Hypereutectic Al-Si Alloys Research Articles

Grain-refining mechanism in hypereutectic Al-20Si alloy with minor Sr - Sc - La and ultrasonic vibration treatment

The grain-refining mechanism with minor Sr - Sc - La and ultrasonic vibration treatment (UVT) in the hypereutectic Al-20Si alloy were studied. The results demonstrated that the microstructure of the hypereutectic Al-20Si alloy could be refined significantly, further improve its mechanical properties. The desirable refinement of the microstructure was achieved using 0.2% Sr, 0.15% Sc, and 0.3% La under UVT, achieving the highest grain circularity coefficient, hardness, elongation, and area reduction. The tensile strength was the largest with the addition of 0.2% La. The findings of this study provide theoretical and experimental guidelines for the fabrication of structural materials for application in automotive, aerospace, and deep-sea equipment.

Fabrication of hypereutectic Al–Si alloy with improved mechanical and thermal properties by hot extrusion

Silicon phase in hypereutectic AlSi powders appears as primary Si and eutectic Si. Due to the poor thermal stability of eutectic Si, the material suffers from pores, stress concentration and dislocation packing during hot extrusion process, resulting in low density and poor thermal properties. In order to eliminate the eutectic Si, a heat treatment is conducted on Al20Si powders before hot extrusion. Because of the Ostwald ripening effect, the eutectic Si and dislocations in the powders are replaced by isolated Si lumps and a clear Al matrix. As a result, the formability and thermal properties of the material are greatly improved. The extruded samples made from the treated powder present high relative densities 99.7–100%, ultimate tensile strength (UTS) 167–170 MPa, elongations 8.8–10.8% and thermal conductivities (TCs) 191–195 Wm−1 K−1 and low coefficient of thermal expansions (CTEs) 13.8–14.5 × 10−6/K. The excellent mechanical and thermal properties are attributed to the elimination of eutectic Si from the treated powders and as-extruded alloys. In addition, hot extrusion introduces in-situ Al2O3 in the Si surface, Al grain boundary and Al grains, which is beneficial to reducing and stabilizing the CTE of the material. Moreover, it hinders Ostwald ripening and thus growth of the Si particles during the service of the material.

Synergistic Effect of Lanthanum and Melt Purification on the Microstructure of Hypereutectic Al–Si Alloy

Synergistic Effect of Lanthanum and Melt Purification on the Microstructure of Hypereutectic Al–Si Alloy

Improving Mechanical Property of Hyper-Eutectic Al-Si Alloys via Regulating the Microstructure by Rheo-Die-Casting

The microstructure plays a key role in the mechanical properties of hyper-eutectic Al-Si alloys. In this study, we investigate the microstructural evolution of rheo-die-casting (RDC) on the Al-15Si-4Cu-0.5Mg alloy using a mechanical rotational barrel system. Our findings demonstrate that higher rotational speed and pouring temperature reduce the size and roundness of primary Si particles in the semisolid slurry. Additionally, during RDC, the dendritic aluminum matrix and skeletal iron-containing inter metallics are sheared off, leading to a more uniform and dispersed Al2Cu phase. Ultimately, our rheo-diecasting results indicate the formation of a near globular aluminum matrix, fine primary Si particles, and a homogeneous Al2Cu phase, thus highlighting the efficacy of this processing method for improving the microstructure and properties of the Al-15Si-4Cu-0.5Mg alloy. We suggest that these results hold promise for enhancing the quality of aluminum-based alloys in various industrial applications.

Multi-Phase Structure Control and Interfacial Investigation of TiB2/Hypereutectic Al-Si Alloy

The effect of the distribution of the primary phase Si and TiB2 particles in the hypereutectic Al-Si alloy was studied and found to be influenced by the cooling rate. Therefore, this article studies the effect of the cooling rate on the multi-phase structure of TiB2 particles in Al-20Si using a wedge-shaped mold. The sizes, shapes, and distribution of primary phase Si and TiB2 particles inside primary phase Si were observed through SEM. The effect of TiB2 particles on cracks in primary phase Si was studied using nanoindentation technology, and the interface relationship between primary Si and TiB2 was studied using TEM. Finally, based on the experimental results, the trapping mechanism of primary Si for TiB2 particles is discussed. The results indicate that the faster the cooling rate, the finer and more uniform the size distribution of the primary Si phase in the structure. TiB2 mostly exists as individual particles. Moreover, the pushing rate of the solid–liquid interface during solidification is faster, resulting in more TiB2 particles being engulfed by the primary Si phase.

Effect of melt purification treatment on the solidified microstructure of hypereutectic Al-Si alloys

In this paper, hypereutectic Al-Si alloys were purified by a composite sodium salt, and the solidified microstructure of hypereutectic Al-Si alloys before and after melt purification was studied by OM, SEM/EDS, XRD, and TEM. The results showed that the Fe content decreased from 0.73 wt% to 0.23 wt% after purification with the Na salt. This also prevented an increase in heterogeneous nucleation. The Si content remained almost unchanged, which excluded the possibility of removing Si from the molten Na salt. According to DSC analysis, Na salt purification increased the undercooling degree of the melt, so that the hypereutectic Al-Si alloy melt was deeply undercooled to the pseudo eutectic region, and a nearly-perfect pseudo eutectic structure was obtained. Moreover, it was confirmed that NaAlSi changed the growth of eutectic Si, thereby changing its microstructure. At the same time, nanoscale spherical precipitates formed by trace Fe in the alloy could significantly promote the nucleation of eutectic Si.

INFLUENCES OF P AND Sr ON MICROSTRUCTURE AND ITS EFFECTS ON MACHINABILITY AND MECHANICAL PROPERTIES OF HYPEREUTECTIC Al-20%Si

Hypereutectic Al-Si alloys are widely utilized in the automotive industry due to their high strength-to-weight ratio, minimal thermal expansion, and superior castability. The downside of hypereutectic Al-Si alloys is the formation of coarse primary silicon particles. The primary Si phases were controlled by the growth-hindering agents, phosphorus (refiner), and strontium (modifier) by using a conventional stir casting technique at room temperature. The microstructural changes were observed through an optical microscope and SEM analysis. The additions of 0.08% P have ensured the formation of the uniformly distributed fine-grained particles in the alloy. The primary silicon particle size was reduced from 220[Formula: see text][Formula: see text]m to 150[Formula: see text][Formula: see text]m as compared to the untreated alloy. The tensile and yield properties of the treated alloy were increased by 12.7% when compared to the untreated alloy with a hardness of 131 BHN. The treated alloy imparted better impact toughness, ensuring a ductile mode of failure through the fractography studies. The influence of the microstructure on the machinability of the alloy was investigated in a dry environment with uncoated and coated inserts (code: CCGT 09T304 FL K10) by varying the process parameters, i.e. speed, feed rate, and depth of cut (DoC). Modification of the primary and eutectic Si phases of an Al-20Si hypereutectic alloy increases machinability with coated inserts as well as its mechanical properties.

Microstructure and Tribological Property Correlations of Die Cast and Spray Formed Al-30 wt.% Si Alloy

Al-30 wt.% Si hypereutectic alloy was produced by die casting and spray forming technique. The microstructures, mechanical and tribological properties of the alloy were studied. The density of die cast and spray formed samples are measured using water displacement method by applying the Archimedes principle. The scanning electron micrographs of die cast and spray formed alloys revealed the morphological changes of silicon phase from coarse silicon needles to fine silicon needles due to high undercooling encountered in spray forming. The size of the hard silicon platelets are decreased from 22 µm to less than 10 µm as the processing method is changed from die casing to spray forming. The average Vickers micro hardness of die cast and spray formed alloy are 70.06±2.65 HV and 78.05±2.01 HV respectively. The respective yield strengths of die cast and spray formed alloy are 130±9MPa and 150 ±7 MPa and the compression strengths are 251±11.6 MPa and 283±6.32 MPa. The precipitation strengthening mechanism is found to be involved in spray formed alloy.

Growth of Si particles and Al dendrites during solidification of a hypereutectic Al-Si-Cu alloy

Hypereutectic Al-Si alloys containing up to 16-20 wt% Si and often several wt% Cu are widely applied in automobile and aerospace industry, because of their high wear resistance and high-temperature resistance. The mechanical and physical properties of these alloys are strongly influenced by the size and morphology of the primary silicon particles. Here, rod-like bulk samples of hypereutectic Al-18wt%Si-10wt%Cu alloys were solidified in a Bridgman-Stockbarger furnace with different solidification parameters. Microstructure analysis of longitudinal and radial cross-sections demonstrated nearly equiaxed growth of Silicon particles in the 3D samples. At low cooling rate a few but larger Si particles exist compared to many and smaller Si particles for solidification with higher cooling rate. Also the structure of the Al dendrites is much finer at higher cooling rates. Additionally, sheet-like samples were solidified under isothermal cooling conditions. A real-time observation method using X-ray radiography allowed for the in-situ observation. During cooling down below the liquidus temperature, facetted Si particles are the first to nucleate. Reaching the nucleation temperature of Al, growth of non-facetted Al dendrites was observed simultaneously in the whole melt, generally not starting from the surface of existing Si particles. Some Al dendrites growing in the plane of the sheet-like samples develop rather rapidly in one direction, whereas other Al dendrites grow more equiaxed, which is attributed to different grain orientations of the Al-rich dendrites in quasi-2D solidification.

Synthesis of nickel coated graphene and analysis of the efficacy of its reinforcement on the hyper eutectic AlSi alloys that are grain modified and refined

Investigation on the impact of grain refiners and modifiers on the mechanical characteristics of Aluminium Silicon alloys is an ongoing subject. It is understood that the mechanical properties of AlSi alloys can be significantly improved by refining and modifying the grains and by adding the solid lubricants. In the present work, synthesis of nickel coated graphene particles is carried out. The die cast hyper eutectic AlSi alloys are subjected to grain refinement and modification with simultaneous reinforcement of nickel coated graphene powder. Nickel coated graphene particles are synthesised by electroless plating. After graphene is pre-treated, electroless plating was conducted in a bath having nickel nitrate as source of nickel along with sodium borohydrate as a reducing agent. During this procedure, ultrasonic agitation was used to improvise the coating properties. The coated graphene powder was characterised by EDAX which revealed the Ni coating on the surface of graphene. AlSi alloys of three distinct compositions are synthesised using die casting method. The first alloy comprises of aluminium silicon as the base alloy. The second alloy comprises of the nickel coated graphene reinforced aluminium silicon alloy. The third alloy comprises of aluminium silicon alloy which is grain refined, modified and further reinforced with the nickel coated graphene powder. The three different compositions of AlSi alloys thus casted, are tested for the mechanical properties like tensile strength and Vicker's hardness test. They are also tested for the microstructure by scanning electron microscopy and optical microstructure. The tensile strength and hardness are the highest for that alloy that is simultaneously grain refined, modified and nickel coated graphene reinforced. The microstructure of the third alloy displayed a clear transition of the plate like silicon to globular shaped eutectic silicon with uniformly distributed graphene. • Synthesis of Nickel coated Graphene powder (NCG). • Examine the coating of Nickel on the Graphene. • Preparation of the metal composites by die casting the Aluminium Silicon alloys. • Study the properties of alloys prepared using grain refiners, modifiers and NCG. • Report the tensile, micro hardness values and microstructure of the casted alloys.

Microstructure Evolution Characteristic and Control of Iron-Rich Phase in Hypereutectic Al–Si Alloy with Co, Mn and P

Microstructure Evolution Characteristic and Control of Iron-Rich Phase in Hypereutectic Al–Si Alloy with Co, Mn and P

Effects of AlCrFeNiTi HEA Addition on Microstructure and Mechanical Properties of Hypereutectic Al–20Si Alloy

Effects of AlCrFeNiTi HEA Addition on Microstructure and Mechanical Properties of Hypereutectic Al–20Si Alloy

The Effect of Tin on Microstructure and Properties of the Al-10 wt.% Si Alloy.

In this paper, the results from studies regarding near-eutectic Al-Si alloys with Sn as an alloying addition are presented. In most Al-Si alloys, tin is regarded as a contaminant; thus, its amount is limited to up to 0.3 wt.%. The few studies that can be found in the literature regarding the behaviour of tin in aluminium alloys suggest the beneficial effect of this element on selected properties. However, these results were obtained for hypereutectic Al-Si alloys or wrought aluminium alloys. In our studies, the influence of tin contents of up to 1.7 wt.% was determined on the AlSi10 alloy. Thermal analysis, measurements of the mechanical properties of the cast and heat-treated alloy, metallographic observations (light microscopy, scanning electron microscopy), and EDS (X-ray energy dispersive spectrometry) measurement allowed us to fully describe the effect of tin on the aluminium alloy. The results of the thermal analysis showed changes in the range of the α-Al solution crystallisation and the α+β eutectic through a decrease in the alloy’s solidification start point and eutectic solidification point. As a result, the elongation of the alloy was more than double in the AlSi10Sn1.7 alloy, with an A5 value of 8.1% and a tensile strength that was above 200 MPa.

Microstructural Modification Hardness and Surface Roughness of Hypereutectic Al-Si Alloys by a Combination of Bismuth and Phosphorus

This research aimed to investigate the effects of bismuth (Bi) and phosphorus (P) addition on the microstructure and roughness of a B390 hypereutectic Al-Si alloy. Microstructural variation of as-cast alloys showed that P is an effective refiner of primary Si and its distribution, while Bi has the opposite effect. The liquidus temperature increased with greater amounts of P, resulting in a wider solidification range. The solidus temperature increased with Bi content, resulting in a shortened solidification range. The benefit of Bi on eutectic silicon was through changing its morphology from fibrous to lamellar structures. It was observed that both primary Si and eutectic Si were modified when both P and Bi were added to the alloys. For effective refinement, the size of primary Si can be reduced by 50.6% and, the P content should not be less than 0.1 wt% with a Bi content of 0.5–1.0 wt%. Furthermore, an intermetallic phase size reduction also occurs. P addition results in a significant (5.85%) increase in hardness. Adding Bi (up to 1.0 wt%) together with P (up to 0.1 wt%) did not reduce the effect of P on the hardness of the modified alloys. The most effective reduction in roughness achieved during cutting at both low and high speeds was 26.5% and 57.7%, respectively, from modifying the B390 alloy using 0.1 wt%P with 1.0 wt%Bi.

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

"Influence of spark plasma sintering and conventional sintering on microstructure and mechanical properties of hypereutectic Al-Si alloy and hypereutectic Al-Si/B4C composites "

"Influence of spark plasma sintering and conventional sintering on microstructure and mechanical properties of hypereutectic Al-Si alloy and hypereutectic Al-Si/B4C composites "

Segregation behavior of primary phase within hypereutectic Al-Si alloy under electromagnetic levitation

针对电磁悬浮条件下过共晶Al-18at.%Si合金凝固组织中初生 (Si) 相的表层偏聚现象，结合有限元方法对悬浮液滴温度场和流场进行研究，旨在揭示初生 (Si) 相偏聚的物理机制。结果表明，Al-Si合金熔体在冷却过程中温度梯度和反向双涡流状流场是初生 (Si) 相在样品表层偏聚的主要因素，进而导致悬浮样品内部Si含量降低。同时，随初生 (Si) 相偏聚现象的加剧，内部形成共晶 (Si) 相形貌从针状转变为球状和短棒状。此外，在有限元计算中引入示踪粒子模拟了不同尺寸粒子在Al-Si合金熔体中的运动，并结合实验，发现不同粒径的初生 (Si) 颗粒均向样品表层迁移，粒径越大所需迁移时间越短。进一步地，对悬浮凝固样品显微硬度进行研究，发现由于初生 (Si) 相的表层偏聚使得样品表层具有超高硬度，约为内部显微硬度的13倍，从而提供了一种制备外硬内韧复合材料的新途径。

Effect of EMS Process on the Primary Si Refinement, Tensile and Fatigue Properties of Hyper-eutectic Al-15wt.%Si Alloy

This study investigated the effect of the electromagnetic stirring (EMS) process on the microstructure and mechanical properties of hyper-eutectic Al-15 wt.%Si alloy. The tensile and high-cycle fatigue properties of the EMS Al-15wt.%Si alloy were examined and compared with conventional direct chill (DC) cast alloy. The initial microstructure of the as-cast DC alloy showed a coarse primary Si of 70 µm, in contrast to the size (40 µm) of the as-cast EMS alloy. The DC extruded alloy exhibited a massive primary Si size of 40~55 µm. In contrast, the EMS extruded alloy had a spherical primary Si with 30~40 µm sizes. The average grain sizes were measured to be 8.8 µm (EMS extruded alloy) and 11.4 µm (DC extruded alloy), respectively. The EMS process was confirmed to contribute to the refinement of the grain size and the primary Si size of the hyper-eutectic Al-Si alloy. The yield strengths at room temperature were measured to be 388.0 MPa (EMS extruded alloy) and 375.0 MPa (DC extruded alloy), and the tensile strengths were 426.0 MPa (EMS extruded alloy) and 412.4MPa (DC extruded alloy), respectively. The elongations of both alloys were similar at room temperature. The fatigue limit of the EMS extruded alloy (130 MPa) was higher than that of the DC extruded alloy (120 MPa). The EMS extruded alloy exhibited superior fatigue resistance compared to the DC extruded alloy, regardless of the cyclic stress condition. This study also discussed the potential value of the EMS process as a method for improving the properties of hyper-eutectic Al-Si alloy, as well as the deformation and fracture mechanisms of the EMS Al-15wt.%Si alloy.

Highly ductile hypereutectic Al-Si alloys fabricated by selective laser melting

In the endeavor to maximize the refinement effect of primary Si and alleviate the inherent brittleness of hypereutectic Al-Si alloy, the approach of coating P as a modifier on powder was adopted. The ultimate aim was to create more heterogeneous fine AlP nucleus and enhance the nucleation efficiency of primary Si on AlP to refine the coarse primary Si to nano-scale during 3D printing. In the combination of large undercooling and high density of nucleation sites, the size of primary Si was successfully refined to 200–300 nm and the divorced eutectic was also induced to modify the microstructure of matrix. In the presence of nano-scale primary Si, the melting pool boundary (MPB) feature disappeared and the fracture mechanism also changed from load transfer to interfacial fracture. Compared with the pristine alloy, the ductility was increased four times without significantly changing the ultimate tensile strength (UTS) and wear resistance. The improvement of ductility is attributed to the refinement of primary Si, the disappearance of MPB features and the formation of divorced eutectic. The optimal tensile properties were: UTS-482 MPa, yield strength-320 MPa and ductility of 8.1% at 0.05 wt.% P. These are comparable to those for high-strength Al alloys.

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.