Al-Si Cast Alloys Research Articles

Development of Pore-Free Ti-Si-C MAX/Al-Si Composite Materials Manufactured by Squeeze Casting Infiltration

Open-porous MAX phase skeletons from Ti3SiC2 were manufactured by Microwave-Assisted Self-propagating High-temperature Synthesis (MASHS) and subsequently subjected to squeeze casting infiltration with an Al-Si lightweight casting alloy (EN AC-44200). This alloy was chosen due to its high flowability, corrosion resistance and good machinability. The manufactured composites, together with a reference sample of the original alloy, underwent testing of thermal properties, including thermal conductivity and diffusivity, specific heat and thermal expansion in the temperature range 50-500 °C, which corresponds to the expected working temperatures of the material. The fabricated AlSi/Ti3SiC2 composites have significantly increased thermal stability, with coefficients of thermal expansion (approximately 10-11 × 10−6 °C−1) half that of the original alloy. As regards mechanical properties, the instrumental Young’s modulus and Vickers hardness of the composite materials are 170.8 and 8.5 GPa, respectively. Moreover, the microstructure and phase composition, structural defects and potential impacts between constituents of the manufactured composites were characterized using SEM, TEM and STEM microscopy and EDS and XRD analysis.

Wear behaviour of cast aluminium silicon (Al-Si) alloy in Dot 4 brake fluid

The frictional sliding behaviour of cast Al-Si alloy was investigated with and without DOT 4 hydraulic brake fluid lubrication/environments. Cast Al-Si specimen was produced from wrought alloy and the specimen surface was metallurgically prepared. The as-cast product was characterized with aid of micro-hardness tester, the chemical composition was analysed by X-ray fluorescence (XRF), while X-ray diffraction (XRD) was used to identify phases present, microstructures and surface examinations were done on a high resolution metallurgical Optical Microscope. The properties of the polished and worn sample surfaces were examined by Scanning electron microscope (SEM) equipped with Energy dispersive X-ray (EDS) facilities. A 6mm diameter alumina ball under varying normal loads (3-10 N) was rubbed against the surface of the cast Al-Si coupon specimen. The dry and wet sliding wear behaviour was assessed based on the CoF-sliding time behaviour. From the results, the average CoF values of 0.9064 for dry and 0.2038 for wet contacts were obtained. Comparatively, 1.03E-06 and 4.21E-07 minimum wear intensities; and 467290 and 132170 wear resistances were obtained for dry and wet contacts respectively. Behaviour of cast Al-Si in DOT4 were compared with its performance in DOT3 regarding the hydraulic brake system application.

Effect of Grain Refiners and/or Modifiers on the Microstructure and Mechanical Properties of Al-Si Alloy (LM6)

Grain refinement is one of the most important and popular melt treatment process for Al-Si alloy casting. Microstructure and mechanical properties of commercially available Aluminium Silicon alloy LM6 can be improved with the addition of grain refiners and modifiers as these provide technical and economic advantages. This paper is an effort to study the effects of addition of grain refiners and modifiers to the eutectic Al – Si alloy LM6. Commercially available Al - Si alloy LM6 (eutectic = 12% Si) is grain refined with Al-5Ti-1B and Al-3B; and modified with Al-10Sr master alloys. These were added individually and then tested for its unique mechanical properties such as ultimate tensile strength, hardness and wear; which are co-related with the machining tests such as turning, surface roughness and drilling. The test results are compared with microstructure of the samples observed through SEM.The mechanical properties of this alloy can be altered after addition of master alloys, which in turn alter the grain size. Thus the results conclude that the mechanical properties of Al-Si alloys in general are controlled by a number of principal microstructural features. A fine grain size is desirable, leading to improvement of mechanical properties.

Development of Al–Nb–B master alloy with high Nb/B ratio for grain refinement of hypoeutectic Al–Si cast alloys

Al–Nb–B master alloy has been regarded as a promising grain refiner that can reduce grain size of hypoeutectic Al–Si casting alloys. However, its grain refinement performance remains to be improved. In this work, the grain refinement efficacy of Al–Nb–B master alloy is significantly enhanced by modifying the Nb/B ratio through thermodynamic calculation. An Al–Nb–B master alloy with optimum Nb/B ratio of ~ 10:1 provides a fully equiaxed structure across the sections of the Al–10Si and commercial Al–9Si–0.08Ti alloys with an average grain size below 220 μm. The phenomenon is attributed to the existence of NbAl3 and the higher number density of NbB2 at the Nb/B ratio of ~ 10:1, which offers sufficient active nucleating sites to promote the formation of smaller grains. Moreover, the segregation behavior of Si atoms and interfacial energies after doping Si are investigated by first-principles calculations, and the results reveal that Si tends to segregate to the NbAl3/α-Al interface, whereas grain refining potency of NbAl3 for Al remains unchanged. This study has implications for strategic design of Al–Si cast alloy with fine and equiaxed grain structure inoculated by grain refiner.

Experimental investigation of the size effect in high cycle fatigue: Role of the defect population in cast aluminium alloys

Cast Al-Si alloys have been widely used in automotive applications with regard to their low density and excellent thermal conductivity. Many components made of these alloys are subjected to cyclic loads which can lead to fatigue failure. Furthermore, for these materials the well know size effect in fatigue, whereby the fatigue strength is reduced when the size is increased, can be significant and need to be properly evaluated. This paper analyses the role of casting defects on the fatigue strength’s size effect sensitivity. A uniaxial fatigue testing campaign (R = 0.1) has been conducted using two cast aluminium alloys, fabricated by different casting processes (gravity die casting and lost foam casting), associated with the T7 heat treatment, and with different degrees of porosity. The fatigue response of different specimens (smooth and notched) with different stressed volumes has been investigated. The first part of this article is dedicated to the experimental characterization of the size effect in both alloys via the concept of the Highly Stressed Volume. The second part investigates the effect of the Highly Stressed Volume on the critical defect size via Kitagawa-Takahashi diagrams. The results show that the magnitude of the size effect and the experimental scatter are strongly linked to the characteristics of the defect population present in the alloy. It is revealed that the alloy B, with a high density of pore and a population of defects with relatively large size, shows non-significant size effect and less scatter in fatigue strength. In comparison, alloy A that exhibits a low density of pore and a population of defects of relatively small size manifests significant size effect and high scatter in fatigue strength.

Microstructure Study of the Stainless Steel Layer on AlSi Cast Alloy Prepared by Laser Deposition

The main aim of this study is structural changes on the layer of Al-Si cast alloy by laser austenitic stainless steel 17 246 deposition. In order to remelt the Al-Si alloy surface the laser of 1, 9 kW has been used for facing area, and 1.6 kW for the edge. The linear laser scan rate of the beam was set 450 mm.min-1 for facing area, and for the edge 550 mm.min-1. We observed that the thin surface made of austenitic stainless steel had a lot of splits. The purpose of this study is also to enhance inherent properties of the surface materials to create new product or improve on existing one.

Estimation of Solid Solution Si Concentration in Al–Si Alloy Castings Based on Dimensional Change during Heat Treatment

Estimation of Solid Solution Si Concentration in Al–Si Alloy Castings Based on Dimensional Change during Heat Treatment

Influence of Ni in high Fe containing recyclable Al-Si cast alloys

Research in recycling Al-alloy is necessary for a sustainable industrial development. Iron present in the recycled Al-alloys deteriorates its mechanical properties. The challenge, therefore, is to tackle the iron impurity using different methodologies. The present study focuses on a strategy by which iron containing beta phase could be destabilized with the addition of Ni. A large number of microstructural image, lattice parameter data and mechanical properties have been obtained using optical microscopy with state-of-the-art image analysis, FESEM with EDS and EBSD, XRD, Vickers microhardness and universal tensile testing. Based on these results, the present work provide necessary insight about the effect of Ni addition in the recycled Al-Si cast alloys containing as high as 2wt% Fe. Finally, it was concluded that up to 4wt% Ni addition could be beneficial for Al-Si alloys Si content limited to 9wt%.

Tailoring the microstructure of recycled 319 aluminum alloy aiming at high ductility

Iron has low solubility in solid aluminum and for this reason it can lead to the formation of Fe-rich intermetallic phases (such as β-AlFeSi in Al-Si cast alloys) severely impairing the ductility of the material. Spray forming is an advanced casting process that has been described as a potential technique to highly decrease the β-AlFeSi formation, consequently increasing the ductility. This paper aims to study the effect of pouring and tundish temperature in the microstructure of 319 aluminum alloy with high iron content processed by spray forming. Spray formed ingots and overspray particles were analyzed for two different processing conditions. In order to evaluate the mechanical properties, the spray formed deposits were mechanically conformed by hot swaging. Results showed that the decrease in the β-AlFeSi content strongly depends on the processing conditions. Spray formed deposits processed by hot swaging presented high ductility, allowing a wide range of possibilities to apply casting alloys with high impurity content to more valuable applications beyond the casting industry, therefore decreasing the needs for using primary alloys and contributing to the environment.

Advantages of Colour Etching in Quality Control of Recycled Al-Si Cast Alloys

Abstract Colour Metallography is a set of light metallographic microscopy methodologies that utilize phase colour contrast as a source of new structure information compared to conventional techniques. In many cases, colour contrast can be induced where no identifiable phase contrast is obtained by conventional techniques. With the help of colour contrast, we gain new information on the structure of Al-Si alloys, especially intermetallic phases, in which the benefits of its use in casting quality control are of benefit. Blue-yellow contrast is definitely more pronounced than dark grey or light grey contrast. There is no substantial reproducible colour reproduction, since it is irrelevant whether the two phases are distinguished by blue-yellow or green-ocher contrast. When using the colour contrast, the structural components differ not only according to their microscopic appearance, but also based on the knowledge of the chemical composition of alloys, interactions between structural components, knowledge of the possible influence of Al-alloys structure (e.g. refining, modifications, heat treatment). Colour contrast in quality control of Al-Si alloys was applied to AlSiMg cast alloy (AlSi7Mg0.3; AlSi7MgTi; AlSi10MgMn; etc.)

Corrosion Behaviour of Al-Si Cast Alloy Reinforced with Titanium diboride (TiB2) and Scandium (Sc)

The aluminium-silicon (Al-Si) based on Metal Matrix Composites (MMCs) is widely used in lightweight constructions and transport applications requiring a combination of high strength and ductility. A grain refinement plays a crucial role in improving characteristics and properties of Al alloys. In this investigation, titanium diboride (TiB2) and scandium (Sc) inoculants were added to the Al-Si alloys for grain refinement of an alloy. In this investigation, the corrosion resistance rate of Al-Si cast alloy reinforced by TiB2 and Sc were measured by potentiostat (AUTOLAB) instrument. The aim of this research is to investigate the corrosion rate for Al-Si-TiB2-Sc composites that immersed in different concentration of acidic solutions. Besides, the immersion time of acidic solutions also was investigated. All the samples were prepared accordingly for ASTM standard by the composition of 6.0 wt% TiB2 and 0.6wt% Sc. All the samples undergo cold mounting technique for easy handling on corrosion tests. Then the samples were immersed in two different concentrations acidic medium solutions, which were 0.1.and 1.0 M hydrochloric acids (HCl). The corrosion rate also was investigated for immersion samples of 1.0 M HCl for 21 days. From the results obtained, added TiB2 and Sc onto Al-Si alloy gave the better properties in corrosion resistance. Corrosion rates to reduce when the samples were immersed in a lower concentration of acidic medium, 0.1 HCl. However, there are some significant on the result but it still following the corrosion rates trend. Thus, improvements to reinforcement content need to be done in further research to cover the lack of this corrosion rates trend.

Strontium-modification in the stepwise solidification of A319 Al alloy: An in-situ neutron diffraction study

The modification of cast Al-Si alloys with trace Sr is common practice for the improvement of material properties. In addition to the typical morphological transformation of the eutectic Si particles, research has shown that Sr can significantly influence the evolution of multiple other phases that are observed in complex industrial Al alloys. In this study, the solidification sequence and characteristics of unmodified and Sr-modified A319 Al alloy was investigated using in-situ neutron diffraction to obtain a novel perspective of the mechanism of its phase transformations. Neutron diffraction intensity data was collected during stepwise alloy solidification from 630 to 200 °C. This enabled the production of fraction solid curves, isolated for the individual Al, Si, Al15(Fe,Mn)3Si2, Al5Mg8Cu2Si6, and Al2Cu phases in the alloy, which corresponded well with the curves simulated using FactSage™ software. The solidification analysis was complimented with optical and scanning electron microscopy, which revealed the production of a unique and fascinating microstructure in the Sr-modified alloy. As a result of the combined action of Sr-induced undercooling and long holding times during stepwise cooling, the Al15(Fe,Mn)3Si2 phase was completely and significantly transformed into numerous, fine, uniformly-dispersed polyhedrons. The unmodified, acicular growth of the Si particles was then enabled, by using the polyhedral phase as substrates for nucleation. Hence, no undercooling of the Al-Si eutectic reaction was observed for the Sr-modified alloy.

Thermal diffusivity of Al-Si cast alloys for internal combustion engines

International regulations on the reduction of fuel consumption and CO2 emissions to the atmosphere have made the transportation industry in general, and the automotive in particular, to look for the improvement of aluminium alloys used in manufacture of internal combustion engines. Smaller and lighter engines able to develop higher power outputs rely on increasing the temperature within the combustion chamber, which imply augmenting thermal and mechanical demands of the alloy used in the manufacture of powertrain components. Al-Si alloys are used due to their combination of low density, high strength and the feasibility of attaining complex shapes. Such strict demands require the design of newer engines able to dissipate the heat generated within the combustion chamber to avoid the damage that higher temperatures may cause to the alloy. The work conducted on cast aluminium-silicon alloys to evaluate their thermal diffusivity dependence with respect to temperature, chemical composition, microstructure and heat treatment imparted are presented in this work. The results show how thermal diffusivity can be enhanced by adequate design and proper heat treating practices imposed to the alloy.

Enhanced strength and ductility of A356 alloy due to composite effect of near-rapid solidification and thermo-mechanical treatment

The coarse dendritic microstructure with non-uniform distribution of eutectic Si particles leads to poor ductility of A356 alloy, thus challenging the enhancement of mechanical properties through deformation at room temperature. Here, a new processing protocol was proposed by combining near-rapid solidification with two-step thermo-mechanical treatment (TMT). To significantly improve the ductility of the alloy, near-rapid solidification, in combination with first-step TMT including equal channel angular pressing (ECAP) and intermediate heat treatment, was applied to refine eutectic Si particles and make them evenly distributed in the matrix. On this basis, a high ultimate tensile strength ∼483 MPa, with relatively good elongation to failure ∼8.1% can be achieved by the subsequent ageing treatment and composite deformation (ECAP + cryorolling) of second-step TMT. The excellent combination of strength and ductility was mainly attributed to the synergistic effect of high density of dislocations, refined nanoscale Si particles and uniform distributed eutectic Si particles arising from this fabrication processing. This work provides a new idea for the preparation of high strength Al-Si cast aluminum alloy, so that the application of Al-Si cast alloy is promisingly expected to expand.

A facile method to fabricate a novel 3D porous silicon/gold architecture for surface enhanced Raman scattering

Si-based surface enhanced Raman scattering (SERS) sensing technology is a powerful tool for the detection of various chemical and biological species. Further improvement of the simplicity, stability, sensitivity, and low cost of Si-based SERS platforms is still in great demand for real applications. In this study, the facile fabrication of three-dimensional (3D) porous Si/Au SERS platform with attractive SERS performances was reported. The developed method relied on laser-induced dendrite-like microstructure on the surface of Al-Si cast alloy followed by dealloying Al from the laser treated surface, leaving a 3D dendrite-like porous Si substrate. By sputtering, the substrate was coated with Au film to form 3D porous Si/Au SERS platform. Such 3D porous Si/Au SERS platform had high SERS sensitivity that enabled ultralow concentration detection of R6G molecules down to 10−15 M with enhancement factor in the range of 1011 to 1012. The relative standard deviation of 6.2% was obtained from 15 random SERS spectrum, indicating superior reproducibility of the as-fabricated 3D porous Si/Au SERS platform.

Understanding the Thermodynamics and Crystal Structure of Complex Fe Containing Intermetallic Phases Formed on Solidification of Aluminium Alloys

Ab initio density-functional theory calculations were carried out to investigate the energetics and structure of key Fe-containing intermetallic phases that precipitate from cast Al-Si alloys. These results were compared with published experimental information and used to provide insight into developing improved models to describe the thermodynamic properties of these phases.

Estimation of Chemical Composition of Al-Si Cast Alloys Using Image Recognition

In this study, we analyzed the chemical composition of Al-Si cast alloys from microstructural images, using image recognition and machine learning. Binary Al-Si alloys of Si = 1~10 wt% were cast and prepared as reference images in the dataset used for machine learning. The machine learning procedure was constructed with Inception V3 model. Repeated training to relate the microstructural images to their chemical composition was carried out, for up to 10,000 steps, to increase the reliability of the analysis. The peaks of similarity existed in the dataset with chemical compositions corresponding to the known target composition. The heights of the peaks became higher and the distribution of similarity became sharper with further training steps. This means that the weighted average of the chemical composition approached the target composition with increasing training steps. The correctness of the analysis increased with training steps up to 10,000, then was saturated. It was found that the chemical composition outside the dataset range could not be analyzed correctly. Analysis of the compositions between the datasets showed incorrect but reasonable results. The reliability of the chemical composition analysis using machine learning and image recognition developed in this study will increase when a vast range of reference images are collected and verified. Key words: artificial intelligence, image recognition, chemical composition, microstructure, aluminum alloy

Estimation of Mold Filling Ability and Volume Deficit Characteristics of Cast Al-Si Alloys

Estimation of Mold Filling Ability and Volume Deficit Characteristics of Cast Al-Si Alloys

Effect of Friction Stir Processing on the Microstructure, Damping Capacity, and Mechanical Properties of Al-Si Alloy

Friction stir processing (FSP) was conducted on an Al-Si casting alloy. The Si phase and Al grains of an Al-Si casting alloy were refined through FSP. Furthermore, FSP with high rotation rate led to the precipitation of Mg and Si atoms and the formation of Mg2Si phase in the Al-Si alloy. Precipitation improved the low-strain damping capacity but deteriorates high-strain damping capacity of the FSP sample at room temperature. At low rotation rate, the FSP sample exhibited excellent high-temperature damping capacity mainly because of its fine grain structure and the low density of its pinning points. The plastic instability of the Al-Si alloy was eliminated by FSP because of the refinement of the Si phase. The increase in the strength of each FSP sample was attributed to the increase in second-phase and boundary strengthening effects. Thus, the mechanical properties and damping capacity of Al-Si were enhanced after FSP.

Microstructural influences on the fatigue crack initiation and propagation mechanisms in hypo-eutectic Al-Si cast alloys

Al-Si cast alloys are accompanied by different defects and microstructural heterogeneities like porosity, varying secondary dendrite arm spacings (SDAS) and multiple appearances of the eutectic. These issues are well known but technically difficult to prevent for the industry. To improve the light weight performance of cast aluminum alloys the present work deals with influences on crack initiation and propagation mechanisms of such heterogeneities in the high-cycle-fatigue (HCF) and very-high-cycle-fatigue (VHCF) regime for the two hypo-eutectic cast aluminum alloys AlSi8Cu3 (in-series sand castings) and AlSi7Mg0.3 (laboratory gravity die castings). Furthermore, the occurrence of facet-regions and their role in early and late state of fatigue damage evolution is discussed by showing results from modified Kitagawa-Takahashi analysis and ex-situ computed tomography investigation during intermitted HCF experiments. In the early HCF regime crack initiation starts at multiple pores. Due to coalescence of these defects, shear-stress-controlled crack propagation along slip bands leads to the occurrence of facets. In the VHCF regime, porosity provides strong scattering of the number of cycles to failure. A reduction in SDAS increases the fatigue strength significantly. However, in absence of porosity fatigue crack initiation and propagation is controlled by shear stresses on facet-like slip-planes. Additionally, the barrier role against dislocation movement of eutectic regions can be shown by means of these specimens.