Al-Si Cast Alloys Research Articles

An Al-12Si/ZnS powder inoculant for eutectic silicon in Al-12Si alloy

To obtain high-performance Al-Si-based cast alloys, refinement and modification of Si phases are required. An Al-12Si/ZnS powder inoculant was designed and fabricated using a chemical bath deposition method. The efficiency of the inoculant for modifying the eutectic Si phase in as-cast Al-12Si alloy was studied. Results show that Al-12Si/ZnS powder can significantly refine the eutectic Si in Al-Si cast alloys. The best refinement effect for eutectic Si is achieved with 17.5wt.% Al-12Si/ZnS powder. Coarse long needle-shaped eutectic Si with a length of 18 µm was modified into approximately spherical shape with a diameter of 6.53 µm, which is evenly distributed throughout the alloy. The E2EM model calculation indicates that the inter-plane misfit (Fp) and inter-atomic spacing misfit (Fr) between ZnS and Si are all less than 0.5%, which confirms that ZnS is a potential nucleation site for Si phase. The hardness, tensile strength, and elongation of Al-12Si alloys modified with 17.5% Al-12Si/ZnS powder increase 6.30%, 16.18% and 55.45%, respectively, compared to the unmodified Al-12Si alloy. The fracture behavior of the alloy with 17.5wt.% Al-12Si/ZnS powder is dominated by transgranular fracture supplemented by intergranular fracture.

Effect of Intermetallics and Drill Materials on the Machinability of Al-Si Cast Alloys.

The present study was conducted on the machinability of 396 alloy (containing approximately 11% Si) and B319.2 alloy mainly to emphasize the effects of Fe-intermetallics, i.e., α-Fe, β-Fe, and sludge. The results demonstrate that the presence of sludge in the form of hard spots has a significant effect on cutting forces and tool life, in that it decreases drill life by 50% compared to the base alloy. The formation of the α-Fe phase in the M1 base alloy has a beneficial effect on tool life in that this alloy produces the highest number of holes drilled compared to alloys containing sludge or β-Fe; this result may be explained by the fact that the formation of the α-Fe intermetallic, with its rounded Chinese script morphology and its presence within α-Al dendrites, is expected to improve matrix homogeneity via hardening of the soft α-Al dendrites. Increasing the Fe-content from 0.5% to 1% in the 396-T6 alloy containing 0.5% Mn produces a distinct improvement in alloy machinability in terms of cutting force and tool life. The addition of Fe and/or Mn appears to have no discernible effect on the build-up edge area (BUE) and chip shape.

Effect of heat treatment and electric discharge alloying on the lubricated tribology of Al–Si alloy fabricated by selective laser melting

Selective Laser Melting (SLM) is an innovative additive manufacturing technology that facilitates the design and manufacture of complex lightweight parts with improved mechanical properties. The current study investigates the impact of post-processing such as heat treatment and Electric Discharge Alloying (EDA) on the lubricated tribological behaviour of SLM Al–Si alloy at ambient and elevated temperatures in comparison with the tribological behaviour of conventionally cast Al–Si alloy. The lubricated sliding wear experiment conducted using a Pin on Disk (POD) tribometer with EN-31 alloyed steel as a counter body. The EDA treatment is highly appealing and enhanced the wear resistance of SLM Al–Si alloy by 14.07% and 24.07% at ambient and elevated temperatures, respectively. Moreover, the EDA treatment increased the wear resistance of cast Al–Si alloy by 28.82% and 46.28% at ambient and high temperatures, respectively, due to the development of a wear-resistant carbide (SiC) and oxide (Al2O3) rich modified layer on the surface. The T6 heat treatment in SLM Al–Si alloy caused deterioration in wear resistance by 10.74% and 36.73% at ambient and elevated temperature, respectively, due to the coarsening of the finer microstructure formed during SLM. In contrast, the T6 heat treatment in cast Al–Si alloy is highly effective in terms of wear resistance with an improvement of 13.26% and 13.64% at ambient and elevated temperature, respectively, due to the hardening effect caused by heat treatment. The prominent wear mechanism identified for all samples at both experimental conditions is severe abrasive wear due to plastic deformation.

Effects of melt thermal treatment on cast Al-Si alloys: A review

The shape and size of primary phases (α-Al and primary Si in hypoeutectic and hypereutectic alloys, respectively), and that of eutectic Si phase significantly affect the mechanical properties of cast Al-Si alloys. The Al-Si alloys prepared by the conventional casting method have large-sized primary phases and needle-shaped eutectic Si phases along with their uneven distribution in the microstructure. This leads to poor mechanical properties in those alloys. This paper presents a review on a modified casting process known as melt thermal treatment, which has the potential to positively change the shape and size of primary and eutectic phases in Al-Si alloy without any foreign additives. Various researches that have been carried out to study the effect of melt thermal treatment on microstructure and different properties of Al-Si alloys are discussed here.

Uniform Fatigue Damage Tolerance Assessment for Additively Manufactured and Cast Al-Si Alloys by Linking Novel Elastic-Plastic Facture Mechanical Approaches

Uniform Fatigue Damage Tolerance Assessment for Additively Manufactured and Cast Al-Si Alloys by Linking Novel Elastic-Plastic Facture Mechanical Approaches

Scatter and size effect in High Cycle Fatigue of cast aluminum-silicon alloys: A comprehensive experimental investigation

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. For these materials, the well-known size effect in fatigue, whereby the fatigue strength is reduced when the size is increased, can be significant and needs to be properly evaluated. This paper analyses the role of casting defects on the fatigue scatter and size effect. A uniaxial fatigue testing campaign (R=0.1) has been conducted using two cast aluminum 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 about the experimental characterization of the size effect and scatter 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 and the establishment of Kitagawa-Takahashi diagram. It is shown that the alloy B, with a population of defects of large size, shows a slight size effect and low scatter. In comparison, alloy A that exhibits a population of defects of relatively small size manifests significant size effect and high scatter.

Qualification of uniform fatigue damage tolerance law for additively manufactured and cast Al-Si alloys

The demand on lightweight structures and materials are steadily growing in automotive and aerospace industries. Hypo-eutectic Al-Si alloys are promising candidates due to its high specific material strength and corrosion resistance. Near net shape manufacturing by additive manufacturing (AM) or castings allow a high resource efficiency. The complex geometries lead to a wide range of structural features due to process-induced variations in local cooling rate. Therefore, the relationships between structural characteristics (e.g. dendrites, grain, eutectic, porosity, lack of fusion) and fatigue behavior have to be understood to enable a lightweight and reliable design of Al-Si alloys. In this study, the effect of process and process-induced structural characteristics on stress-strain behavior (quasi-static, cyclic) and high cycle fatigue behavior were characterized. The specimens were processed by laser-based powder bed fusion (PBF-LB) and sand casting (SC) with variation in porosity and dendrite arm spacing. Hereby, the age-hardenable Al-Si alloys AlSi10Mg (AM, SC) and AlSi7Mg (SC) were investigated. AM batches were tested in as-built condition. All casting batches got a HIP densification and T6 heat treatment. The fatigue results were analyzed based on nominal stresses according to Woehler (S-N curve) and local stress intensity based on linear-elastic fracture mechanics (stress intensity factor) as well as elastic-plastic fracture mechanics (J integral). J integral based Shiozawa diagrams allowed a sufficient and uniform fatigue damage tolerance (FDT) assessment for all AM and SC alloys. Hereby, the FDT of Al-Si alloys were dominated by defects (size, position) and cyclic stress-strain behavior (yield strength, cyclic hardening).

Influence of modifying elements on the structure and mechanical properties of casting Al-Si alloys

The state of scientific research on the modification of aluminum-silicon (Al-Si) alloy with strontium, sodium, phosphorus, which are widely employed in industrial alloys, and the modification of Al-Si alloy with intensively studied rare-earth elements (cerium, europium, samarium and others) was analyzed. Scientific articles related to the study of the effect of modifiers on the mechanical properties, mainly on the strength and ductility of hypoeutectic, eutectic and hypereutectic alloys was considered. On the basis of a literary data analysis, ways of improving the mechanical properties have been proposed by jointly modifying several elements, the possibility of forming the solely eutectic structure in the hypereutectic composition alloy 0.01 wt% strontium (Sr) modified and directionally crystallized at a rate that provides paired growth of the eutectic components is noted. This composition of Al-Si alloy has superfine-grained eutectic structure, its strength and ductility exceed the mechanical properties of Al-Si alloys obtained by other techniques. Keywords: rare-earth elements, eutectic, microstructure, elongation, tensile strength.

Atomistic modeling of interface strengthening in Al-Si eutectic alloys

Al-Si cast alloys are usually composed of α-Al and Al-Si eutectic. Si flakes and Al matrix generally hold cube-on-cube orientation relationship with the primary interface (111)Al∥(111)Si. Extensive experimental studies demonstrated that Si flakes cannot significantly improve mechanical properties of Al-Si cast alloys. We hypothesize that the weak strengthening effect associated with Si flakes might be attributed to thermomechanical properties of Al-Si interfaces besides their morphologies. To characterize Al-Si interfaces with a large lattice mismatch (> 30%), we proposed the quasi-coincident site lattice (Q-CSL) as reference lattice, and demonstrated that the Q-CSL Al-Si coherent interface has three characteristic coherent structures, one stable and low energy structure and two metastable and high energy structures. The translation vectors for the same type of coherent Q-CSL structures are consistent with three displacement shift complete (DSC) vectors. The two metastable structures can be obtained by shifting the low energy structure with three partial DSC vectors. Semi-coherent interface is composed of the low energy Q-CSL patches and three sets of interface misfit dislocations with Burgers vectors same as the DSC vectors. Atomistic simulations revealed that Al-Si interface exhibits low shear resistance. Ideal shear strength of the Q-CSL coherent interface is 110 MPa and semi-coherent interface is 20 MPa. The low shear resistance is attributed to the glide of interface misfit dislocations. Al-Si interface also exhibits low formation and migration energies of point defects. Owing to low shear strength and low formation and migration energies of point defects, interface sliding or shear readily happen under mechanical loading or during dislocation-interface interactions. Lattice dislocations can cross slip onto or climb along Al-Si interfaces. These reactions decrease the number of accumulated dislocation loops around Si flakes and promote nucleation and emission of lattice dislocations from Al-Si interfaces to matrix, consequently reduce the repulsive force on approaching dislocations and weaken Si flakes strengthening effect. In situ tension and compression tests in a scanning electron microscope reveal relatively weak strengthening effect due to Si flakes, consistent with the computed dislocation interaction with interfaces and shear behavior of interfaces.

Fabrication and post processing techniques to enhance the strength of Al-Si alloy

The alloy of aluminium and silicon was fabricated at the shop floor level and post processed with the sole intention of enhancing the tensile and compression strengths of the alloy for engine piston application. To that extent, alloys of aluminium with varying fractions of silicon in the range of 12%, 18% and 24% by weight was fabricated using the die casting technique. The alloys casted in the form of cylindrical rods were post processed using heat treatment techniques. This post processing techniques includes the heat treatments at 500 °C for one set of casted Al-Si alloys and 520 °C for the other set of casted Al-Si alloys, each for a period of 3 h and then water quenched. Following which, both the sets of alloys were age hardened, by heat treating at 155 °C for a period 2 h and then air cooled. The tensile and compression tests were conducted to evaluate the ultimate tensile and compression stresses of the heat treated specimens and the results obtained were compared with the stresses obtained for the as cast Al-Si alloys. It was observed that the Al-Si alloy fabricated with 18% silicon, heat treated at 500 °C for a period of 3 h and age hardened at 155 °C had shown an excellent tensile strength improvement at 89.91 MPa. In addition, Al-Si alloy fabricated with 18% silicon, but heat treated at 520 °C for a period of 3 h and age hardened at 155 °C had shown an excellent compression strength improvement at 381.97 MPa. Thus, it can be comprehended that the fabrication of Al-Si alloy with 18% silicon and the post processing techniques adopted through heat treatments showed a vast improvement in tensile and compression strengths, which can be applicable for engine pistons.

Correction to: Metallurgical Parameters Controlling Fragmentation and Spheroidization Processes of Eutectic Si Particles in Al–Si Cast Alloys

Correction to: Metallurgical Parameters Controlling Fragmentation and Spheroidization Processes of Eutectic Si Particles in Al–Si Cast Alloys

Metallurgical Parameters Controlling Fragmentation and Spheroidization Processes of Eutectic Si Particles in Al-Si Cast Alloys

Metallurgical Parameters Controlling Fragmentation and Spheroidization Processes of Eutectic Si Particles in Al-Si Cast Alloys

Generating the Microstructure of Al-Si Cast Alloys Using Machine Learning

In this study, we constructed a deep convolutional generative adversarial network (DCGAN) to generate the microstructural images that imitate the real microstructures of binary Al-Si cast alloys. We prepared four combinations of alloys, Al-6wt%Si, Al-9wt%Si, Al-12wt%Si and Al-15wt%Si for machine learning. DCGAN is composed of a generator and a discriminator. The discriminator has a typical convolutional neural network (CNN), and the generator has an inverse shaped CNN. The fake images generated using DCGAN were similar to real microstructural images. However, they showed some strange morphology, including dendrites without directionality, and deformed Si crystals. Verification with Inception V3 revealed that the fake images generated using DCGAN were well classified into the target categories. Even the visually imperfect images in the initial training iterations showed high similarity to the target. It seems that the imperfect images had enough microstructural characteristics to satisfy the classification, even though human cannot recognize the images. Cross validation was carried out using real, fake and other test images. When the training dataset had the fake images only, the real and test images showed high similarities to the target categories. When the training dataset contained both the real and fake images, the similarity at the target categories were high enough to meet the right answers. We concluded that the DCGAN developed for microstructural images in this study is highly useful for data augmentation for rare microstructures.

Improvement of oxide layers formed by plasma electrolytic oxidation on cast Al Si alloy by incorporating TiC nanoparticles

The effect of titanium carbide nanoparticles (TiC NPs) on the structure, chemical and phase composition of the oxide layers obtained by plasma electrolytic oxidation (PEO) on the aluminum-silicon alloy (7.5 wt% Si) was investigated. A significant increase in hardness and effective elastic modulus (~1.4 times), wear resistance (~3 times) and corrosion resistance (~10 times) along with a substantial increase of the layer thickness (about 30%) were found to be connected with chemically inert incorporation of TiC NPs into the oxide layer, while the volume fraction of the incorporated particles in the oxide layer was only about 1%. Improvement of the layer properties was concerned with a decrease in the number of pores and cracks, an increase in the layer crystallinity, and a shift in the phase composition towards more stable phases such as mullite. The assumed mechanism of the TiC NPs effect is a decrease in the breakdown voltage of vapor-gas bubbles (VGB) due to sparking (local breakdowns) from cathodic electrolyte onto the TiC nanoparticles incorporated into the microchannel walls. Sparking to these particles can promote ionization of the gaseous medium, providing earlier microarc discharge through the entire VGB. It results in a substantial increase in the number of microarc discharges, which then initiate larger volumes of melted splash metal and subsequently larger volumes of oxide layer. The higher average temperature results in a decrease in the defectiveness of the macrostructure, the removal of gas from the layer, the growth of crystallites, the removal of residual strains, and a stabilization in the phase composition.

Comparative Study on Microstructure and Corrosion Resistance of Al-Si Alloy Cast from Sand Mold and Binder Jetting Mold

This investigation is focused on the corrosion evaluation of an as-cast Al-Si alloy, obtained by two different casting methods: traditional sand casting and three-printing casting, using a binder jetted mold. The experimental results are discussed in terms of chemical composition, microstructure, hardness, and corrosion behavior of two different casting parts. The microstructure and composition of the sample before and after the corrosion tests was analyzed using light microscopy (OM), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX) and X-ray diffraction (DRX). The corrosion of the two processed castings was analyzed using anodic polarization (PA) test and electrochemical impedance spectroscopy (EIS) in an aerated solution of 3.5% by weight NaCl, similar to the seawater environment. After the corrosion process, the samples were analyzed by inductively coupled plasma/optical emission spectrometry (ICP/OES); the composition was used to determine the chloride solution after immersion times. The sample processed by binder jetting mold showed higher corrosion resistance with nobler potentials, lower corrosion densities, higher polarization resistance, and more stable passive layers than the sample processed by sand casting. This improvement of corrosion resistance could be related to the presence of coarse silicon particles, which decrease of cathodic/anodic ratio and the number of micro-galvanic couples, and the lower amount of intermetallic β Al-Fe-Si phase observed in cast alloy solidified in binder jetting mold.

Fast aging strengthening by hybrid precipitates in high pressure die-cast Al-Si-Cu-Mg-Zn alloy

The improvement on mechanical properties in high pressure die casting (HPDC) Al Si alloys is an important issue for their application. In this present study, it is found that the artificial aging with low-temperature and short-time can remarkably improve the mechanical properties of HPDC Al-Si-Cu-Mg-Zn alloy, which can avoid heat-treatable defect formation of HPDC Al alloy and be applied in industrial production. The experimental results indicate that the as-cast microstructure of HPDC Al-Si-Cu-Mg-Mn-Zn alloy shows uniformly-distributed GB phases, fine grains and fine AlFeMnSi granular phases. Ascribed to the high cooling rate of HPDC, significant refinement of the obtained microstructure can be achieved. In addition, with the increase of aging temperature from 160 to 220 °C, the θ′ nanoscale phase can be sufficiently precipitated which results in the formation of hybrid precipitates, thus providing a better strengthening effect. The short-time artificial aging at 220 °C for 30 min remarkably improves the hardness of alloy from 115 to 145 HV with an increment of 26.1%. It is found that the hybrid precipitates including β″, Q′ and θ′ are believed to be responsible for such high strengthening contribution by superimposed strengthening in Al-matrix. The Cu-containing nano-precipitates are considered to promote the strengthening of short-time artificial aging in the HPDC Al-Si-Cu-Mg-Zn alloy. The present study provides a feasible and high-efficiency method to prepared HPDC alloy with excellent mechanical properties. • Aging-hardening behavior of HPDC Al-Si-Cu-Mg-Zn alloy was investigated. • Precipitation sequence of aging HPDC Al-Si-Cu-Mg-Zn alloy was elucidated. • Significant improvement on hardness (26.1%) was achieved due to hybrid precipitates. • Precipitation hardening effect on aging HPDC Al-Si-Cu-Mg-Zn alloy was revealed.

Simulation and experimental investigation of multi-walled carbon nanotubes/aluminum composite fabrication using friction stir processing

Multi-walled carbon nanotube/aluminum composites are fabricated on Al–Si cast alloy employing friction stir processing. First, the microstructure of the stir zone, as well as the effect of process parameters on the size of silicon particles, is investigated. Then, the process is numerically simulated using a thermo-mechanically coupled three-dimensional finite element method model. Material flow, as the primary reason for the dispersion of reinforcing particles, is considered in the numerical model, and proper conditions to obtain a uniform dispersion of multi-walled carbon nanotubes are determined. Scanning electron microscope analysis is carried out to consider the particle distribution in the texture of the stir zone. The results show that the particle distribution improves significantly by changing the tool rotation direction between the friction stir processing passes. The hardness test is accomplished on the cross-section of the friction stir processed specimens, and finally, the wear test is performed to compare the wear resistance of the composites with the base alloy. The results show that the wear resistance and hardness of the produced composites are considerably enhanced compared to the base alloy.

High performance tribological coatings on a secondary cast Al–Si alloy generated by Plasma Electrolytic Oxidation

Due to their outstanding properties, including low density or high-strength-to-weight ratio, cast Al–Si alloys are attractive materials. Nevertheless, their low wear and corrosion resistance still remain a critical issue for several applications. The present work is focused on the obtention of PEO coatings on a secondary cast Al–Si alloy (EN AC-46500) and the in-depth study of the properties derived from the use of two developed aluminate-based electrolytes.All the obtained PEO coatings have been characterized in terms of their thickness and roughness, morphology, and composition. Reciprocal wear tests have been performed in order to evaluate the tribological behavior of the PEO layers, while their anti-corrosion properties have been analyzed throughout Potentiodynamic Polarization and Electrochemical Impedance Spectroscopy.Our findings suggest that the aluminate-based electrolytes led to an increase in coating thickness of density, while providing a notable improvement on the surface hardness in comparison with the uncoated Al–Si alloy. All the PEO coatings tested exhibited excellent wear resistance and an improved anti-corrosion behavior compared with the uncoated Al–Si alloy. Furthermore, K2TiF6-containing electrolyte promoted the obtention of PEO coatings that provided the highest protection against wear and corrosion to the cast Al–Si alloy treated.

In-situ study of effects of heat treatments and loading methods on fracture behaviors of a cast Al–Si alloy

In order to study the effects of heat treatment and loading methods on the dynamical fracture behaviors of Al–Si cast alloys, in-situ scanning electron microscope tensile/compression tests were performed. The results showed that the microcracks in a cast Al–Si alloy mainly originated from eutectic silicon particles and intermetallic compound particles, and particles with larger aspect ratios had a greater tendency to crack. In the non-heat-treated alloy, the cracks preferentially propagated along the Al/Si eutectic interface, while in the heat-treated alloy, the cracks propagated mainly along the slip band. The cracks are almost parallel to the loading axis during compression, while they are mainly perpendicular to the loading axis during the tension process. At the same time, it was found that particles of 0–50° or 130–180° (the angle between the long axis of the particles and the loading axis) are more likely to break, independent of the heat treatments and loading methods.

Interaction of Fe‐Containing, Secondary Al–Si Alloy with Oxide and Carbon‐Containing Ceramics for Fe Removal

Fe is a detrimental impurity element in secondary, i.e., recycled, Al–Si cast alloys for castability and mechanical properties. Fe removal can be achieved by binding Fe into Fe‐containing, primary particles and removing these from the, thus, Fe‐depleted Al–Si alloy melt. Expanding the application of filters beyond the removal of nonmetallic inclusions to increase the Fe‐removal efficiency can contribute to production of high‐quality, secondary Al–Si alloys. The usability of Al2O3, 3Al2O3 · 2SiO2, MgAl2O4, Al2O3–C, and SiC filter materials in contact with Al7.1Si, Al7.1Si1.5Fe, and Al7.1Si0.75Fe0.75Mn alloys is evaluated in sessile‐drop and crucible experiments regarding wettability, chemical interaction, nucleation, particle formation, and the subsequent effect on the alloy composition. The Al–Si melts in contact with Al2O3 act as nonreactive, low‐wetting reference systems. MgAl2O4 and SiO2 in 3Al2O3 · 2SiO2 are reduced, forming low‐wetting Al2O3, whereas Mg and Si enrich in the droplet. In contact with SiC and Al2O3–C, a thin layer of high‐wetting Al4C3 is formed. In case of Al2O3–C, primary Fe‐containing particles are specifically attached to the Al4C3 layer, which is associated with oriented growth of that layer. The remaining Fe content in the melt is 0.9 at% and beneficial kinetic effects for the Fe removal are suggested.