Effect of slow shot speed on externally solidified crystal,porosity and tensile property in a newly developed high-pressure die-cast Al-Si alloy

The effect of slow shot speed on externally solidified crystal(ESC),porosity and tensile property in a newly developed high-pressure die-cast Al-Si alloy was investigated by optical microscopy(OM),scanning electron microscopy(SEM)and laboratory computed tomography(CT).Results showed that the newly developed AlSi9MnMoV alloy exhibited improved mechanical properties when compared to the AlSi10MnMg alloy.The AlSi9MnMoV alloy,which was designed with trace multicomponent additions,displays a notable grain refining effect in comparison to the AlSi10MnMg alloy.Refining elements Ti,Zr,V,Nb,B promote heterogeneous nucleation and reduce the grain size of primaryα-Al.At a lower slow shot speed,the large ESCs are easier to form and gather,developing into the dendrite net and net-shrinkage.With an increase in slow shot speed,the size and number of ESCs and porosities significantly reduce.In addition,the distribution of ESCs is more dispersed and the net-shrinkage disappears.The tensile property is greatly improved by adopting a higher slow shot speed.The ultimate tensile strength is enhanced from 260.31 MPa to 290.31 MPa(increased by 11.52%),and the elongation is enhanced from 3.72%to 6.34%(increased by 70.52%).

Effect of erbium on properties and microstructure of Al-Si eutectic alloy

Eutectic Al-12.6 wt.%Si alloys with various contents of the rare earth element Er were prepared by the conventional casting technique. The effect of Er on the microstructure and properties of the eutectic Al-Si alloys was investigated using optical microscopy, scanning electron microscopy as well as the friction and wear tests. It was found that the addition of Er obviously improved the anti-wear properties, and reduced the friction coefficient of the alloys. The appropriate addition of Er would change the size and shape of the eutectic silicon, and thereby refine the microstructure of the Al-Si alloys. The refinement mechanism was also discussed.

Microstructure and mechanical properties of hypereutectic Al-Si alloy modified with Cu-P

The microstructure and mechanical properties of Al-14.6Si castings modified by Cu-P master alloy under different conditions were studied with optical microscope（OM） and mechanical testing and simulation（MTS）.The results indicate that the Cu-P master alloy possesses not only obvious modification effect,but also longevity effect with more than 8 h on the hypereutectic Al-Si alloy.It is shown from thermal calculation,scanning electron microscope（SEM）,and energy dispersive analysis of X-rays（EDAX） that the modification mechanism of Cu-P on primary silicon in the castings is heterogeneous nucleation around AlP particles.The Cu-P master alloy has no or little modifying effect on eutectic silicon,even though it has obvious modification on primary silicon in the castings.This may be because of the fast transformation of eutectic silicon at a very narrow temperature,which will notably weaken the role of AlP particles as heterogeneous nuclei for eutectic silicon.

Effect of addition of Al-Si eutectic alloy on microstructure and mechanical properties of Mg-12wt%Li alloy

Mg-12 Li, Mg-12 Li-3（Al-Si）, Mg-12 Li-7（Al-Si） and Mg-12 Li-9（Al-Si） alloys（all in wt%） were fabricated by high frequency vacuum induction melting in a water cooled copper crucible. After subsequently hotrolling and annealing, their microstructure and mechanical properties were investigated. Experimental results show that mechanical properties of Mg-12 Li alloy were significantly improved by the addition of Al-Si eutectic alloy. Mg-12 Li-7（Al-Si） alloy shows the highest strength of 196 MPa of the investigated alloys, which is about 1.8 times of the strength of Mg-12 Li alloy, and maintains high elongation of 27%.The improved mechanical property with addition of Al and Si in the eutectic proportion into Mg-12 Li alloy was attributed to the solution strengthening effect of A1 and precipitation hardening effect from AlLi and Mg_2 Si precipitates.

Functions and mechanism of modification elements in eutectic solidification of Al-Si alloys:A brief review

Being used more and more widely in engineering,AlSi alloys comprise about 80%of all kinds of aluminum alloys,which are the most widely utilized nonferrous alloys.Although most Al-Si alloys consist of multiple components,the eutectics in the structure accounts for 50%-90%of the sum volume of such alloys.Therefore,understanding the modification mechanism and function rules of the AlSi eutectic solidification is the technical key in controlling the structures and properties of such casting alloys.The present paper chiefly reviews recent investigation developments and important conclusions along the lines of the functions of modification elements and their modification mechanism in the eutectic solidification of Al-Si alloys.

Solidification structure of eutectic Al-Si alloy under a high magnetic field-aid-electromagnetic vibration

An electromagnetic vibration was generated by simultaneously imposing a strong static magnetic field （up to 10 T） and an alternative electricity current to the metal. Its effects on the solidification structure of eutectic Al-Si alloy have been investigated experimentally. It is found that the eutectic structure has been refined by solely imposing high magnetic field while it is coarsened under the electromagnetic vibration. Furthermore, polyhedral Si grains and non-dendritic α-Al appeared when the electromagnetic vibration strength was strong enough. The refining of eutectic structure is attributed to the decrease of diffusion coefficient caused by the strong magnetic field. The coarseness of eutectic structure may be attributed to the convection caused by electromagnetic vibration. Strong convection may break co-operative growth of eutectic phases to form polyhedral Si grains and non-dendritic α-Al.

Research on semi-solid slurry of a hypoeutectic Al-Si alloy prepared by low superheat pouring and weak electromagnetic stirring

The semi-solid slurry of a hypoeutectic Al-Si alloy was manufactured by low superheat pouring and weak electromagnetic stirring. The effects of pouting temperature and stirring power on the semi-solid slurry were investigated. The results indicated that the semi-solid slurry to satisfy rheocasting can be manufactured by low superheat pouring and weak electromagnetic stirring. The pouring temperature （or superheat） and the stirring power remarkably affected the morphology of primary α-Al and the size of primary α-Al, and there is no obvious effect of stirring time on primary α-Al. Compared with the samples made by low superheat pouring with no stirring, the nucleation rate, particle morphology and grain size of primary α-Al in A356 were markedly improved by low superheat pouring and weak electromagnetic stirring. On the condition of weak electromagnetic stirring, the pouring temperature with low superheat can be suitably raised to reach the effectiveness obtained from the lower pouring temperature without stirring.

Manufacture technique of semi-solid slurry of hypoeutectic Al-Si alloy by low superheat pouring and weak electromagnetic stirring

The semi-solid slurry of hypoeutectic Al-Si alloy was manufactured by low superheat pouring and weak electromagnetic stirring. The effects of pouring temperature and stirring power on the semi-solid slurry making process were investigated. The results indicate that the semi-solid slurry to satisfy rheocasting requirement can be made by a combination of low superheat pouring and weak electromagnetic stirring. The pouring temperature (or superheat) and the stirring power significantly affect the morphology and the size of primary α-Al, while there is no obvious effect of the stirring time on primary α-Al. Compared with the samples made by low superheat pouring without stirring, the nucleation rate, particle morphology and grain size of primary α-Al in A356 Al alloy are markedly improved by a process of applying both low superheat pouring and weak electromagnetic stirring. Under the condition of weak electromagnetic stirring applied, the pouring temperature with low superheat can be equivalently to reach the effectiveness obtained from the even lower pouring temperature without stirring.

Formation of hypereutectic silicon particles in hypoeutectic Al-Si alloys under the influence of high-intensity ultrasonic vibration

The modification of eutectic silicon is of general interest since fine eutectic silicon along with fine primary aluminum grains improves mechanical properties and ductilities. In this study, high intensity ultrasonic vibration was used to modify the complex microstructure of aluminum hypoeutectic alloys. The ultrasonic vibrator was placed at the bottom of a copper mold with molten aluminum. Hypoeutectic Al-Si alloy specimens with a unique in-depth profile of microstructure distribution were obtained. Polyhedral silicon particles, which should form in a hypereutectic alloy, were obtained in a hypoeutectic Al-Si alloy near the ultrasonic radiator where the silicon concentration was higher than the eutectic composition. The formation of hypereutectic silicon near the radiator surface indicates that high-intensity ultrasonic vibration can be used to influence the phase transformation process of metals and alloys. The size and morphology of both the silicon phase and the aluminum phase varies with increasing distance from the ultrasonic probe/radiator. Silicon morphology develops into three zones. Polyhedral primary silicon particles present in zoneⅠ, within 15 mm from the ultrasonic probe/radiator. Transition from hypereutectic silicon to eutectic silicon occurs in zoneⅡ about 15 to 20 μm from the ultrasonic probe/radiator. The bulk of the ingot is in zoneⅢ and is hypoeutectic Al-Si alloy containing fine lamellar and fibrous eutectic silicon. The grain size is about 15 to 25 μm in zoneⅠ, 25 to 35 μm in zoneⅡ, and 25 to 55 μm in zoneⅢ. The morphology of the primary α-Al phase is also changed from dendritic (in untreated samples) to globular. Phase evolution during the solidification process of the alloy subjected to ultrasonic vibration is described.

Distributions of Sr and Fe and their influence on modification of hypoeutectic Al-Si alloy

The influence of cooling rate and Fe-containing phases on Sr-modification of Si phases in hypoeutectic Al-Si alloys, a problem with great industrial importance, was investigated. The microstructures of samples were examined using scanning electron microscopy(SEM) with energy-dispersive X-ray spectroscopy(EDX). A new method of electron probe microanalysis(EPMA) map scanning was used to analyze the Sr distribution, which gave quantitative results covering more Si particles. EPMA map scanning, together with SEM with EDX, was also used in analyzing the distribution of Fe phases. Results show that Fe-containing phase was related to the unmodified Si particles in samples with partial modification failure and the plate-like Si phases in samples without modification failure. Such a relationship was further confirmed by the microstructure observation.In conclusion, a partial failure of Sr-modification can be caused by both slow cooling rate and Fe-containing phases.

Microstructure and Mechanical Properties of Hyper-eutectic Al-Si Alloys Fabricated by Spray Casting

Microstructure and mechanical properties of hyper-eutectic Al-Si alloy fabricated by spray casting were in- vestigated and then these results were compared with those by squeeze cast.The spray-cast specimen was found to have finer Si particles （～5μm） compared to the squeeze-cast specimen （10-25μm）.The tensile strength and elongation of the spray-cast specimen are also higher than those of the squeeze cast one.It was considered that the increased mechanical properties of the spray-cast specimen were mainly due to finer size of the Si particles distributed in Al matrix.

Effects of P+Cr complex modification and solidification conditions on microstmcture of hypereutectic Al-Si alloys by wedge-shaped copper mould casting

Large and segregated primary Si particles may drastically decrease the mechanical properties of Al-Si alloys. To solve this problem, a P-Cr complex modif ier was added into the alloy, and the effects of P-Cr complex modification and solidification conditions on the microstructure of hypereutectic Al-Si alloys casting produced in wedge-shaped copper mould were studied. The thermal analysis technique was applied to calculate the cooling rate during solidification. The microstructures were observed by means of optical and scanning electron microscopies. Results showed that the primary Si segregates in the as-cast hypereutectic Al-Si alloys. The segregation of primary Si can be inhibited by adding a P+Cr complex modif ier and increasing the cooling rate during solidif ication. The ref inement of primary Si particles by P+Cr complex modif ication is due to the formation of CrS i2 and AlP particles which act as the heterogeneous nuclei for the primary Si phase. The segregation of Si was also inhibited through the adherence of heavier CrS i2 particles to the primary Si particles.

Characteristics and Microstructure of a Hypereutectic Al-Si Alloy Powder by Ultrasonic Gas Atomization Process

A hypereutectic Al-Si alloy powder was prepared by ultrasonic gas atomization process. The morphologies, microstructure and phase constituent of the alloy powder were studied. The results showed that powder of the alloy was very fine and its microstructure was mainly consisted of Si crystals plus intermetallic compound A19FeSi3, which were.very fine and uniformly distributed.

Effect of heat treatment on eutectic silicon morphology and mechanical property of Al-Si-Cu-Mg cast alloys

Through morphology observation on silicon particles of Al-Si-Cu-Mg cast alloy, it is found that during solution treatment the evolution of eutectic silicon morphology and their effect on mechanical properties can be classified into three stages. In the initial stage, necking, stubbing and fragmentation of silicon particles result in the improvement of plasticity of alloy. In the intermediate stage, the mechanical properties of 354 alloy attain peak values due to spheroidization of silicon particles. In the final stage, the drop of hardness and strength is related to the deterioration of silicon morphology. The facets and lap occur in silicon particles and the coarsening process of silicon follows LSW model. During aging, the clusters of excess silicon can work as barriers for dislocation movement and thus enhance the strength of alloy. On the other hand, excess Si affects the process of aging precipitation and leads to a fine and highly dense distribution of GP zones, finally effectively strengthens the alloy.

Refining Effect of Boron on Hypoeutectic Al-Si Alloys

Several concepts of the grain refinement mechanism of B on hypoeutectic Al-Si alloys have been adopted: the refining effect of B on the a-AI and eutectic Si with the different additions of Al-B master alloys made at 850℃ was investigated; and the Al-B master alloys formed under different temperature conditions have been studied to explore the morphologies of AIB2 particles; slowly cooled sample with addition of Al-B was made to explore the refinement mechanism. AI-B master alloy can refine not only a-AI, but eutectic Si. Theoretical analysis indicates that, although AIB2 does not take part directly in the nucleation process in pure Al in the presence of Si, it provides a substrate for precipitation of a small content of Si from which a-At will grow without any undercooling. When the temperature decreases to eutectic line, AIB2 subsequently nucleates eutectic Si; AIB2 particles appear in two different morphologies, namely, hexagonal platelet and tetradehedron morphology which depend on the processing temperature conditions.

Investigation on corrosion behaviour of asextruded near eutectic Al-Si-Mg alloy by neutral salt spray test

In order to provide scientific basis for advanced applications of near eutectic Al-Si-Mg alloys as architectural prof iles,a comparative study on the corrosion resistance of an as-extruded near eutectic Al-Si-Mg alloy and AA6063 aluminium alloy was carried out by means of neutral salt spray test.The corroded surfaces of the alloys were examined with optical microscopy and scanning electron microscope(SEM).Results show that the corrosion type of these two alloys is pitting corrosion.The number of corrosion pits in the AA6063 aluminium alloy is more than that in the near eutectic Al-Si-Mg alloy,but the pits in the latter alloy are much larger and deeper.Because the relatively low polarization resistance of the near eutectic alloy leads to poorer repassivation ability,autocatalytic acidif ication occurs once a pit forms.Thus,occluded corrosion cells are developed in this alloy.

Effect of AlP master alloy on grain refinement of primary silicon in eutectic Al-Si alloys

To obtain the finer primary silicon crystals, the proprietary Al-P masteralloy was adopted to modify the eutectic Al-Si alloys and the most suitable modification process wasmade in the experiments. The SEM (Scanning Electron Microscope) and DSC (Differential ScanningCalorimeter) analysis indicate that the Al-P modifier has more advantages over Cu-P and Fe-Pmodifier in easily addition, no elemental alteration and less undercooling of primary silicon'ssolidification, which suggests the Al-P master alloy is an effective modifier of eutectic Al-Sialloys.

Influence of titanium content on wear resistance of electrolytic low-titanium eutectic Al-Si piston alloys

The wear resistance of six kinds of the electrolytic low-titanium eutectic Al-Si piston alloys with various Ti content ranging from 0.00wt.% to 0.21wt.% has been studied. A new method of adding Ti is adopted in the electrolytic low-titanium aluminum alloy ingots. The electrolytic low-titanium eutectic Al-Si piston alloys are produced by remelting the electrolytic low-titanium aluminum alloy, crystal silicon, pure magnesium, Al-50%Cu and Al-10%Mn master alloy. The wear experiments are conducted using MM200 wear testing machine under lubricating condition. The results indicate that the better wear resistance and the less weight loss are achieved in the study for the eutectic Al-Si piston alloys with 0.08wt.%–0.12wt.% Ti content. The highest ultimate tensile strength of 135.94 MPa at 300℃ and HV141.70 hardness of the alloys are obtained at 0.12wt.% and 0.08wt.% Ti content, respectively. The wear mechanism of the eutectic Al-Si piston alloys under lubricating condition is abrasive wear.

Effect of A1P master alloy on grain refinement of primary silicon in eutectic Al-Si alloys

To obtain the finer primary silicon crystals, the proprietary Al-P master alloy was adopted to modify the eutectic Al-Si alloys and the most suitable modification process was made in the experiments. The SEM (Scanning Electron Microscope) and DSC (Differential Scanning Calorimeter) analysis indicate that the Al-P modifier has more advantages over Cu-P and Fe-P modifier in easily addition, no elemental alteration and less undercooling of primary silicon’s solidification, which suggests the Al-P master alloy is an effective modifier of eutectic Al-Si alloys.

Effects of Si Content and the Addition Amount of Al-3B Master Alloy on the Solidification Structures of Hypoeutectic Al-Si Alloys

Effects of Si content and the addition amount of Al-3B master alloy on the solidification structures of hypoeutectic Al-Si alloys were studied. The addition amounts of the master alloy were 0.2%, 0.4%, 0.7% and 1% (mass fraction, so as the follows), respectively. The Si content of Al-Si binary alloys investigated varied from 1% to 11%. The observation of macrostructures of non-refined samples showed that 3% Si constitutes a transition point at which the minimum grain size can be obtained. It was also found that Al-3B master alloy can shift the transition point towards a higher Si value when its addition amount increases, making this point appear at 4%, 5% and 6% Si as its addition amount increases up to 0.4%, 0.7% and 1%, respectively.