Al Dendrites Research Articles

Microstructure and creep properties of cast near-eutectic Al–Ce–Ni alloys

This study investigates the as-cast and aged microstructures, thermal stability, ambient temperature strengthening, and creep resistance of three ternary Al–Ce–Ni alloys (wt%): near-eutectic Al–10Ce–5Ni (with both eutectic and hypoeutectic regions), hypoeutectic Al-7.5Ce-3.75Ni (with numerous primary Al dendrites), and hypereutectic Al-12.5Ce-6.25Ni (with coarse, blocky primary Al3Ni and Al11Ce3 precipitates and some primary Al dendrites). Depending on the alloy composition and local solidification conditions, the following eutectic morphologies are found: (i) coarse Al–Ce eutectic colonies where Al11Ce3 is in the form of “Chinese script”, (ii) intermingled regions of binary Al–Ce and Al–Ni eutectic colonies, with finer Al3Ni and Al11Ce3 fibers, (iii) large ternary eutectic colonies, where the binary Al3Ni and Al11Ce3 phases are alternating or intertwining within the individual, fine fibers (diameters of ∼60–170 nm, depending on solidification rates), and (iv) ternary eutectic zones (between primary Al dendrites), where fine Al3Ni and Al11Ce3 build up a 3D-interconnected network. The high volume fraction of intermetallic phases and extremely fine eutectic spacing/fiber diameter both contribute to high ambient strengthening (higher as-cast microhardness than binary Al–Ce or Al–Ni), and also provide enhanced creep resistance at 300 and 350 °C. The alloys are coarsening-resistant up to 425 °C for extended periods, with a gradual decrease in microhardness. The alloys aged at 400 °C to 1050 h show fiber fragmentation and coarsening of the resulting particles, with the faster-diffusing Ni driving more rapid coarsening of the Al3Ni particles which engulf finer, more stable Al11Ce3 particles. Severe overaging (performed at 590 °C for 24 h) leads to Al3Ni and Al11Ce3 spheroids which remain submicron-sized in eutectic colonies, but micron-sized at colony boundary and at Al dendrite-eutectic interface. Creep resistance at 300 °C of overaged Al–10Ce–5Ni remains substantial, consistent with load-transfer based composite strengthening being an important strengthening mechanism in these alloys, making them excellent candidates for replacement of heavier steel or titanium parts operating under stress up to 300 °C.

The Structure of Al – Mg – Si Casting alloys Modified by Lithium and Scandium

The structure of hypoeutectic Al – Mg – Si alloys cast in permanent mold, as well as using a high-pressure die-casting unit (HPDC), was investigated. Changes in the structure after additional alloying of the base alloy (Al – 5.5Mg – 2.5Si – 0.6Mn) with lithium and scandium were studied. For a more detailed description of the structure of the alloys, phase diagrams and the volume fractions of the phases in the Thermo-Calc software were calculated. Thermo-Calc results are in good agreement with metallographic studies. The microstructure of the alloys was investigated using a scanning electron microscope (SEM) on polished and deeply etched microsections. The article also shows the strong influence of the crystallization rate on the eutectic morphology and the secondary dendrite arm spacing (SDAS). Alloying the base alloy with lithium leads to a change in the eutectic morphology from lamellar to fine fibrous. Alloying with scandium not only changes the eutectic morphology from lamellar to the fine fibrous but also reduces the SDAS. Scandium addition leads to the formation of primary Al3Sc crystals, which act as a substrate for the heterogeneous nucleation of α-Al dendrites and Al – Mg2Si eutectic. To determine the effect of alloying elements on the properties of alloys, hardness, tensile strength, and elongation were measured. Local mechanical properties were measured as microhardness of α-Al dendrites, Al – Mg2Si eutectic, and Al3Sc phase. Alloys with lithium and scandium show increased properties in the cast state compared to the base alloy.

Stable and low-voltage-hysteresis zinc negative electrode promoting aluminum dual-ion batteries

Compared with the widely developed positive electrodes, the research on the high stability negative electrodes is far from in-depth in nonaqueous Al batteries. In order to fundamentally solve these key problems, including Al dendrites, corrosion and pulverization, it is urgent to develop an alternative stable negative electrode. Herein, the corrosion-resistant, low-voltage-hysteresis and stable Zn is demonstrated as a promising negative electrode. Since the deposited Al particles on the Zn electrode are prior to Zn in the stripping reaction, Zn electrode can remain good structural integrality, thus presenting great cycling stability and corrosion resistance. Importantly, the results in Al-Zn symmetric cells indicate that Zn possesses the ultra-low voltage hysteresis (∼17 mV at 0.5 mA cm−2), superior cycling stability (800 cycles at 1.0 mA cm−2) and Al plating/stripping reversibility characteristics. Additionally, the Zn-graphite full battery based on Zn as negative electrode and flake graphite as positive electrode delivers stable discharge capacity of 81.1 mAh g−1 over 300 cycles. The results in this work open an effective approach for constructing corrosion-resistant, low-voltage-hysteresis and stable negative electrode, further indicating that Zn is great promising as negative electrode for Al dual-ion batteries.

Tension-compression mechanical behavior and corresponding microstructure evolution of cast A356-T6 aluminum alloy

It is crucial to clarify the intrinsic deformation and damage behaviors of casting materials under different loading conditions for establishing the material damage model and accurately predicting the security performance of cast components. In this study, uniaxial tensile and compressive tests were performed to investigate the complete mechanical behavior of cast A356-T6 aluminum alloy at room temperature, and the corresponding microstructure evolution were analyzed. The tensile and compressive specimens were prepared at porosity-free locations on a low pressure die cast A356 wheel subjected to T6 heat treatment to avoid premature fracture caused by initial cast pores. The results show that negligible asymmetry in yielding and hardening behaviors is observed between tension and compression, but obvious differences in ductility exhibit. Specifically, the elongation for tension is limited to 15%, but reaches over a strain of 1.2 for compression. Additionally, microcracks during tension are prone to be initiated at the interface between Si and Al matrix, which mainly propagates in the Al dendrites, and finally leads to the fracture. While the dominant strain accommodated mechanism shifts with strain levels in compression. It evolves from the incipient plastic deformation inside grains at initial strain stage to the sliding of fragmented dendrite assisted by eutectic silicon particles at later stage, which may be the main reason for the superior ductility during compression.

MCD Approach for Assessing the Optimal Operating Condition during Sliding Wear Characteristics of LM25/SiC AMCs Processed by an Improved Stir Casting Technique

The Sliding wear behaviour of the improved stir cast LM25/SiC composite was investigated using a wear apparatus having pin-on-disc configuration. The tests were conducted at varying sliding speed, applied load and sliding distance based on the ‘Box-Behnken’ experimental design approach of Response Surface Methodology. The influence of process variables on wear rates, frictional heating and friction coefficient were analyzed by developing the regression model for the performance measures using RSM. The microstructural occurrences depicted strong interfacial bonding between the SiC particles and the matrix alloys due to entrapping of the SiC particles inside the primary Al dendrites. The Analysis of Variance (ANOVA) demonstrating the significance of each process variables on the developed regression model for all the performance characteristics. The linear and non-linear interaction effects of the process variables on the response measures were also identified using surface plots, further validated by experimental observations. A combined setting of process variables was identified, which thresholds the optimum values of combined performance measures using desirability based MOP. The confirmation experiments demonstrated that the errors were minimal (Wear rates 5.2%, 2.02% for frictional heating and 7.18% for COF) and fitted appropriately with developed quadratic surfaces for the response variables. The optimal processing condition was identified as Wear rate = 2.33 mm3/m; Temperature = 47 °C and COF = 0.167. The resulting surface was threshold a ‘Ra’ value of 1.66 μm, which was found to be lesser than that of the (Ra = 2.35 μm) surface produced during testing at initial parameter settings.

Al-Si 及びAl-Cu二元系合金の凝固及び冷却過程におけるα-Al デンドライト中の溶質分布

Al-Si 及びAl-Cu二元系合金の凝固及び冷却過程におけるα-Al デンドライト中の溶質分布

The effect of pouring temperature on the tensile strength and micro structure of Al alloys by centrifugal casting

There are many ways to overcome the leaking pipes in pipe joining; one of them is by using centrifugal casting as method for its production. The goal of this study is to know the effect of pouring temperature on the tensile strength and microstructure of centrifugal casted pipe product. We tried to produce the pipe at temperature of 680°C, 700°C and 720°C, with the constant rotation speed of the centrifugal casting machine (1500 rpm). The tensile test was done based on standard of ASTM E8. The results show that the highest tensile strength is obtained from the product that was manufactured at 680°C (136.3 MPa) and the lowest is at 720°C (115.3 MPa). These data are supported with the result of microstructure test which revealed that the amount of Al dendrite structure is more homogenous and uniform when the pouring temperature is closed to melting point.

Comparison of dynamic mechanical properties of non-superheated and superheated A357 alloys

The influence of superheat treatment on the microstructure and dynamic mechanical properties of A357 alloys has been investigated. The study of microstructure was performed by the optical microscope. Dynamic mechanical properties (storage modulus, loss modulus, and damping capacity) were measured by the dynamic mechanical analyzer (DMA). Microstructure showed coarser and angular eutectic Si particles with larger {\alpha}-Al dendrites in the non-superheated A357 alloy. In contrast, finer and rounded eutectic Si particles together with smaller and preferred oriented {\alpha}-Al dendrites have been observed in the superheated A357 alloy. Dynamic mechanical properties showed an increasing trend of loss modulus and damping capacity meanwhile a decreasing trend of storage modulus at elevated temperatures for superheated and non-superheated A357 alloys. The high damping capacity of superheated A357 has been ascribed to the grain boundary damping at elevated temperatures.

Dendrite-free Al recycling via electrodeposition using ionic liquid electrolytes: The effects of deposition temperature and cathode surface roughness

In this paper, the electrodeposition of Al from aluminum scrap alloys (A2020) on copper cathode substrates with varied surface roughness under different deposition temperatures was studied using low-temperature AlCl3-1-butyl-3-methyl-imidazolium chloride (BMIC) ionic liquid electrolytes. The bulk electrodeposition of Al was carried out under a voltage of 1.5 V at a stirring rate of 120 rpm using a fixed ionic liquid electrolyte concentration (molar ratio AlCl3: BMIC = 2:1). The effects of deposition temperature (range from 80 °C to 140 °C) and surface roughness of Cu cathode substrates (polished by 320, 600, 800, 1200 grits SiC sandpapers and mirror polishing process) on the morphology of deposited Al, current density, current efficiency and energy consumption, were investigated. The Al deposits were characterized using scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), profilometer, and electrochemical measurements for current density, current efficiency, and energy consumption. It is demonstrated that the deposition temperature and surface roughness of Cu electrodes play a critical role in the nucleation and growth of Al deposits. Higher deposition temperature promotes the diffusion and/or migration of Al2Cl7− ions and then enhances the current density and efficiency during the electrodeposition of Al. Smoother surface of Cu electrodes is preferred for the formation of dendrite-free Al deposits. Typically, on the mirror polished Cu electrode, no Al dendrite structure was observed, and only plate-like Al deposits were formed at the deposition temperature of 100 °C. Pure metallic Al was successfully deposited on Cu electrodes in AlCl3+BMIC ionic liquid electrolytes for all experiments with a current efficiency range from 72% to 99% and energy consumption of 4.6–6.3 kW h/kg Al.

Al homogeneous deposition induced by N-containing functional groups for enhanced cycling stability of Al-ion battery negative electrode

Rechargeable Al-ion batteries (AIBs) are considered as one of the most fascinating energy storage systems due to abundant Al resource and low cost. However, the cycling stability is subjected to critical problems for using Al foil as negative electrode, including Al dendrites, corrosion and pulverization. For addressing these problems, here a lightweight self-supporting N-doped carbon rod array (NCRA) is demonstrated for a long-life negative electrode in AIBs. Experimental analysis and first-principle calculations reveal the storage mechanism involving the induced deposition of N-containing function groups to Al as well as the ideal skeleton of the NCRA matrix for Al plating/stripping, which is favorable for regulating Al nucleation and suppressing dendrites growth. Compared with the Al foil, the NCRA exhibits lower areal mass density (∼ 72% of Al foil), smaller thickness (40% of Al foil), but much longer cycle life (> 4 times of Al foil). Benefiting from the remarkable stability of the array structure, symmetric cells show excellent cycling stability with small voltage hysteresis (∼ 80 mV) and meanwhile there are no corrosion and pulverization problems even after cycled for 120 hours. Besides, full cells also manifest long lifespan (1,500 cycles) and increased Coulombic efficiency (100±1%).

Suppressing Al dendrite growth towards a long-life Al-metal battery

Great progress has been made in the development of cathode materials for Al-metal batteries. However, the in-depth study of Al anodes, especially the battery instability caused by Al dendrite growth, has not received much attention. In this work, we have identified the in-situ formation of Al dendrite growth, which is proved to bottleneck the practical use of Al-metal batteries. The dendrite formation severely affects battery performance, such as voltage and efficiency fluctuations, unstable cycling, etc. To further demonstrate the detailed growing process of dendrites, we make a comprehensive investigation into the interfacial chemistry of Al anode. We have found that the naturally formed Al2O3 surface film is dissolved in the ionic liquid electrolyte during Al plating, accompanied by the formation of solid-electrolyte interphase containing Al-Cl and Al-O like species on the anode surface before dendrite growth. To suppress this dendrite growth, we propose the use of porous Al, which provides a homogeneous ion flux and decreases the local current density. As a result, the porous anode maintains stable cycling over a wide range of current densities and areal capacities. The Al-graphite battery shows stable cycling up to 18000 times without capacity decay. This work suggests the significance of suppressing dendrite growth for the real applications and commercialization of Al-metal batteries and will draw attention to the battery design from the anode side.

Analisis Perubahan Sifat Mekanik Al 6063 Setelah Dilakukan Heat Treatment Pada Temperatur Tetap Dengan Waktu Tahan Yang Bervariasi

Aluminium is a material commonly used in human activity. On operating condition, people expect that aluminium has mechanical properties such as hardness. The mechanical properties can be improved by doing some treatment processes, such as by heat treatment. Al alloys 6063 has a smaller strength than other alloys, but very lithe. Al alloys 6063 also has very good ability to forging, and can be strengthened by heat treatment after processing. AI alloys 6063 contains chemical compotition 98.7% Al, 0.530% Si and 0.532% Mg. AI alloys 6063 common used for frame construction, engine piston, cylinder head combustion engine, bicycle parts, etc, because alloys have excellent corrosion resistance properties than the other heated aluminium. In this research, Al 6063 will be heated on 530 ° C with variation holding time from 30 minutes to 60 minutes and then cooled by fresh air. Next, observing microstructure. Finally, from the research results found Al dendrite structure and spread particle of Si and the formation of particle enlargment. Heat treatment of Al 6063 doesn’t have big impact, heating process should be done with variation holding time over 60 minutes. Longer heating process will give higher hardness value or better.

In-situ 3D characterization of tensile damage mechanisms in A319 aluminium alloy using X-ray tomography and digital volume correlation

Tensile tests with 3D in-situ observation were performed using X-ray tomography on a solution heat treated Lost Foam Cast A319 alloy. In-situ tensile testing allowed crack initiation and propagation to be visualised in 3D whilst the digital volume correlation technique was used to measure 3D deformation fields. Crack initiation mechanisms and the evolution of damage during crack growth together with the localized strains at the onset of cracks were studied in 3D. The results show that cracks initiate at hard inclusions, i.e. eutectic Si, iron intermetallics and Al2Cu intermetallic phase, in the vicinity of large pores under the influence of their strain concentration. Once initiated, cracks appeared to preferentially grow through the cracked hard inclusions. Quantitative analysis revealed that the average strain level for the failure of iron-intermetallics exhibits lower value than for Al2Cu intermetallic phase. Besides, final fracture was more prone to occur at Si phase, iron intermetallics and Al2Cu intermetallic phases than Al dendrites. For the various hard inclusions, failure predominantly occurred by fracture rather than decohesion.

Effect of Scan Strategies and Use of Support Structures on Surface Quality and Hardness of L-PBF AlSi10Mg Parts.

Additive manufacturing allows for a great degree of design freedom and is rapidly becoming a mainstream manufacturing process. However, as in all manufacturing processes, it has its limitations and specificities. Equipping engineers with this knowledge allows for a higher degree of optimization, extracting the most out of this technology. Therefore, a specific part design was devised and created via L-PBF (Laser Powder Bed Fusion) using AlSi10Mg powder. Certain parameters were varied to identify the influence on material density, hardness, roughness, residual stress and microstructures. It was found that on heat treated parts laser pattern strategy is one of the most influential aspects, showing that chessboard and stripes 67° improved outcome; average Ra roughness varied between 8–12 µm, residual stress was higher on vertical surfaces than horizontal surfaces, with the combination of support structures and stripes 67° strategies generating the lowest residual stress (205 MPa on a lateral/vertical face), hardness was non-orientation dependent and larger on samples with chessboard fabrication strategies, while microstructures were composed of α–Al dendrites surrounded by Si particles. The distribution and grain size of the microstructure is dependent on location regarding melt pool and HAZ area. Furthermore, Al–Mg oxides were encountered on the surface, along with pores generating from lack of fusion.

Effects of microstructural heterogeneity on fatigue properties of cast aluminum alloys

Cast Al alloys are widely employed for engine components, structural parts, gear box, chassis, etc. and subjected to mechanical cyclic load during operation. The accurate fatigue life prediction of these alloys is essential for normal operation as fatigue cracks initiated during operation induce the lubrication oil leak and serious safety hazard. Microstructural heterogeneity, including shrinkage/gaspores and secondary phase particles, is the most detrimental factor that affects fatigue life of cast Al alloys. The approximate fatigue life cycles could be estimated based on the size distribution and locations of shrinkage pores/defects. The relationship between crack population and stress was reported by statistical distributions and the cumulative probability for cast Al alloys fail at a certain stress could be predicted by combination of Paris law and pore size distribution. Pore depth was found to dominate the stress field around the pore on the surface and the maximum stress increases sharply when the pore intercepted with the surface at its top. The microstructure of cast Al alloys usually is composed of primary Al dendrites, eutectic silicon, Fe-rich particles and other intermetallic particles are dependent upon alloy composition and heat treatment. The coalescence of microcracks initiated from the fractured secondary phases was clearly found and can accelerate the initiation and propagation of the fatigue cracks. A link between defect features and the fatigue strength needs to be established through a good understanding of the fatigue damage mechanisms associated with the microstructural features under specific loading conditions. This paper reviews the influences of shrinkage/gaspores and secondary phase particles, formed during casting process, on the fatigue life of Al-Si-Mg cast Al alloys.

Arc deposited AlSi12 cladding layer on steel plate without zinc coating

ABSTRACTAlSi12 cladding layer was fabricated on steel plate without zinc coating via cold metal transfer arc deposited technique. The wettability, morphologies, microstructures, and mechanical properties of the cladding layer were investigated. The cladding layer exhibited favourable wettability with steel plate. Large swing amplitude and high swing frequency were the key factors to achieve excellent wettability. The cladding layer was composed of primary Al dendrites and (Al + Si) eutectic structure, and the microstructures were refined. Continuous and thin intermetallic compound layer appeared at AlSi12/steel interface, and reliable bonding strength between the cladding layer and steel plate was achieved. The fracture surface exhibited both brittle fracture and ductile fracture.

Characterization of in Situ Zirconium Diboride (Zrb2) Reinforced by Aluminium-Copper (Al-Cu) Metal Matrix Composites

Aluminium matrix composites by way of in-situ reaction has arisen as a preference conducive to knock out imperfections and defects exiting within ex situ MMC. In the present work, Al-Cu-ZrB2 have been develop through in situ reaction which boost mechanical properties over dispersion strengthening together with grain refinement obtained by the existence of each particulates inside the melt all along solidification. Al-Cu reinforced among different proportion of ZrB2 (0, 3 and 6 wt. %) synthesized using in situ fabrication at 800 °C of molten aluminum-copper alloys by inorganic salts K2ZrF6 together with KBF4. The amalgam were specified using XRD, FESEM together with mechanical test on appropriately sectioned and metallographically prepared surface to examine and inspect phase distribution, hardness together with tensile properties. From result acquired, raised ZrB2 amount will increase rate of tensile and hardness characteristics of Al-Cu alloy. XRD patterns exposed development of ZrB2 particulates without existence of unspecified other compounds. Most of ZrB2 granular were located near grain boundaries of Al dendrites. Microstructural analysis exposed the homogeneous and consistent allocation of second phase particles, clean interface and favorable bonding. It is support that ZrB2 molecules are predominantly in nano size among hexagonal either tetragonal shape, yet minor molecules in micron size are also noticed. For that reason, composite synthesized using in situ techniques exhibit homogeneous distribution of reinforcing tend to be superlative associated within clean interface along the metallic matrix. In order to accomplish better mechanical features, it is necessary to regulate and control phase arrangement all along fabrication of Al-Cu with higher contents of ZrB2.

Ultrasonic-Assisted Laser Metal Deposition of the Al 4047Alloy

Ultrasonic-assisted laser metal deposition(UALMD) technology was used to fabricate Al 4047 parts. The effect of the powder feeding laser power, remelting laser power and ultrasonic power on the relative density of the parts was investigated. The relative density, microstructure and mechanical properties of the specimens obtained by the optimized process parameters were compared with the corresponding properties of the cast alloys. The results showed that dense alloys with a maximum density of 99.1% were prepared using ultrasonic vibration and by remelting the previously deposited layer with the optimized processing parameters, and its density was almost equivalent to that of the cast parts. The microstructure of the samples using optimal laser parameters presented columnar Al dendrites and equiaxed Si particles at the boundary of each deposited layer, while the supersaturated Al solid solution was transformed into equiaxed crystal surrounded by fine fibrous Si phases at the center of the layer. Moreover, the size of the primary Al and the Si particles in the samples produced by UALMD was remarkably refined compared to that of the primary Al and Si particles in the cast structure, resulting in grain refining strengthening. The observed variation in the microstructure had an obvious impact on the tensile properties. The mechanical behavior of the deposit obtained by UALMD revealed superior tensile strength, yield strength and tensile ductility values of 227 ± 3 MPa, 107 ± 4 MPa and 12.2 ± 1.4%, which were approximately 51%, 38% and 56% higher than those of the cast materials, respectively.

Microstructure evolution in an Al-Si piston alloy under ultrasonic melt processing

Piston Al-Si eutectic alloys are used to produce direct-chill cast billets for subsequent forging. Because of a very complex composition and multi-phase heterogeneous structure, it is necessary to control the formation of primary and eutectic compounds either through alloying or casting conditions (or both). In this study we used ultrasonic melt processing above or across the liquidus line to affect the occurrence and size distribution of primary Si as well as morphology of primary Al dendrites and high-temperature eutectic phases. The refinement of these particles has potential benefit for mechanical properties and formability during forging.

Influence of trace Zr on the microstructure and elevated temperature properties of an Al–Si–Cu–Ni–Mg piston alloy

The effect of trace Zr on the microstructure, precipitates and mechanical properties on an Al–12.6 wt% Si–4 wt% Cu–1.5 wt% Ni–1.5 wt% Mg piston alloy was studied in this paper. The α–Al dendrites are refined, resulting in a more compact distribution of primary intermetallics. The main precipitates are S (Al2CuMg) after T6 heat treatment. It was found that the S precipitates are denser and finer in the Zr–contained alloy whereas L12–ZrAl3 particles also precipitate. The hardness and elevated temperature tensile strength of the piston alloy were both improved, indicating the positive effect of trace Zr.