Eutectic Silicon Phase Research Articles

Effect of synergistic action of ultrasonic vibration and solidification pressure on tensile properties of vacuum counter-pressure casting aluminum alloy

The effect of synergistic action of ultrasonic vibration and solidification pressure on tensile properties of vacuum counter-pressure casting ZL114A alloys was studied systemically through testing and analyzing the tensile strength and elongation subjected to different ultrasonic powers and solidification pressures. The results indicate that the synergistic action of ultrasonic vibration and solidification pressure can result in the refinement of grains and improvement of tensile properties. Both the highest tensile strength and elongation of aluminum alloy were obtained under synergistic action of 600 W ultrasonic power and 350 kPa solidification pressure. Moreover, the tensile fracture morphology shows obvious ductile fracture characteristics. When the solidification pressure is lower than 300 kPa, the effect of ultrasonic power on tensile strength and elongation is more obvious, but when the solidification pressure is higher than 300 kPa, the effect of solidification pressure on tensile strength and elongation is greater. Meanwhile, the size and morphology of the eutectic silicon were improved significantly by the ultrasonic vibration and pressurized solidification. The strip and massive eutectic silicon phase are completely converted into small short rod-like and evenly distributed Si phases at the grain boundary of primary α-Al.

Optimized Segmentation of the 3D Microstructure in Cast Al-Si Piston Alloys

Abstract The thermomechanical behavior of cast Al-Si piston alloys is highly dependent on the condition of the highly interconnected hybrid 3D network which is composed of primary and eutectic silicon and intermetallic phases which are found embedded in the α-Al matrix. The very similar X-ray absorption of silicon and the α-Al matrix is problematic for the local identification of these phases and thus for the accurate segmentation and characterization of all rigid phases in the network when laboratory X-ray tomographs are used. A combination of conventional X-ray computed tomography, synchrotron computed tomography, and chemical deep etching performed on the same alloy and at the same position allows for an automatic segmentation and a more accurate characterization of phases across large representative volumes and thus provides the information necessary for a quantification of the whole 3D microstructure of the alloys.

Effects of Mn addition on microstructure and hardness of Al-12.6Si alloy

In this work, eutectic Al-12.6Si alloy with and without manganese (Mn) have been developed through gravity casting route. The effect of Mn concentration (0.0 wt.%, 1 wt%, 2 wt% and 3 wt%) on microstructural morphology and hardness property of the alloy has been investigated. The eutectic Al-12.6 Si alloy exhibits the presence of combine plate, needle and rod-like eutectic silicon phase with very sharp corners and coarser primary silicon particles within the α-Al phase. In addition of 1wt.% of Mn in the eutectic Al-12.6Si alloy, sharp corners of the primary Si and needle-like eutectic Si are became blunt and particles size is reduced. Further, increase in Mn concentration (2.0 wt.%) in the Al-12.6Si alloy, irregular plate shape Al6(Mn,Fe) intermetallics are formed inside the α-Al phase, but the primary and eutectic phase morphology is similar to the eutectic Al-12.6Si alloy. The volume fraction of Al6(Mn,Fe) increases and Al6(Mn,Fe) particles appear as like chain structure in the alloy with 3 wt.% Mn. An increase in Mn concentration in the Al-12.6Si alloys result in the increase in bulk hardness of the alloy as an effects of microstructure modification as well as the presence of harder Al6(Mn,Fe) phase in the developed alloy.

Study of the Boron Distribution and Microstructure of Solidified Al-Si Alloy During the Process of Silicon Purification

AbstractThe Al-Si melts that contain different silicon contents were solidified with a series of cooling rates, and the boron contents in primary silicon phases and eutectic silicon phases were measured and discussed. The results indicate that the boron content in the eutectic silicon phases is higher than that in the primary silicon phases when the cooling rate is constant. When the cooling rate decreases, the boron content in the primary silicon phases decreases, but the boron content in the eutectic silicon phases increases. The microstructure observations of solidified ingots show that there is an interface transition layer beside the primary silicon phase, and the average width of the interface transition layer increases with decreasing cooling rate.

Effect of Sr on the Microstructure of Electromagnetically Stirred Semi-solid Hypoeutectic Al–Si Alloys

The present study investigated the effects of Sr addition on the microstructure of semi-solid Al A356 alloy during electromagnetic stirring. Different amounts of Sr (0–350 ppm) were added to the alloy, and the effect of Sr on eutectic nucleation and growth temperature of the eutectic silicon phase was determined. The results indicate that the addition of the Sr up to 90 ppm increased the solidification range (T L–T S) of the alloy and the further addition of Sr decreased the value of T L–T S. Image analysis revealed that increasing of Sr up to 90 ppm increased the globularity (roundness) of primary aluminum particles. However, the further addition of the Sr reduced the roundness of particles. Also, it was found that the addition of Sr in all amounts increased the area percentage of primary aluminum particles compared to the non-modified alloy. The mechanisms for changes in T L–T S, roundness and area percentage of primary aluminum phase are also discussed.

Microstructure and mechanical properties of Al-7Si-0.7Mg alloy formed with an addition of (Pr+Ce)

Effects of (Pr+Ce) addition on the Al-7Si-0.7Mg alloy were investigated by optical microscope (OM), energy diffraction spectrum (EDS), X-ray diffraction (XRD) and tensile tests. The results showed that the Al-7Si-0.7Mg alloy was modified with (Pr+Ce) addition. The needle-like eutectic silicon phase developed into rose form and the crystalline grains decreased in size and showed a high degree of spheroidization. When the amount of the (Pr+Ce) addition reached 0.6 wt.%, the mean diameter was 31.8 μm (refined by 50%). The aspect ratio decreased to 1.35, and the tensile strength and ductility reached 192.4 MPa and 2.18%, respectively. At higher levels of addition, over-modification occurred, as indicated by increased grain size and reduced mechanical properties. The poisoning effect of the (Pr+Ce) addition on eutectic silicon and the constitutional supercooling caused by the (Pr+Ce) addition were the major causes of alloy modification, grain refinement, and the improvement of mechanical properties.

Deposition and Characterization of Cerium-Based Conversion Coating on HPDC Low Si Content Aluminum Alloy

Cerium-based conversion coatings were deposited on high pressure die cast (HPDC) Al-Si alloys using an immersion method. Hydrogen peroxide and sodium chloride were added to the conversion solution to accelerate the coating formation and to understand its formation mechanism. These studies showed that the deposition of cerium hydroxide/oxide conversion layer starts from iron-rich intermetallic particles, which are located inside the eutectic region and then the coating growth continues to cover the entire alloy surface. This phenomenon passivates the active interfaces between iron-rich intermetallic particles and/or the eutectic silicon phase and the aluminum matrix, which are prone to localized corrosion in chloride ions containing environments. Accordingly, values of the total impedance in EIS measurements significantly increased for the treated substrates. Morphologies of the conversion coatings and the oxidation state of cerium compounds were found to be dependent on the composition of the solution and the presence of chloride ions and/or hydrogen peroxide. Aluminum alloy with higher silicon content showed a more active surface during immersion in the conversion solution. This makes it more difficult to be treated using aggressive conversion solutions.

Effects of zinc coating on interfacial microstructures and mechanical properties of aluminum/steel bimetallic composites

In the present work, the effects of zinc coating on interfacial microstructures and mechanical properties of the aluminum/steel bimetallic composites prepared by a solid-liquid diffusion method were investigated, and the formation mechanism of intermetallic compounds at the interface between the aluminum and the steel were also discussed. The results show that a relatively uniform and compact interface between the aluminum and the steel was formed with the application of the zinc coating. The reaction layer that was mainly composed of τ6-Al4.5FeSi, α-Al rich, α + η eutectoid, η-Zn and eutectic silicon phases, between the aluminum and the steel, had an average thickness of approximately 650 μm. The microhardnesses at the interface between the aluminum and the steel gradually decreased from the steel insert side to the aluminum base side, where the microhardnesses were obviously higher than those of the aluminum base metal. Moreover, the shear stress of the aluminum/steel bimetallic composite with the zinc coating increased by 71% compared to that of the one without the zinc coating. The zinc coating played important roles in the removal of oxidation of the steel insert and the improvement of the wettability between the aluminum and the steel, which promoted the metallurgical reaction of the aluminum with steel, resulting in a significant improvement of the bonding between the aluminum and the steel.

Ultrasonic modification of A356-Al2O3composites

In this work, the dry sliding wear behavior of ultrasonic-modified A356 composite was studied. The main factors in this work are the times and frequencies of ultrasound applied to the composite melt, which were in the range of 5–15 min and 10–50 Hz, respectively. It is indicated that there is an effective range of time and frequency within which decreasing the grain size and also uniformity in the distribution of the eutectic silicon phase, Al2 O3 reinforcement particles and solidification shrinkage pores can be achieved. Frequencies up to 50 Hz during a time longer than 10–15 min yielded the proper conditions in this case. With these conditions of structural modification, an optimum decrease in the grain size with less directionality of the columnar or dendritic grains is seen. A decrease in the grain size and more uniformity in the microstructure gives rise to decreases in the wear rate at a given load. At higher loads, the oxide debris is expected to become better compacted to form a transfer layer, spread over a larger area of the sliding surface, and thus its removal causes greater wear compared with that without removal of wear debris. The results indicate that the frequency is more effective in the reduction procedure of the grain size and density than the time.

Microstructure and phase formation in Al–20Si–5Fe–3Cu–1Mg synthesized by selective laser melting

The Al–20Si–5Fe–3Cu–1Mg alloy was fabricated using selective laser melting (SLM). The microstructure and the phase constitution of the SLM as well as the heat treated alloy were studied. It is found that SLM not only alters the morphology of the eutectic silicon phase from rod-like to dendrite as well as particle shapes, but also significantly refines the primary silicon and Al–Si–Fe compound compared with the corresponding cast alloy. The eutectic silicon becomes coarser, whereas the primary silicon phase, the Al–Si–Fe compound show little change after heat treatment. X-ray diffraction results show the presence of only δ-Al4FeSi2 phase in the SLM alloy, whereas, the heat treated SLM alloy consists of both δ-Al4FeSi2 and β-Al5FeSi phases. The DSC analysis reveals that no quasi-peritectic reaction occurs during cooling cycle on account of the high cooling rate as well as the large diffusion distances required by the large dimensions of the δ-Al4FeSi2 phase.

Enhancement in tribological behaviour of functionally graded SiC reinforced aluminium composites by centrifugal casting

Enhanced tribological and location-specific properties achieved in functionally graded metallic composites make them potential materials for futuristic engineering components. The present investigation aims on the processing of homogenous and functionally graded Al matrix composites reinforced with SiC particles of 23 µm average particle size by gravity and centrifugal casting techniques. The sizes of the primary aluminium and eutectic silicon phases are finer towards the outer periphery due to the higher solidification rate. Functionally graded Al–SiCp composite rings produced by centrifugal casting show higher concentration of SiCp towards outer periphery, followed by a gradient transition region and the particle depleted zone. Particle agglomerates formed due to partially wetted particles associated with voids and gas porosities segregate towards the inner periphery. The higher concentration of reinforcement particles near the outer periphery in FGM enhances the hardness and wear resistance in rotary and reciprocating wear studies. Centrifugal cast alloys show enhanced wear resistance than the gravity cast specimen due to fine grains of primary aluminium and eutectic silicon. The rotary and reciprocating wear test shows the adhesive and abrasive type wear mechanisms.

Modification of Hypereutectic Al-20%Si Alloy by Neodymium

The modification mechanism was studied by OM, SEM, XRD and Trace Element Analysis. The results of OM and SEM analysis show that pure Nd can effectively refine primary and eutectic silicon in hypereutectic Al-20%Si alloy. Morphology of primary silicon is transformed from pentalpha to block and the average grain size of primary silicon is reduced from 80~120μm to 20~50μm after modification. Trace Element Analysis results show that Nd can purity base metal and reduce impurity contents. XRD patterns show that no new phase formed after Nd modification. The results of mechanical properties test show that whole properties of modified sample are significantly improved. Tensile strength increases about 35.8% from 117 MPa to 148 MPa after modification, Elongation change increases about 193% from 0.56% to 1.64%. The improvement of mechanical properties should be attributed to fine primary Si phase and eutectic silicon phase and purification of base metal after modification.

Influence of Neodymium on Wear Resistance of Hypereutectic Al-Si Alloy

The morphology of eutectic and primary silicon phases was analyzed by OM and SEM. OM and SEM results show that pure Nd can significantly refine both eutectic and primary silicon of hypereutectic Al-20%Si alloy. Morphology of primary silicon is transformed from star-shaped and irregular morphology to fine polyhedral and grain size of primary silicon is refined from 80~120 μm to 20~50 μm. Friction and wear resistance tests show that friction coefficient of Al-20%Si alloy reduces after Nd modification. Wear resistance of Al-20%Si alloy after modification is significantly improved as compared to the initial sample. The dominant wear mechanism for 0.3% Nd modified alloy is abrasive wear, adhesive wear and oxidative wear mechanism, but wear mechanism for unmodified alloy is abrasive wear and adhesive wear mechanism.

Combined effects of mechanical vibration and wall thickness on microstructure and mechanical properties of A356 aluminum alloy produced by expendable pattern shell casting

Abstract In the present work, the combined effects of mechanical vibration and wall thickness on the microstructure and mechanical properties of A356 aluminum alloy produced by the expendable pattern shell casting process were investigated. It has been found that with the increase of wall thickness, the morphologies of the α-Al primary phase and eutectic silicon phase of the samples obtained from the conventionally cast evolved from a fine dendrite to a coarse dendrite and from a fibrous structure to a plate-like structure, respectively, and the mechanical properties of A356 aluminum alloy decreased continuously. After the mechanical vibration was applied, the coarser dendrites transformed into the fine equiaxed grains, and the size, morphology and distribution of the α-Al primary phase and eutectic silicon particles as well as SDAS were improved significantly. Meanwhile, the mechanical properties and density of A356 aluminum alloy increased greatly, and the tensile strength, yield strength, elongation as well as hardness of the sample with 40 mm wall thickness were 35%, 42%, 63% and 29% higher than that of the conventionally cast under the T6 condition, respectively. The effect degree of the mechanical vibration on the microstructure and mechanical properties increased with increasing wall thickness. Furthermore, the mechanical vibration changed the fracture mode of A356 aluminum alloy from a transgranular fracture mode of the conventionally cast to an intergranular fracture mode.

Automotive copper and magnesium containing cast aluminium alloys: Report on the correlation between Yttrium modified microstructure and mechanical properties

An experimental investigation is carried out in order to measure and thus report the effect of SDAS values on the mechanical properties of the Yttrium modified casting Al alloys. Microstructural features and the alloy composition determine the mechanical properties of the as-cast Al alloys. The solidification rate plays the main role on the microstructural characteristics including primary and secondary dendrites arm spacing (DAS and SDAS), also the fraction, size and distribution of defects, eutectic silicon and intermetallic phases. In this study, Yttrium is used as a chemical modifier to the cast Al alloys in an attempt to transform the acicular shape of the Si to the fibrous morphology. The investigation of the samples show the presence of the pores and voids in the microstructure of the as-cast Y modified alloy. The typical cast microstructure shows dendritic Al accompanied with eutectic Si and Al2Cu, Al15(Fe, Mn)3Si2 and other complex multi-element intermetallic. Based on the findings of the tensile tests, strength of the Y modified alloy declines with increasing the SDAS values.

Influence of Si Content on Microstructure and Erosion Properties of Al-Based Alloy

In order to develop new protective materials for magnesium alloy, Al-based alloys with different Si-content were fabricated by copper mold casting. Microstructure, erosion properties of the ingot samples were characterized or tested by using spectrum analysis, optical imcroscope, salt testing machine etc, respectively. The results indicated that the microstructure of Al-1.9Si-1.32Mg-0.40Mn was mostly dendritic crystal. That of Al-13Si consisted of α-Al, flaky eutectic silicon and primary crystal silicon. That of Al-18Si-0.01%P was consistent of a large proporation of primary crystal silicon phase, a part of eutectic silicon phase and a little of α-Al phase. With Si-content increasing, anti-corrosion properties of Al-based alloy gradually improved, which could provide theoretical principle to determine chemical elements of protective materials for magnesium alloy.

Analysis of the Antimony and Strontium Cross-Effects in Al-Si Foundry Alloys

In this work we show the effect of various concentrations of strontium and antimony on the level of modification in the Al-Si alloy. The scale of the modification rate was determined in two ways: thermal analysis was performed and the images of the samples. The eutectic temperature registered during the analysis were compared to the eutectic temperature of the unmodified alloy and on the basis of them was determined which samples are registered as modified, which are not. On the basis of the results of the cooling curves the partially modified category was introduced, if the ΔT value is less than 9°C and more than 7.5°C. The samples made of the alloys were examined with a computer image analysis and the samples were grouped on the basis of the size of the eutectic silicon phases. The aim of our research work was the examination of cross-effects of strontium and antimony.

The Effects of Electric Pulse Modification on Eutectic Al-12.6%Si alloy

Al-Si alloy at eutectic region as the research object, Electric pulse modification (EPM) were used to achieve simultaneous refinement and modification of eutectic silicon phase, in order to analyze the mechanism of electrical pulse modification to the alloy and analyzed how the EPM affects the solidification structure and the corresponding properties. We get the conclusion by observing the microstructure of the sample, measuring the hardness, calculating the volume fraction and the average size of primary silicon at different pulse frequency and voltage. By using this process the particle size of primary silicon was reduced from 50 µm to a range of 5-20µm and the shape changes from acicular to fine fiber when compared with the conventional casting process. Also, the result of mechanical test showed that the hardness increase from 105HV-156HV with the change in pulse voltage at 700V peak value it therefore increased with 49% and at 1000V decline to 144HV with increased by 37% with homogeneous distribution of eutectic silicon.

Effect of Elements Cerium and Lanthanum on Eutectic Solidification of Al-Si-Cu near Eutectic Cast Alloy

The properties of Al-Si-Cu cast alloys are strongly affected by eutectic Al-Si and Al-Cu phases. The characteristic parameters of these two phases with additions cerium 1wt % (Ce) and lanthanum1 wt % (La) were investigated in Al-11Si-2Cu near eutectic alloy using computer-aided cooling curve thermal analysis. As a result, the La additive showed the highest (TNAl-Si) while the Ce additive showed very little effect. In addition, the growth temperature (TGAl-Si) is decreased by adding Ce compared to the base alloy and La addition. Additives showed an increase of recalescence magnitude (TRAl-Si). Addition La and Ce increased the nucleation and growth temperature of Al-Cu phase. The microstructure analysis on the silicon morphology showed that 1 wt % La and 1 wt % Ce additions play refiner role in Al-Si-Cu near eutectic alloys. Findings are also confirmed by aspect ratio of eutectic silicon phase.

The Changes of Fatigue Properties in Aluminium Cast Alloy during Solution Treatment

This paper describes the effect of solution treatment on the fatigue properties of AlSi9Cu3 cast alloy. The heat treatment consisted of a solution treatment at two different temperatures 515°C and 525°C, a holding time of 4 hours; water quenching at 40°C and natural aging at room temperature for 24 hours. Thus prepared samples were subjected to fatigue test with a rotating bending loading (testing machine ROTOFLEX operating at 30 Hz, load ratio R = -1). The fatigue fracture surfaces were observed using a scanning electron microscope (SEM) after the fatigue test. The results showed that the existence of casting defects (8.4 % of micro-shrinkage) has considerable influence on fatigue properties and can be considered as fatigue crack initiators in what leads to final fatigue damage. Apart from cast defects, the morphology of eutectic silicon and intermetallic phases (Fe- and Cu-rich phases) are also important factors which have an influence on the fatigue properties of Al-Si cast components. The solution treatment used (at 525°C/4hours) has increased fatigue properties (the fatigue lifetime increased from 49 to 76 MPa), thanks to Si particles, morphology changes, and cast defects area reduction as well as reduction Fe-rich phases.