in molten aluminum alloy were investigated. The results showed that Ni-coated TiC by electroless plating significantly improved preparation quality of ceramic particle-reinforced Ni60 coating. The weight loss of the received coating in molten aluminum alloy was about 25% of that of the H13 and 66% of that of the Ni60 coating. The corrosive mechanisms of the H13 steel and Ni60 coating in molten aluminum alloy involve the matrix phase Fe and Ni60 alloy being corroded by aluminum to form M-Al(M = Fe,Cr) intermetallic compounds (IMCs) and M-Al (M = Ni, Fe, Cr) IMCs, respectively. The corroded surface of the H13 steel showed flaky exfoliation happened at the Fe-(Fe,Cr) 2 Al 5 interface, while that of the Ni60 coating presented some large-scale cotton-like morphology due to fracture occurring at the Al-(Ni,Fe,Cr)Al 3 interface. The addition of the Ni-coated TiC particles effectively reduced further dissolution of Fe, Cr and Ni of the received coating into molten aluminum alloy, and changed interface morphology of Al-(Ni,Fe,Cr)Al 3 interface from cotton like to little serrate like, and significantly enhance the corrosive resistance to molten aluminum alloy. The thermal fatigue failure mode of the H13 steel is mainly surface oxidation and lamellar spalling of the oxide layer, and the thermal fatigue cracks of the Ni60 coating initiated in the oxide layer of M-Al (M = Ni, Fe, Cr) IMCs and propagated longitudinally under the action of thermal stress, while cracks of the Ni-coated TiC-reinforced Ni60 coating originated at the junction of non-eroded titanium carbide and eroded Ni60 alloy at the erosion front and propagated in the TiC particles and coating matrix phases. • Process combination of induction cladding and electroless plating • Induction-clad Ni60 coatings with Ni-coated TiC reinforcement particles using electroless plating • Significant improvement of preparation quality of TiC-reinforced Ni60 coating using electroless plating • Corrosion and thermal fatigue behaviors of H13, Ni60 coating and Ni-coated TiC-Ni60 coating in molten aluminium alloy

Influence of Rare Earth and Fe Addition on the Microstructure and Mechanical Properties of Al-B Alloy

In this study, changes in the microstructure, mechanical properties, and electrical conductivity of as-cast and as-extruded Al–B based alloys with the addition of Fe and rare earth (RE) were investigated. The melted aluminum alloy was maintained at 750 °C and then poured into a mould at 200 °C. Aluminum alloys were hot-extruded into a rod that was 12 mm in thickness with a reduction ratio of 39:1. The addition of Fe and RE resulted in the formation of Al11RE3 and Al3Fe intermetallic compounds and the area fraction of these inter-metallic compounds increased with increasing Fe and RE contents. As the amount of Fe and RE increased, the average grain size of the extruded Al alloy decreased to 798.6, 196.1, and 21.9 µm, and the high-angle grain boundaries fraction increased to 24.8, 27.9, and 60.7%. In the case of cast materials, low electrical conductivity was shown by porosity and fine casting defects. As the Fe and RE contents increased, the electrical conductivity of the extruded Al–B alloy decreased to 62.3, 59.6 and 55.0% International Annealed Copper Standard. As the Fe and RE content increased the ultimate tensile strength improved from 90.8 to 112.9 MPa which was attributed to the grain refinement and formation of Al11RE3 and Al3Fe intermetallic compounds by the addition of Fe and RE.

Microstructures and Properties of V-Modified A380 Aluminum Alloy Produced by High Pressure Rheo-Squeeze Casting with Compound Field Treatment

The melt of V-modified A380 alloy aluminum alloy was treated by compound field of ultrasonic vibration (UV) and electromagnetic stirring (ES) around liquidus temperatures. Then the high pressure rheo-squeeze casting (HPRSC) process was used to produce an ingot with the alloy melt obtained. The results indicate that the polygonal Si2V phase is precipitated after adding vanadium to the alloy. With the increasing of V content from 0 to 1.05%, the average length and volume fraction of β-Al5FeSi phase is decreased to 30 μm and 1.44%, respectively. The refinement effects of UV, ES, and UV-ES compound field on the microstructure of the gravity casting alloy are as follows: UV-ES &gt; UV &gt; ES. When the pressure is increased from 0 to 400 MPa, the size of primary α-Al is decreased gradually, the morphology of β-Al5FeSi phase is changed from an acicular to a fine fibrous-like one, and the polygonal Si2V phase is refined to fine particle with an average grain diameter of about 8 μm. The ultimate tensile strength (UTS), yield strength (YS), and elongation of the alloy without V are lower than that of the alloy with 0.7% V under the same pressure. When the pressure is 400 MPa, the UTS, YS, and elongation of T6 heat-treated HPRSC alloy with 0.7% V are 301 MPa, 182 MPa, and 3.3%, respectively. With the decrease in the length of β-Al5FeSi phase, the quality index of the HPRSC alloy is increased.

An investigation of semisolid Al7075 feedstock billet produced by a gas-assisted direct thermal method

Semisolid metal (SSM) processing is a forming process which occurs within solidus and liquidus temperatures, and it requires feedstock billets with spheroidal microstructures. In this paper, a novel gas-assisted direct thermal method (DTM) is proposed as a method to create feedstock billets with fine spheroidal microstructures. Effect of different combination parameters between pouring temperature and holding time during the gas-assisted DTM technique on the microstructure of aluminium alloy 7075 feedstock billets was investigated. Pouring of molten aluminium alloy 7075 was conducted at temperatures between 645 and 685 °C, while holding time was set between 20 and 60 s. The melt was cooled down within the semisolid temperature range in a cylindrical copper mould with the help of carbon dioxide (CO2) gas before quenching in room temperature water. Results revealed that the smallest primary phase grain size formed at the combination parameters of 645 °C pouring temperature and 20-s holding time. Furthermore, the same combination parameters also produced the highest circularity value. The addition of external CO2 gas surrounded the copper mould as a rapid cooling agent was found to have a significant improvement of 36.4% to the formation of smaller primary grain and spheroidal structure. It is concluded that the lowest pouring temperature and shortest holding time coupled with rapid cooling condition from the addition of external CO2 during DTM produced the finest and most globular structure of primary phase size.

A Simple Method for a Protective Coating on Stainless Steel against Molten Aluminum Alloy Comprising Polymer-Derived Ceramics, Oxides and Refractory Ceramics.

A new coating based on polymer-derived ceramics (PDC), oxides and refractory ceramic with a thickness of around 50 µm has been developed to improve the resistance corrosion of stainless steel substrate against molten aluminum alloy in a thermal energy storage (TES) system designed to run at high temperature (up to 600 °C). These coatings implemented by straightforward methods, like tape casting or paintbrush, were coated on planar and cylindrical stainless-steel substrates, pyrolyzed at 700 °C before being plunged for 600 and 1200 h in molten AlSi12 at 700 °C. The stainless-steel substrate appears healthy without intermetallic compounds, characteristic of molten aluminum alloy corrosion. The protective coating against AlSi12 corrosion shows excellent performance and appears interesting for TES applications.

Improved degassing efficiency and mechanical properties of A356 aluminium alloy castings by high shear melt conditioning (HSMC) technology

• Faster hydrogen removal technology than conventional rotary degassing methods. • Effective elimination of oxide bi-films by innovative rotor-stator design. • High technology efficiency as very low gas flow and rotor speed required. • No covering flux required to maintain good melt quality for long periods after degassing. • Improved casting integrity and mechanical properties due to enhanced melt quality. The degassing of aluminium alloy melts is a crucial step in the production of high-quality casting products, as the presence of dissolved hydrogen and oxide bi-films is detrimental to the mechanical properties. Current rotary degassing techniques are effective, but they lack efficiency because of the high gas flow and long processing times required. This study aims to solve this problem by presenting an innovative rotor-stator degassing technology, that combines controlled inert gas injection with intensive melt shearing. It has been applied to the liquid metal treatment of an aluminium cast alloy to evaluate the effect on melt cleanliness, casting integrity and mechanical properties. The optimum conditions for an efficient bubble dispersion have been obtained by water modelling. The melt quality during and after degassing has been assessed by in-situ measurement of hydrogen concentration and by reduced pressure test sampling for oxide bi-films and porosity content evaluation. This new technology is faster, requires less gas flow consumption and produces higher melt quality than the existing degassing techniques, due to a characteristic combination of distributive and dispersive mixing flow. In addition, re-gassing is minimised, maintaining a high melt quality for longer time after processing. This results in castings with less defects and better mechanical properties. The improved degassing efficiency of this technology makes it an excellent alternative in industry to increase melt quality and casting productivity.