Surface Friction Coefficient Research Articles

Numerical study of melting heat transfer in stagnation-point flow of hybrid nanomaterial (MWCNTs+Ag+kerosene oil)

PurposeThe purpose of this study is to analyze hybrid nanofluid (MWCNTs+Ag+Kerosene oil) over a stretched cylinder. Flow analysis is carried out in presence of stagnation-point. Features of heat transport are examined via melting conditions.Design/methodology/approachGoverned expression (partial differential equations) for flow and heat transfer are transmitted into ordinary differential equations (ODEs) via applying adequate transformations. For solutions development shooting method (bvp4c) is used on these non-linear coupled ODEs.FindingsComparative observation among hybrid nanofluid (MWCNTs+Ag+Kerosene oil), basefluid (kerosene oil) and nanofluid (MWCNTs+Kerosene oil) are performed. Influences of physical parameters on heat transfer rate, velocity, skinfriction coefficient and temperature are visualized graphically. Higher values nanoparticle volume fractions, curvature parameter, melting parameter and velocity ratio parameter lead to intensification in the velocity profile. The temperature of the fluid reduces with higher values nanoparticle volume fractions, curvature parameter and melting parameter. The surface friction coefficient is minimized via a higher melting parameter and velocity ratio parameter. Heat transmission rate intensifies with velocity ratio parameter, nanoparticle volume friction and curvature parameter while it reduces gradually with larger melting parameter. During comparative study performance of hybrid nanomaterial (MWCNTs+Ag+Kerosene oil) is outstanding and is proceeded by nanomaterial (MWCNTs+ Kerosene oil) and basefluid (kerosene oil).Originality/valueIn the presented study authors have analyzed the flow of hybrid nanomaterial (MWCNTs+Ag+Kerosene oil) by a stretching cylinder. The further cylinder is subjected to stagnation point and melting condition. The authors believe that all the consequences of the presented study and numerical technique (bvp4c) are original and not published before.

Influence of surface roughness, friction coefficient, and wrap angle on clinching joint strength and its correlation with belt friction phenomenon

Clinching is an economical sheet joining technique that does not require any consumables. Besides, after its usage, the joints can be recycled without much difficulty, making clinching one of the most sustainable and eco-friendly manufacturing processes and a topic of high research potential. In this work, the influence of surface roughness on the load-bearing capacity (strength) of joints made by the mechanical clinching method in cross-tensile and lap-shear configuration is explored. Additionally, a correlating mathematical model is established between the joint strength and its surface parameters, namely, friction coefficient and wrap angle, based on the belt friction phenomenon. This correlation also explains the generally observed higher strength in lap-shear configuration compared to cross-tensile in clinching joints. From the mathematical correlation, through friction by increasing the average surface roughness, it is possible to increase the strength of the joint. The quality of the thus produced joint is analyzed by cross-sectional examination and comparison with simulation results. Experimentally, it is shown that an increment of >50% in the joint strength is achieved in lap-shear configuration by modifying the surface roughness and increasing the friction coefficient at the joint interface. Further, the same surface modification does not significantly affect the strength in cross-tensile configuration.

An Investigation in Wear and Friction of Oil Seal for Rubbing by Flame-Sprayed Alloy and Ceramic on Lower Carbon Steel

In this paper, the effect of sprayed coating on the surface of carbon steel on friction and abrasion properties of oil seals which are rubbed by various anti-wear coating materials on is investigated experimentally, and compared with the uncoated AISI 52100 bearing steel. We used the block vs ring tester to explore the friction coefficient of hard surface friction of 5 commonly used rubber seal to 4 different coating layers of bearing steel under oil/no oil conditions. Four coating materials are used, which are Ni-Cr-B-Si alloy, Ni-Cr-WC alloy, ceramics, and ceramics. Five varieties of the oil seal material named HNBR, NBR, FKM, ACM, and SIL are subjected to wear tests for the measurements of friction and abrasion. The experimental results show that HNBR has better wear resistance and less friction, ceramics have higher friction and wear resistance than other coatings due to higher hardness. In terms of oil seal and sprayed coating, Ni-Cr-B-Si alloy and ceramic powder are more suitable for surface wear resistance, because of its hardness and wear resistance and the degree of damage to the oil seal are more excellent. Generally, the greater the wear resistance of the oil seal material, the greater its friction with the coating.

Movement process analysis of the high-speed long-runout Shuicheng landslide over 3-D complex terrain using a depth-averaged numerical model

Flow-like landslide is one of the most catastrophic types of natural hazards due to its high velocity and long travel distance. In 2019, a large catastrophic landslide was triggered by heavy rainfall and occurred in Shuicheng County, Guizhou, China. The Shuicheng landslide was characterized by a short slip time, high speed, and long sliding distance, causing significant damages to the downstream communities and properties. Depth-averaged models have been widely used to predict the velocity and runout distance of flow-like landslides. However, most of the existing depth-averaged models have various shortcomings for application in real-world simulations. In this study, a high-performance depth-averaged model taking into account the effects of topography-related vertical acceleration and centrifugal force was used to examine the influence of complex 3-D terrain on the landslide movement process. The simulation results were in satisfactory agreement with the field observations. This work reveals the landslide movement process at different stages, including acceleration, diversion, secondary acceleration, impact, and deposition. The maximum average velocity was predicted to be 35 m/s, with a local maximum velocity exceeding 50 m/s. The seismic records obtained from the adjacent seismic stations and the predicted kinetic energy and velocity of the landslide event revealed a dual acceleration and obstruction process. It was also found that the movement process and final deposit morphology were strongly influenced by the complex terrain and were sensitive to the surface friction coefficient. This may also be the reason for the survival of some houses in the middle of the slope during the event. This study provides a reference for investigating long-runout, high-speed, flow-like landslides.

The Influence of Forefoot Bending Stiffness of Futsal Shoes on Multiple V-Cut Run Performance.

A forefoot bending stiffness (FBS) property of footwear is known to benefit athletes in running performance. To date, the efficacy of bending stiffness on performance is rather unknown from the perspective of futsal shoes. This study investigates the influence of bending stiffness property of three commercial futsal shoes on change of direction run resultant performance. Nineteen university level athletes participated in the human performance test (multiple V-cut change of direction run) on a hardwood flooring facility using three pairs of futsal shoes (i.e., S1, S2, and S3) with different models but similar in outsole material (S1—mass: 311 g, heel-to-toe drop: 10 mm, friction coefficient, 1.25; S2—mass: 232 g, heel-to-toe drop: 8 mm, friction coefficient: 1.34; and S3—mass: 276 g, heel-to-toe drop: 7 mm, friction coefficient: 1.30). The FBS properties for each shoe were mechanically measured. Results from the analysis of variance indicated that there was a significant difference of FBS value among the three shoes (S1: 0.32 Nm/deg., S2: 0.26 Nm/deg., and S3: 0.36 Nm/deg.) [F(2,8) = 28.50 (p < 0.001)]. Shoes with relatively higher shoe-playing surface friction coefficient (S2 and S3) had significant impact on the V-cut performance (p < 0.05) when compared with the shoe with lower friction coefficient (S1). In contrast to the literature, the shoe with the lowest FBS (S2) did not suffer any detriments on the resultant performance in the test conducted. These findings suggested that there could be other performance limiting factors, such as the friction coefficient, rather than FBS that have greater influence on the test outcomes.

Friction behavior of TiN–MoS2/PTFE composite coatings in dry sliding against SiC

To improve the dry friction behavior of traditional hard coatings, MoS2/PTFE lubricating coatings were prepared on the PVD TiN-coated cemented carbide using spray method. The influences of MoS2/PTFE lubricating coatings on the primary characteristics of TiN coatings were investigated. Reciprocating sliding tests were carried out with the TiN–MoS2/PTFE coated specimen (T-M-P) under dry sliding conditions, and the tribological behaviors were compared to those of the TiN-coated one (T-N). The test results indicated that the adhesion force of coatings with substrate for T-M-P specimen increased, the surface micro-hardness, roughness and friction coefficient significantly decreased. Meanwhile, the surface adhesions and abrasion grooves of T-M-P specimen were reduced, and the main wear forms of T-M-P were abrasion wear and coating delamination. The MoS2/PTFE lubricating coatings can be considered effective to improve the friction properties of traditional hard coatings.

Wind tides and surface friction coefficient in semi-enclosed shallow lagoons

The present paper is specifically focused on enclosed or semi-enclosed basins where the wind is the dominant driver of water surface tilting, leading to the so-called wind tide contributing to water levels rise. Wind-induced free surface tilting is studied using the 1-D steady form of the depth-averaged shallow water (Saint-Venant) momentum equation which reflects the depth-averaged local balance between surface slope and wind stress. Two contrasted field sites, the Berre and Vaccarès lagoons, have been monitored providing water level data along a reference axis. This study highlighted the occurrence of wind tides at the two field sites. The bimodal wind exposure ensured the robustness of the observations, with non-linear but symmetric behaviors patterns observed in winds from opposite directions. It is observed that the higher the wind speed, the steeper the slope of the free surface in accordance with the well known basic trend. In addition, a significant effect of depth is observed, with greater surface tilting in the shallower lagoon. The data analysis confirmed the robustness of such a simple approach in the present context. Using the additional assumption of constant, i.e. wind-independent, drag coefficients (CD) allowed a good match with the observations for moderate wind speeds for both sites. However, the depth effect required the CD to be increased in the shallower basin. Classical empirical wind-dependent CD parameterizations provide better wind-tide predictions than the constant-CD approach in very strong wind conditions but totally failed in predicting surface tilting in the shallower site, suggesting that physical parameters other than wind speed should be taken into account for the CD parameterization in very shallow lagoons.

Study of the micro/nano-texture design to improve the friction properties of DLC thin films

In this study, a DLC pattern was fabricated through a photolithography process that constitutes a part of the semiconductor process, to investigate the frictional wear characteristics. The photolithography was used to produce negative patterns with a pattern width of 10 [Formula: see text]m or 20 [Formula: see text]m and a pattern depth of 500 nm on the DLC surface. The change in the coefficient of friction of the surface was investigated through a ball-on-disk tribology test on the fabricated micro/nano-sized DLC pattern. The DLC pattern fabricated by the photolithography process showed a superior coefficient of friction to that of the general DLC sample. These results show that the decrease in the surface friction coefficient of the patterned DLC thin film is due to the reduction in the surface contact area owing to the modification of the micro/nano-texture of the surface as well as the low friction characteristics of the DLC.

Surface texture and friction property of Ti-6Al-4V processed by rotary ultrasonic rolling

Micro-texturing on machined surface has been widely applied to improve surface friction and wear properties. This paper aimed at establishing a relationship among process parameters, machined surface texturing, and friction property of scaly surface fabricated by rotary ultrasonic rolling. Firstly, a kinematic model of the scaly surface topography formation was proposed based on motion analysis between the roller and workpiece. Secondly, the roller profile was considered in the proposed model to describe the scaly surface topography formation. Three-dimensional surface roughness characteristic parameters Sa, Sz, and Sq were adopted to evaluate the scaly surface topography. These three-dimensional surface roughness parameters can be theoretically predicted with the proposed kinematic model for the scaly surface fabricated by rotary ultrasonic rolling of titanium alloy Ti-6Al-4V. The theoretical predictions of Sa, Sz, and Sq were verified with the experimental results. Finally, the friction coefficients of scaly surfaces generated with various rotary ultrasonic rolling parameters were tested. The friction coefficient of the scaly surface was minimum at ultrasonic amplitude of 7 μm. The results demonstrated that the surface texturing with larger scaly ridges possessed improved frictional performance under identical test conditions.

Textile Triboelectric Nanogenerators with Diverse 3D-Spacer Fabrics for Improved Output Voltage

Electrically superior triboelectric nanogenerators (TENG) using 3D fabric and PDMS show great application potential for biokinetic energy harvesting and multifunctional self-power devices. In this study, TENG with fabric-PDMS-fabric structure was produced using various 3D fabrics and PDMS. The peak-to-peak output voltage of various 3D fabrics was compared. The output voltage changes due to structure and vertical fibers. Also, the coefficient of surface friction between the PDMS and the fabric improves the output voltage. TENG using different 3D-spacer polymeric fabrics showed different maximum peak-to-peak output voltage performance. It is attributed to the stiffness, lateral elasticity and 3D morphology of the fabrics. It is considered that those factors including stiffness, lateral elasticity and 3D morphology influence the densities in vertical and lateral fiber to fiber interaction.

Influence of applied magnetic field on nonlinear mixed convective nanoliquid flow past a permeable rough cone

The concept of magnetohydrodynamic nonlinear mixed convective nanoliquid flow over a vertical rough cone finds applications in science and engineering fields, especially in aerospace and thermal engineering as well as in other designing and manufacturing processes. In the present investigation, the cone surface roughness, which arises during the manufacturing processes, is modelled using sine wave forms. A uniform magnetic field is applied to analyse its impact on the transport characteristics of the flow. The study of such flow problems involving physical parameters such as nonlinear convection, permeable roughness, nanoparticles and external magnetic field is an innovative approach. The flow problem is modelled using nonlinear coupled partial differential equations which are transformed into dimensionless form by using Mangler’s non-similar transformations. The resulting equations are solved by utilizing the quasilinearization technique in combination with the implicit finite difference scheme. Effects of the different physical parameters on profiles and gradients are analysed by the graphical representations. Findings show that the higher values of the nonlinear mixed convection parameter will increase nanofluid velocity and magnitude of the coefficient of surface friction. Prominent sinusoidal oscillations are found in the surface gradients away from the apex of the cone due to the surface roughness effects.

Rheology and tribology: investigating the migration of small molecules in recycled agricultural waste multilayer films

This paper deals with polyisobutylene (PIB) migration through post-consumer agricultural waste multilayer films based on four linear low-density polyethylene (LLDPE) matrices. Connections between shear, elongational rheology and tack surface properties were revealed for both model and recycled blends. The effects of aging time and temperature were investigated and rationalized, depending on the short- and long-chain branching in LLDPE matrices as well their polyethylene (PE) crystallization. Linear and nonlinear viscoelastic properties were influenced by even small amounts of PIB. This migration also influenced slippage in the steady-flow regime. Transient uniaxial extensional properties were shown to be very sensitive to the presence of PIB, which seems to hold back the PE strain hardening properties. Therefore, the axial force and the surface friction coefficient were determined and discussed in correlation with bulk rheological findings. These results help unveil new insights about the physical mechanisms governing PIB migration with or without fillers inhibiting this migration in recycled films.

Probabilistic Surface Friction Estimation Based on Visual and Haptic Measurements

Accurately modeling local surface properties of objects is crucial to many robotic applications, from grasping to material recognition. Surface properties like friction are however difficult to estimate, as visual observation of the object does not convey enough information over these properties. In contrast, haptic exploration is time consuming as it only provides information relevant to the explored parts of the object. In this work, we propose a joint visuo-haptic object model that enables the estimation of surface friction coefficient over an entire object by exploiting the correlation of visual and haptic information, together with a limited haptic exploration by a robotic arm. We demonstrate the validity of the proposed method by showing its ability to estimate varying friction coefficients on a range of real multi-material objects. Furthermore, we illustrate how the estimated friction coefficients can improve grasping success rate by guiding a grasp planner toward high friction areas.

Исследование течения флюида к горизонтальной скважине

Recently, it is necessary to note the presence of negative dynamics in the deterioration of the reserves structure for newly discovered fields, and most of the them are classified as hard-to-recover, confined to deposits with a complex geological structure, low permeability, high oil viscosity, complicated by the presence of faults, active bottom waters and gas caps. Hard-to-recover reserves are drilled with horizontal wells. This is primarily because horizontal wells make it possible to multiply the area of fluid filtration due to the increase in the drainage area, due to the extensive contact of the horizontal well section with the rock, allowing to increase the well flow rate many times over. Summarizing the above, horizontal wells are used to develop fields with the following parameters: fields with a thin oilsaturated rim (up to 15 m), with a gas cap and bottom water; fields of heavy oil, with a viscosity of more than 30 mPa·s; fields with low reservoir permeability (less than 0.002 μm2). Under these conditions, linear Darcy’s law cannot describe fluid filtration. Under the conditions of high-viscosity oil and lowpermeability reservoir existence, a certain initial pressure gradient is determined, due to the rheological properties of the filtering fluid and high values of the surface friction coefficient. Under conditions of a thin oil rim and an increased gas factor, the limiting filtration rates due to the dissolved gas regime are observed, and a nonlinear law describes the fluid inflow. One of the main parameters in the preparation of the technical and economic assessment of the reservoir is the flow rate of each individual horizontal well. Analytical methods for calculating the horizontal well flow rate show a high error. It is proposed to take a fresh look at the problem of determining the predicted flow rate of a horizontal well, using well-known approaches for solving this issue. It is rather difficult to reliably predict the parameters of reservoir operation: the horizontal wells productivity obtained with the help of modern hydrodynamic stimulators turns out to be unreliable, which leads to the formation of an insufficiently rational development system. And the arising complications during operation in field conditions have to be eliminated due to significant volumes of material and labor resources. Thus, the development of methods that contribute to obtaining a reliable calculation of production is an urgent task for the oil industry.

Prediction model of fractal dimensions in steady state through a multi-stage running in of Sn11Sb6Cu and AISI 1045 steel

Running in plays an important role in improving surface contact state, reducing friction and wear of main bearings in diesel engines. In practical application, multi-stage running in, through which load and speed are increased step by step, is used to improve the running-in quality and efficiency. Fractal dimensions of surface topography and friction coefficient were applied to characterize the quality. To predict the fractal dimensions, the multi-stage running in tests of bearing material Sn11Sb6Cu were performed. The prediction models were established by a response surface approach. The result of regression analysis reveals that the load and velocity of the first two stages is more important than other factors, while the running-in time of the first stage has no significant effect on the running-in quality. The established models provide the basis for appropriate choice of load, speed and duration time in each stage.

Influences of pulse frequency on formation and properties of composite anodic oxide films on Ti-10V-2Fe-3Al alloy

A thick composite anodic oxide film was fabricated in an environmentally friendly malic acid electrolyte containing PolyTetraFluoroEthylene (PTFE) nanoparticles on Ti-10V-2Fe-3Al alloys. The influence of pulse frequency on the morphology, microstructure and composition of composite anodic oxide films containing PTFE nanoparticles was investigated using Field Emission Scanning Electron Microscopy (FE-SEM) equipped with Energy Dispersive Spectroscopy (EDS), Atomic Force Microscopy (AFM) and Raman spectroscopy. The tribological properties in terms of the friction coefficient, wear loss and morphology of worn surfaces were measured by ball-on-disc tests. The electrochemical property was evaluated by potentiodynamic polarization. The results indicated that the titanium dioxide of composite anodic oxide films transformed from anatase to rutile with the change of pulse frequency, which could result from the electrochemical dynamic equilibrium. The combination of PTFE nanoparticles and malic acid electrolyte molecules can influence the energy fluctuation of electrochemical equilibrium and formation of composite anodic oxide films. Moreover, composite anodic oxide films fabricated under the condition of 1.0–2.0 Hz exhibited the best wear resistance and corrosion property. The schematic diagram of the film formation and PTFE nanoparticles spreading process under different frequencies was elucidated.

Enhancing the wear and oxidation behaviors of the Inconel 718 by low temperature aluminizing

Inconel 718 has a wide area of applications in gas turbines, aircraft, turbocharger rotor equipment, and so many other applications, including applications with temperatures up to ~700 °C. In this study, Ni-based aluminide coating on Inconel 718 alloy was applied by pack cementation technique. Phase structures, layer coating thickness, hardness, wear, and oxidation behaviors were studied for different aluminization temperatures and times (600 and 700 °C for 3 and 5 h). The change in the layer from the surface to the inside was varied from 8 to 80 μm and this was increased with higher aluminization temperature and more time. The hardness value of 960 HV was determined in the coating layer whereas the hardness of the matrix was 260 ± 10 HV. The wear resistance of the samples was tested under dry sliding conditions with different loads. The wear resistance of Inconel 718 has increased with aluminization. Increased aluminization duration and temperature reduced wear losses. Isothermal oxidation test results at 1000 °C for 5, 25, and 125 h show that Inconel 718 has a poor oxidation resistance under these conditions while aluminized Inconel 718 samples exhibit better results. The comparison of the aluminized Inconel 718 samples after oxidation tests showed that the aluminization at higher temperatures allowed the formation of a compact and continuous alumina layer while the formation of porosities under the oxide scale weakened the adherence and durability in the others. • The Inconel 718 was subjected to low temperature aluminizing at different temperatures and times. • Microstructure, wear and oxidation properties of Inconel 718 and coatings were investigated. • Aluminization improved the wear and oxidation properties of the Inconel 718 alloy. • With the increasing surface hardness, wear losses and friction coefficient decreased. • The formed Ni Al rich phases enable the formation of alumina phases during the oxidation tests.

Experimental and Numerical Investigation of the Micro-Crack Damage in Elastic Solids by Two-Way Collinear Mixing Method.

This study experimentally and numerically investigated the nonlinear behavior of the resonant bulk waves generated by the two-way collinear mixing method in 5052 aluminum alloy with micro-crack damage. When the primary longitudinal and transverse waves mixed in the micro-crack damage region, numerical and experimental results both verified the generation of resonant waves if the resonant condition was satisfied. Meanwhile, we found that the acoustic nonlinearity parameter (ANP) increases monotonously with increases in micro-crack density, the size of the micro-crack region, the frequency of resonant waves and friction coefficient of micro-crack surfaces. Furthermore, the micro-crack damage in a specimen generated by low-temperature fatigue experiment was employed. It was found that the micro-crack damage region can be located by scanning the specimen based on the two-way collinear mixing method.

A new approach to evaluate material creep properties by C-shape ring specimen with fixed constraints

Small specimen test technique is widely used to evaluate material creep properties for those components operated at the elevated temperatures. However, the existing small specimen test techniques cannot be well applied for small miniature tubular components well, such as steam pipe and gas turbine recuperator in aviation, due to the equivalent gauge length, specimen volume, stress analysis method and conversion relationship. In this paper, combing the advantages of three-point bending specimen with fixed constraints and small ring creep specimen, a new C-shape ring specimen with fixed constraints (CRSFC) was proposed. Based on beam bending model, the conversion relationship between CRSFC and uniaxial creep test data was established by using complementary strain energy and reference stress method. Using finite element method, conversion coefficients and stress evolution process were obtained. Then the feasibility and accuracy of the above conversion relationship were verified by carrying out four sets of CRSFC creep tests of 1.25Cr0.5MoSi at 550 °C. It can be seen that creep parameters obtained by CRSFC agree well with those from uniaxial creep test with the maximum error of 22.6%. Finally, the effects of the straight edge length, indenter radius, eccentric load and indenter-specimen surface friction coefficient on the load-point steady-state displacement rate were investigated by finite element method. The results show that the effect of the straight edge length is negligible. In order to minimize the effects of other parameters, the indenter radius 0.6 mm ≤ r ≤ 1.2 mm, eccentric displacements e ≤ 0.2 mm and friction coefficient f ≤ 0.8 are recommended in CRSFC creep test.

The Effect of High-Intensity Electron Beam on the Crystal Structure, Phase Composition, and Properties of Al–Si Alloys with Different Silicon Content

The study deals with the element–phase composition, microstructure evolution, crystal-lattice parameter, and microdistortions as well as the size of the coherent scattering region in the Al–10.65Si–2.11Cu and Al–5.39Si–1.33Cu alloys irradiated with the high-intensity electron beam. As revealed by the methods of x-ray phase analysis, the principal phases in untreated alloys are the aluminium-based solid solution, silicon, intermetallics, and Fe2Al9Si2 phase. In addition, the Cu9Al4 phase is detected in Al–10.65Si–2.11Cu alloy. Processing alloys with the pulsed electron beam induces the transformation of lattice parameters of Al–10.65Si–2.11Cu (aluminium-based solid solution) and Al–5.39Si–1.33Cu (Al1 and Al2 phases). The reason for the crystal-lattice parameter change in the Al–10.65Si–2.11Cu and Al–5.39Si–1.33Cu alloys is suggested to be the changing concentration of alloying elements in the solid solution of these phases. As established, if a density of electron beam is of 30 and 50 J/cm2, the silicon and intermetallic compounds dissolve in the modified layer. The state-of-the-art methods of the physical materials science made possible to establish the formation of a layer with a nanocrystalline structure of the cell-type crystallization because of the material surface irradiation. The thickness of a modified layer depends on the parameters of the electron-beam treatment and reaches maximum of 90 µm at the energy density of 50 J/cm2. According to the transmission (TEM) and scanning (SEM) electron microscopy data, the silicon particles occupy the cell boundaries. Such changes in the structural and phase states of the materials response on their mechanical characteristics. To characterize the surface properties, the microhardness, wear parameter, and friction coefficient values are determined directly on the irradiated surface for all modification variants. As shown, the irradiation of the material surface with an intensive electron beam increases wear resistance and microhardness of the Al–10.65Si–2.11Cu and Al–5.39Si–1.33Cu alloys.