Hypereutectic Al-Si Alloys Research Articles

Ultra-rapid and low-temperature soldering of hypereutectic Al-Si alloys by ultrasonic-assisted soldering with In interlayer in air for electronic application

Hypereutectic Al-Si alloys were soldered by an ultrasonic-assisted soldering with In interlayer for only 0.1 s at 160 °C in air. The introduction of ultrasonic vibration into the soldering process promoted the formation of the liquid phase by its acoustic softening effect, ultrasonic cavitation effect and acoustic streaming. The effects of ultrasonic vibration on the formation of Al-In liquid phase were also discussed. The microstructure evolution of solder joint and the migration of Si particles were influenced by ultrasonic vibration. The complex solder joint obtained by the ultrasonic-assisted approach consisted of Si particles and Al-In solid solution. Si particles could be regarded as tracers and reinforced phase. The influence of ultrasonic vibration time, pressure and temperature on the microstructure of the solder joint was investigated. The effect of ultrasonic vibration on shear strength of the joints was also discussed. Image-Pro-Plus Analysis was used to estimate content of Si particles in solder joint. The shear strength of the joints was obtained, when the suitable ultrasonic vibration time, temperature and pressure were chosen.

Creep properties and microstructure evolution at 260–300 °C of AlSi10Mg manufactured via laser powder-bed fusion

The aging behavior and creep resistance of eutectic AlSi10Mg (Al–10Si-0.6Mg, wt.%) manufactured by laser powder bed fusion (L-PBF) are studied at 260 and 300 °C. The Si phase, which forms a fine interconnected network of 100–200 nm filaments in the as-printed alloy, coarsens into blocky, 2–3 μm particles after 1 month exposure at 260 and 300 °C, with hardness decreasing following a power-law with exponent n = 0.06–0.08. AlSi10Mg with ∼1 μm Si particles (achieved by aging at 300 °C for 96 h) exhibits creep resistance at 260 and 300 °C, for test durations of a few days, comparable to those of (i) cast alloys: hypereutectic Al–Si alloys with coarse Si particles and eutectic Al–Ce, Al–Ce–Ni with much finer, and more coarsening-resistant eutectics phases (e.g., Al11Ce3, Al3Ni); and (ii) L-PBF Al–Mg–Zr alloys. At 260 and 300 °C, our L-PBF AlSi10Mg shows a power-law creep behavior with high apparent stress exponents (na = 10–13, higher than n = 4.0 for Al–Mg) for strain rates between ∼10−8 and ∼10−4 s−1. Also, a high apparent creep activation energy Qa = 256 kJ/mol is measured between 200 and 320 °C at 45 MPa, compared to Q = 142 kJ/mol for Al. These high apparent stress exponent and activation energy are consistent with power-law dislocation creep with a threshold stress, originating from load-transfer from the creeping Al(Mg) matrix to non-creeping Si particles.

Influence of Grain Refiner, Modifier and Graphene on the Dry Sliding Wear of Hypereutectic Al–Si Alloys

Influence of Grain Refiner, Modifier and Graphene on the Dry Sliding Wear of Hypereutectic Al–Si Alloys

Primary Si refinement and eutectic Si modification in Al-20Si via P-Ce addition

Enhancing the mechanical properties of hypereutectic Al-Si alloys by refining the primary and eutectic Si morphology is very challenging. In this study, the refinement mechanism of primary and eutectic Si morphologies via the simultaneous addition of P-Ce into the Al-20Si alloy was studied. Microstructural analysis revealed that the primary and eutectic Si morphologies were significantly refined, which increased the tensile strength. Furthermore, the addition of Ce, up to 0.6 wt%, can result in the formation of Ce-rich intermetallic phases, which may lead to a significantly increased tensile strength while retaining the ductility of the alloy. The ultimate tensile strength of the Al-20Si alloy increased from 96 to 175 MPa, and the elongation increased from 1.0% to 1.7% with the addition of P-Ce. Moreover, the wear resistance of the alloy improved. The added P and Ce did not react with each other to form an intermetallic compound; therefore, this method can simultaneously refine primary and eutectic Si.

Microstructural evolution in as-cast hypereutectic Al-Si alloys with different La additions

Abstract The microstructure of as-cast hypereutectic Al-(17 or 25) Si-xLa (x - 0, 0.4, 1, 3, 6 wt.%) alloys and the effect of La on the Si phase have been investigated. The microstructure was examined using optical and electron microscopy. The modification effects of La addition on the morphology and size of both the primary and the eutectic Si were observed. However, such effects are uneven and there seems no systematic change for the effectiveness of La modification with increasing La contents. The modification of La may be explained by the suppression of the growth of Si crystals through reduction of the eutectic reaction temperature or through enveloping of primary Si crystals, or additional twinning. Large particles of La-rich compounds are always observed associated with large primary Si crystals and unmodified eutectic Si crystals, while small La-rich particles are associated with small primary Si crystals and modified eutectic Si crystals. The overall concentration of La-rich compounds, formed in the Al–Si alloys containing more than 1 wt.% La, could be represented as a ternary AlSi2La2 phase, which actually contains the LaSi2 phase and an unknown ternary Al x Si y La phase.

Microstructure and Wear Characteristics of Multilayer Laser-Cladded Hypereutectic Al-Si Alloys

In this study, a multilayer laser-cladding method was used to increase the Si content in a hypereutectic Al-Si alloy laser cladding. One-, two-, and three-layer claddings were produced by printing Si powder paste on A1050 aluminum surfaces using 180-, 210-, and 250-㎛-thick plastic tape, respectively, and then irradiating laser pulses over them. The two- and three-layer claddings were produced by printing on the one- and two-layer cladding surfaces, respectively. The one-layer cladding had a thickness of approximately 190 ㎛ and was uniform and defectless. The cladding had a chemical composition of Al-20.2 wt.% Si and had a fine eutectic Al-Si microstructure in most regions. By contrast, the two-layer cladding had a thickness of approximately 250 ㎛ and exhibited many pores and some cracks. The cladding had a chemical composition of Al-60.5 wt.% Si and a hypereutectic Al-Si microstructure with many coarse primary Si particles. Finally, the three-layer cladding had a thickness of approximately 280 ㎛ and exhibited many large pores and a few large cracks. The cladding had a chemical composition of Al-72.6 wt.% Si and a hypereutectic Al-Si microstructure with very coarse primary Si particles. Block-on-roll wear tests were then performed on the claddings. The weight losses in the one-, two-, and three-layer claddings following the wear test were 5.5, 7.7, and 8.3 mg, respectively.

Morphologically templated nucleation of primary Si on AlP in hypereutectic Al-Si alloys

AlP has been widely used as an effective heterogenous nucleus for primary Si phase in hypereutectic Al-Si alloys, but the morphological correlation between AlP and primary Si is still confusing. In the present work, the morphologies of AlP crystals were studied comprehensively by experimental observation and theorical prediction. It is found that AlP collected from an Al-0.03P melt could be divided into two categories: spinel twin crystals and non-twin crystals. During the nucleation process, these two kinds of AlP crystals triggered morphologically templated nucleation of primary Si phase, resulting in the formation of hexagonal primary Si twin and octahedral non-twin crystals, respectively. As such, the percentage of primary Si twin crystals in the experimental Al-18Si alloy was also increased obviously after the morphologically templated nucleation via AlP. The morphologically templated nucleation also eliminated the dendritic growth of primary Si phase and the formation of hopper structures inside primary Si, forcing primary Si to maintain to be faceted solid crystals through layer-by-layer growing mechanism. The insight into morphologically templated nucleation offers a new view in understanding the mechanism of heterogeneous nucleation of primary Si phase on AlP nuclei.

Effects of sintering techniques and parameters on microstructure and mechanical properties of Al-15Si-2,5Cu-0.5Mg compacts and Al-15Si-2,5Cu-0.5Mg/B4C composites

In this study, Al-Si compacts and Al-Si/B4C composites were produced from hypereutectic Al-Si alloy powders by cold pressing/conventional sintering and cold pressing/microwave sintering techniques. The effects of sintering temperature, sintering time and B4C particle addition on microstructural properties, density, hardness and transverse rupture strength were investigated. The phases and intermetallic compounds formed in the microstructure were determined by X-ray diffraction. Densities of the samples were measured by Archimedes’ technique. Macro hardness measurements were carried out with Brinell hardness test. Three-point bending tests were applied to the samples according to ASTM-B528–16. Elemental Al regions, master alloy (Al-Si-Cu-Mg) regions, primary Si particles and Cu- and Mg-rich secondary phases were determined in the microstructure. It was determined that the Cu- and Mg-rich secondary phases are θ(CuAl2), β(Mg2Si), γ(Al2CuMg) phases. An increase in porosity was determined in conventional sintered samples compared to green Al-Si specimens. In addition, it was observed that the amount of porosity increases, grain size and primary Si grains coarse with increasing sintering temperature in conventional sintering. The change in the amount of pores of the samples produced by microwave sintering without holding time at the sintering temperature is not as obvious as in conventional sintering. Similar microstructures were obtained in the samples at increasing sintering temperatures in microwave sintering. In the samples produced by conventional sintering, the hardness value decreased with increasing sintering temperature. Addition of 5 wt% B4C caused an increase in hardness at all sintering temperatures. The addition of 10 and 15 wt% B4C caused a decrease in hardness. In microwave sintering, the general trend in hardness change was a decrease with increasing B4C particle addition and increasing sintering time. Transverse rupture strength values close to and similar to each other in conventional sintered samples were obtained at different sintering temperatures. Transverse rupture strength values increased with the addition of 5 wt% B4C particles, and decreased with the addition of 10 and 15 wt% B4C particles.

Metastable transition temperature in undercooled hypereutectic Al-Si alloys

The present study proposes a novel approach to predict the transition temperature at which the metastable zone changes to the labile zone during the undercooling of hypereutectic Al-Si alloys. The results show that the silicon content and the undercooling strongly affect the transition temperature and the energy barrier to start the spontaneous nucleation. The energy barrier predicted at the transition temperature was in the order of 10−19J. Mixing of two precursor alloys, Ostwald-Miers diagram, and transition temperature were employed to design conditions at which the microstructure of Al-14 and Al-17 wt%Si alloys forming with free primary silicon or small size primary silicon compared with conventional microstructure without adding a grain refiner.

The microstructural and wear properties improvement by manganese addition in Al-14Si hypereutectic alloy

Hyper eutectic Al-Si alloys, which are a great candidate for aerospace and automotive industries and are utilized to manufacture engine blocks, cylinder heads and pistons, rocker arms and fraction plates, all of which can reduce and improve vehicle emissions. The goal of this investigation is to make an Al-14Si alloy with different proportions of manganese as an addition to produce a composite using the stir casting method. The effect of manganese in microstructure and impact on the morphology of silicon, both primary and eutectic was highlighted in this paper. The amorphous form of silicon (primary) and silicon (eutectic) is changed to the fine globular shape of primary Si and fibrous and numerous fine eutectic Si. With the inclusion of Mn, the mechanical properties and wear characteristics of the composites are determined. Increase in manganese content decreases the wear rate in Al-14Si-1.5Mn.The microstructural-properties relations are co-related utilizing the addition of manganese into the Al-14Si alloy.

Сравнительный анализ изменения структуры и свойств сплавов системы Al–Si, подвергнутых электровзрывному легированию

The paper presents the comparative analysis of the structure and mechanical properties (microhardness) of the surface layers of the hypoeutectic Al–11Si alloy and hypereutectic Al–20Si alloy exposed to electroexplosive alloying (treatment mode: aluminum foil mass is 58.9 mg; Y2O3 powder mass is 88.3 mg; the discharge voltage is 2.6 kV). During the research, the authors identified that the Al–11Si alloy initial structure mainly consists of the Al solid solution grains. Eutectic grains are located along the grain boundaries and at the joints of aluminum grain boundaries. In the Al–11Si alloy, the aluminum grain size varies from 25 μm to 100 μm, and the Al–Si eutectic grain size varies within 10–30 μm. The hypereutectic composition Al–20Si alloy in the initial state is characterized by the presence of primary silicon inclusions predominantly of a plate-like shape. The sizes of these inclusions reach 120 μm. After electroexplosive alloying, in the Al–11Si alloy, the author identified the formation of a multilayer structure consisting of a highly-porous coating irregular in thickness, a liquid-phase alloying layer, and a heat-affected layer. The modified layer thickness for the Al–11Si alloy varies in the range of 33–60 μm, and for the Al–20Si alloy, the modified layer thickness varies within 20–100 μm. The microhardness value of the initial hypoeutectic Al–11Si alloy was 64 HV 0.05, for the hypereutectic Al–20Si alloy – 71 HV 0.05. It can be noted that the microhardness of the Al–11Si alloy surface layer exceeds the initial material microhardness more than 2.5 times. In the Al–20Si alloy, the surface layer microhardness exceeds the one of the initial material more than twice. With the increase of the distance from the modification surface, the microhardness decreases and reaches the initial alloy value at the depth of ≈90 μm.

Effect of addition of 3 %Al2O3 on mechanical and microstructural properties in Al-16Si hypereutectic alloys with pouring temperature

It is well know that the mechanical properties of hypereutectic Al-Si alloys are affected by the size, volume fraction and distribution of primary and eutectic Si particles. However, the pouring temperature of the alloy also acts as the vital role for simultaneous refine and modifying Si particles in hypereutectic Al-Si alloys by conventional means. The particles distribution of nano particles on the melt is different at different pouring temperature which affects the physical, mechanical and the microstructural behavior of Al-Si alloys. Various content of gamma Al2O3 nano particles were added in hypereutectic Al-16Si alloy melt and further dispersed through an ultrasonic cavitation based technique. The cast hypereutectic Al-16Si alloy with the nano particles’ addition showed a significant enhancement in hardness, strengths and ductility. The wear behaviour of the materials depends on the distribution of intermetallic compound over melt. This paper suggests that gamma Al203 nano particles effectively induced simultaneous refinement of primary Si and modification of eutectic Si, resulting in superior ductility enhancement that is much higher than those conventional methods can offer. Moreover, the large plate eutectic Si particles were also modified into fine core particles. The result could have great potential for numerous applications. The experiment has been performed on a group of specimens under different loads and with different speeds. We observe from the experiment that, with the increase in Al2O3 content wearing tendency decreases due to formation of Al-Si intermetallic compounds.

Effect of grain refiner, modifier and graphene on the mechanical properties of hyper eutectic Al-Si alloys by experimental and numerical investigation

The present work focuses on the study of mechanical properties of die cast hypereutectic Al-16Si alloys that are subjected to grain refinement and modification. It further deals with the study of the influence of the reinforcement of graphene to the sample that is simultaneously grain refined and modified. Hyper eutectic Al-16Si alloys are die casted with five different compositions. The Vickers hardness test and tensile strength test are performed on the all the casted samples. The Optical microstructure examination of the specimens is performed. The numerical simulation data derived from finite element analysis of the tensile test is validated against experimental tensile test results and both were found to coincide. Using experimental data, two alternative constitutive models, namely the modified Johnson Cook (m-JC) model and the integrated JC-ZA model, were formulated on the investigated materials for precise flow stress behaviour prediction. The JC-ZA model's integration is expected to improve prediction power in relevant consideration conditions.

Fabrication of Hypereutectic Al-Si Alloy with Improved Mechanical and Thermal Properties by Hot Extrusion

Fabrication of Hypereutectic Al-Si Alloy with Improved Mechanical and Thermal Properties by Hot Extrusion

Effect of Melt Purification Treatment on the Solidified Microstructure of Hypereutectic Al-Si Alloys

Effect of Melt Purification Treatment on the Solidified Microstructure of Hypereutectic Al-Si Alloys

Microstructure and Mechanical Properties of Hypereutectic Al-Si Alloys Subjected to Magnetodynamic Treatment

Microstructure and Mechanical Properties of Hypereutectic Al-Si Alloys Subjected to Magnetodynamic Treatment

Enhancing the tensile strength of SiC reinforced aluminium-based functionally graded structure through the mixture design approach

PurposeThis article aims to study the tensile properties of a functionally graded composite structure with Al–18wt%Si alloy as the matrix material and silicon carbide (SiC) particles as the reinforcing element. More specifically, the study's primary objective is to optimize the composition of the material elements using a robust statistical approach.Design/methodology/approachIn this research, the composite material is fabricated using a combination of stir casting and the centrifugal casting technique. Moreover, the test specimen required to study the tensile strength are prepared according to the ASTM (American Society for Testing and Materials) standards. Eventually, optimal composition to maximize the tensile property of the material is determined using the mixture design approach.FindingsThe investigation results imply that the addition of the SiC plays a crucial role in increasing the tensile strength of the composite. The optical microstructural images of the composite show the adequate distribution of the reinforcing particles with the matrix. The proposed regression model shows better predictability of tensile strength. In addition, the methodology aids in optimizing the mixture component values to maximize the tensile strength of the produced functionally graded composite structure.Originality/valueLittle work has been reported so far where a hypereutectic Al–Si alloy is considered the matrix material to produce the composite structure. The article attempts to make a composite structure by using a combination of stir casting and centrifugal casting. Furthermore, it employs the mixture design to optimize the composition and predict the model of the study, which is one of a kind in the field of material science.

Influence of characteristic eutectic free microstructure on mechanical and corrosion response of spark plasma sintered hypereutectic Al-Si alloy

Spark plasma sintered hypereutectic Al-Si alloy, free from characteristic eutectic microstructure was evaluated for its mechanical and corrosion behaviour in comparison with conventional cast microstructure having coarser primary Si and acicular eutectic Si. In SPSed microstructure, Al region free from acicular eutectic imparts substantial failure strain under compression loading. Absence of coarser primary Si and acicular eutectic Si in SPSed microstructure prevents the rate of anodic dissolution, specifically at the Al-Si interface and enhances corrosion resistance than the cast microstructure in 3.5 wt% NaCl corrosive medium.

Crack configuration feature and fracture surface difference for high pressure die casting hypereutectic Al-Si alloys in high cycle fatigue

Fatigue crack surfaces for three high pressure die casting hypereutectic Al-Si alloy plates were characterized by synchrotron X-ray tomography and CT technology. Focused on the retained pores, microvascular network analyses offered an innovative method to obtain crack configuration feature and analyze the crack propagation behavior in low ductility hypereutectic alloys which in-situ experiments were hard to achieve. With more Si content, the crack local thickness difference along the crack propagation path was more obvious and laid the foundation for more local tortuous morphology. With less Si content, the crack size was tapered and more branches occurred as a way to elongate the crack length. As rigid phases in the microstructure, primary silicon particles worked as obstacle for the whole crack propagation and their volume content agreed with the overall crack fluctuation. Therefore, the difference of flat propagation surface in three alloys was explained by crack configuration difference and crack deflection based on PSPs obstacle effect.

High temperature wear micromechanisms in Al–17Si–5Cu alloy after an isothermal heat treatment

ABSTRACT The present investigation deals with the wear micromechanisms in hypereutectic Al–Si alloy containing Cu (AR alloy) after an isothermal heat treatment developed by the present authors. The heat-treated alloy (HT alloy) is subjected to a dry sliding wear test in a rotary tribometer under various loads against a hardened steel disk. Tests are conducted at higher temperatures, viz., at 200°C and 300°C. Worn surfaces and wear debris are characterised in the scanning electron microscope and X-ray diffractometer to find out wear mechanisms. The study reveals that severe wear occurs in the case of AR alloy at higher temperatures due to accelerated wear processes. On the other hand, HT alloy exhibits less wear due to resistance to wear in HT alloy. This improvement in wear behaviour in HT alloy is explained by the micromechanisms of wear.