Effect of ultrasonic vibration on Fe-containing intermetallic compounds of hypereutectic Al-Si alloys with high Fe content

The Fe-containing intermetallic compounds with high melting point in hypereutectic Al-Si alloys can improve the heat resistance and wear resistance at elevated temperatures. However, the long needle-like Fe-containing compounds in the alloys produced by conventional casting process are detrimental to the strength of matrix. The effect of ultrasonic vibration （USV） on the morphology change of Fe-containing intermetallic compounds in the hypereutectic Al-17Si-xFe （x=2, 3, 4, 5） alloys was systematically studied. The results show that, the Fe-containing intermetallic compounds are mainly composed of long needle-like β-Al5FeSi phase with a small amount of plate-like δ-Al4FeSi2 phase in Al-17Si-2Fe alloy produced by conventional casting process. With the increase of Fe content from 2% to 5% in the alloys, the amount of plate-like or coarse needle-like δ-Al4FeSi2 phase increases while the amount of long needle-like β-Al5FeSi phases decreases. In Al-17Si-5Fe alloy, the Fe-containing intermetallic compounds exist mainly as coarse needle-like δ-Al4FeSi2 phase. After USV treatment, the Fe-containing compounds in the Al-17Si-xFe alloys are refined and exist mainly as δ-Al4FeSi2 particles, with average grain size ranging from 26 μm to 37 μm, and only a small amount of β-Al5FeSi phases remain. The mechanism of USV on the morphology of Fe-containing intermetallic compounds was also discussed.

Dry sliding wear behavior of rheocast hypereutectic Al-Si alloys with different Fe contents

The effect of iron content on wear behavior of hypereutectic Al?17Si?2Cu?1Ni alloy produced by rheocasting process was investigated. The dry sliding wear tests were carried out with a pin-on-disk wear tester. The results show that the wear rate of the rheocast alloy is lower than that of the alloy produced by conventional casting process under the same applied load. The fine particle-likeδ-Al4(Fe,Mn)Si2 and polygonalα-Al15(Fe,Mn)3Si2 phases help to improve the wear resistance of rheocast alloys. As the volume fraction of fine Fe-bearing compounds increases, the wear rate of the rheocast alloy decreases. Moreover, the wear rate of rheocast alloy increases with the increase of applied load from 50 to 200 N. For the rheocast alloy with 3% Fe, oxidation wear is the main mechanism at low applied load (50 N). At higher applied loads, a combination of delamination and oxidation wear is the dominant wear mechanism.

Effects of Mg content on primary Mg_2Si phase in hypereutectic Al-Si alloys

Hypereutectic Al-Si alloy with variant Mg contents were fabricated by casting,and the effects of Mg content on the microstructure of primary Mg2Si particles in hypereutectic Al-Si alloys were investigated.The results show that the volume fraction of primary Mg2Si particles increases linearly with raising the Mg content,but the average size of Mg2Si particles does not exhibit a corresponding change.When the Mg content is 3%,á1 0 0？ directions have the fastest growth velocity,so that Mg2Si particles are likely to form octahedron shape.When gradually increasing the Mg content,the distributions of Mg and Si atoms on the solid-liquid interface become inhomogeneous,which results in the formation of irregular octahedron structures.Finally,when the Mg content is about 10%,the morphology of primary Mg2Si particles changes from the octahedron shape into various complex structures with a large size.

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.

Influence of high pressure and manganese addition on Fe-rich phases and mechanical properties of hypereutectic Al-Si alloy with rheo-squeeze casting

The influence of high pressure and manganese addition on Fe-rich phases(FRPs)and mechanical properties of Al-14Si-2Fe alloy with rheo-squeeze casting(RSC)was investigated.The semi-solid alloy melt was treated by ultrasonic vibration(UV)firstly,and then formed by squeeze casting(SC).Results show that the FRPs in as-cast SC alloys are composed of coarseβ-Al5(Fe,Mn)Si,δ-Al4(Fe,Mn)Si2 and bone-shapedα-Al15(Fe,Mn)3Si2 phases when the pressure is 0 MPa.With RSC process,the FRPs are first refined by UV,and then the solidification under pressure further causes the grains to become smaller.The peritectic transformation occurs during the formation ofαphase.For the alloy with the same composition,the ultimate tensile strength(UTS)of RSC sample is higher than that of the SC sample.With the same forming process,the UTS of Al-14Si-2Fe-0.8Mn alloy is higher than that of Al-14Si-2Fe-0.4Mn alloy.

Effect of hot extrusion process on microstructure and mechanical properties of hypereutectic Al-Si alloys

The hypereutectic Al-Si alloy was fabricated by hot extrusion process after solidified under electromagnetic stirring,and the microstructure and mechanical properties of the alloy were studied.The results show that the ultimate tensile strength and elongation of the alloy reached 229.5 MPa and 4.6%,respectively with the extrusion ratio of 10,and 263.2 MPa and 5.4%,respectively with extrusion ratio of 20.This indicates that the mechanical properties of the alloy are obviously improved with the increase of extrusion ratio.After hot extruded,the primary Si,eutectic Si,Mg2Si,AlNi,Al7Cu4Ni and Al-Si-Mn-Fe-Cr-Mo phases are refined to different extent,and the efficiency of refinement is obvious more and more with the increase of extrusion ratio.After T6 heat treatment,the sharp corners of these phases become passivated and roundish,and the mechanical properties are improved.The ultimate tensile strength of the extruded alloy after T6 heat treatment reaches 335.3 MPa with extrusion ratio of 10 and 353.6 MPa with extrusion ratio of 20.

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 AI-Si alloys. To solve this problem, a P-Cr complex modifier 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 AI-Si alloys. The segregation of primary Si can be inhibited by adding a P＋Cr complex modifier and increasing the cooling rate during solidification. The refinement of primary Si particles by P＋Cr complex modification is due to the formation of CrSi2 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 CrSi2 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.

Effects of ZnS modification on primary Si in hypereutectic Al-Si alloy

A new modifying agent, ZnS, was used as a refiner to modify primary silicon in hypereutectic AlSi alloy. The factors affecting the modification results, including addition level of ZnS and holding time, were investigated. The results showed that the average size of the most effectively modified primary silicon was 28.5 μm when the ZnS mixed powder addition was 0.15 wt.% with a holding time of 10 min. More important, the average size of primary silicon could remain below 40 μm despite the holding time extending to 120 min, which means ZnS is a promising modifying agent of primarySi in industrial applications.

Hypereutectic Al-Si Matrix Composites Prepared by In Situ Fe_(2)O_(3)/Al System

Al_(2)O_(3) particles reinforced hypereutectic Al-Si composites were prepared by in situ Fe_(2)O_(3)/Al reaction system.The thermodynamic analysis and microstructure evolution were investigated by differential scanning calorimetry,optical microscope,scanning electronic microscopy and transmission electron microscope.Results show that the reaction between Fe_(2)O_(3) and Al is spontaneous which can be separated into two steps at different temperatures.The in situ Al_(2)O_(3) particles in nano size distribute on the Al matrix accompanied with long needle-shapedβFe-rich intermetallic phase.With different content of Mn addition,βphase can be modified toα-Al15(Mn,Fe)3Si2 andδ-Al4(Fe,Mn)Si2.Both tensile strength and elongation results at room temperature and 300℃reveal that the optimal Fe-rich intermetallic phase is finer Chinese-script and polyhedralαphase with a Mn/Fe mass ratio 0.5 for the composites.Both in situ Al_(2)O_(3) particles andα-Fe phases contribute to the properties improvement of the composites。

Microstructure evolution and phase transformation of traditional cast and spray-formed hypereutectic aluminium-silicon alloys induced by heat treatment

Microstructural evolution and phase transformation induced by different heat treatments of the hypereutectic aluminium-silicon alloy, Al-25Si-5Fe-3Cu （wt%, signed as 3C）, fabricated by traditional cast （TC） and spray forming （SF） processes, were investigated by differential scanning calorimetry （DSC） and scanning electron microscopy （SEM） combined with energy dispersive X-ray spectroscopy and X-ray diffraction techniques. The results show that A17Cu2Fe phase can be formed and transformed in TC- and SF-3C alloys between 802-813 K and 800-815 K, respectively. The transformation from β-Al5FeSi to δ-Al4FeSi2 phase via peritectic reaction can occur at around 858-870 K and 876-890 K in TC- and SF-3C alloys, respectively. The starting precipitation temperature of δ-Al4FeSi2 phase as the dominant Fe-bearing phase in the TC-3C alloy is 997 K and the exothermic peak about the peritectic transformation of δ-Al4FeSi2→β-Al5FeSi is not detected in the present DSC experiments. Also, the mechanisms of the microstructural evolution and phase transformation are discussed.

Influence of rheo-diecasting processing parameters on microstructure and mechanical properties of hypereutectic Al-30%Si alloy

The effects of pouring temperature,vibration frequency,and the number of curves in a serpentine channel,on themicrostructure and mechanical properties of Al-30%Si alloy processed by rheo-diecasting(RDC)were investigated.The semisolidAl-30%Si alloy slurry was prepared by vibration serpentine channel pouring(VSCP)process in the RDC process.The results showthat the pouring temperature,the vibration frequency,and the number of the curves strongly affect the microstructure and mechanicalproperties of Al-30%Si alloy.Under experimental conditions of a pouring temperature of850°C,a twelve-curve copper channel anda vibration frequency of80Hz,the primary Si grains are refined into fine compact grains with average grain size of about24.6μm inthe RDC samples assisted with VSCP.Moreover,the ultimate tensile strength(UTS),elongation and hardness of the RDC sample are296MPa,0.87%and HB155,respectively.It is concluded that the VSCP process can effectively refine the primary Si grains.Therefinement of primary Si grains is the major cause for the improvement of the mechanical properties of the RDC sample.

Effect of mixing rate and temperature on primary Si phase of hypereutectic Al-20Si alloy during control ed diffusion solidification(CDS) process

Controlled Diffusion Solidification(CDS) is a promising process relied on mixing two liquid alloys of precisely controlled chemistry and temperature in order to produce a predetermined alloy composition. In this study, the CDS was employed to prepare hypereutectic Al-20%Si(mass fraction) alloy using Al-30%Si and pure Al of different temperatures. The mixing rate was controlled using three small crucibles with a hole of different diameters in their bottom. The effect of mixing rate and temperature on the microstructure of the primary Si-phase during the mixing of molten Al and Al-30%Si was studied. The results showed that when the diameter of the small crucible bottom hole is 16 mm, a higher mass mixing rate 0.217 kg·s-1 would results in a lower stream velocity 0.414 m·s-1. Conversely a lower mass mixing rate 0.114 kg·s-1(the diameter of the small crucible bottom hole is 8 mm) would result in a higher fluid stream velocity 0.879 m·s-1. A lower mass mixing rate would be better to refine the primary Si than a higher mass mixing rate. Meanwhile, the morphology and distribution of primary Si could also be improved. Especially, when Al-30%Si alloy at 820 °C was mixed with pure Al at 670 °C in the case of a mass mixing rate of 0.114 kg·s-1 and a pouring temperature of 680 °C, the average size of the primary Si phase would be only 18.2 μm. Its morphology would mostly be octahedral and the primary Si would distribute uniformly in the matrix microstructure. The lower mass mixing rate(0.114 kg·s-1) will enhance the broken tendency of Al-30%Si steam and the mixing agitation of resultant melt, so the primary Si phase can be better refined.

Microstructure Characteristics and Apparent Viscosity of Hypereutectic Al-24%Si Alloy Melt During Semi-solid State Stirring

The microstructural evolution and apparent viscosity of hypereutectic Al-24%Si alloy during semi-solid state shearing were studied with a Searte type viscometer. When the alloy melt was continuously stirred from 720 degreesC to eutectic temperature, the primary Si crystals were gradually changed from elongated platelets to near-spherical shapes. It was found that some nondendritic a-phase formed when the melt was stirred below 585 degreesC. The experiment showed that the semi-solid stirring had strong effect on inhibiting the anisotropic growth of Si crystals during solidification. The apparent viscosity of the alloy melt increased slowly with the decreasing of temperature before the formation of nondendritic alpha -phase, which caused the dramatic increase of apparent viscosity.

Effect of Nd on Microstructure and Mechanical Properties of Hypereutectic Al-25Si Alloy

The modification mechanism of Nd on Al-25Si alloy was studied. The result showed that pure Nd (0.3%) could significantly refine primary silicon in hypereutectic Al-25Si alloy. And the morphology of primary silicon was transformed from star-shaped to block and the size of primary silicon changed from 150～200 μm to 40～80 μm after modification. The morphology of silicon and elements presence was detected by means of SEM-EDS, XRD was carried out to detect the phase constitution before and after modification. It was found that no new phase formed and the lattice of silicon and aluminum increased after modification and most of Nd may exist as solids solute element of silicon and absorb on the surface of silicon. Mechanical property test results showed that after modification with 0.3% Nd, Tensile strength increased about 33% from 138 to 184 MPa, yield strength increased about 15% from 126 to 145 MPa, and elongation change was not obvious. The improvement of mechanical property should attribute to fine grain strength and purification of base metal after modification.

Effect of complex modification of Al-5Ti and Al-3P on hypereutectic Al-18Si alloys

The solidification microstructure,fracture morphologies,and mechanical properties of an Al-18Si alloy and alloys modified with Al-5Ti and Al-3P master alloys were investigated using an optical microscope,scanning electron microscope,and an electronic universal testing machine.The results show that additions of Al-5Ti and Al-3P have significant effects on the size and area fraction of the primary Si and the mechanical properties of the Al-18Si alloy.Compared to the Al-18Si alloy modified with 0.6 wt%Al-5Ti at 850°C,when the Al-18Si alloy was modified with 0.3 wt%Al-5Ti and 0.5 wt%Al-3P at the same temperature,the average size of the primary Si decreased from 39 to 14μm and the area fraction increased from 9.5%to 11.6%.The biggest influencing factor on the tensile strength and elongation of the Al-18Si alloy is the addition of Al-3P,followed by the modification temperature and the addition of Al-5Ti.At a modification temperature of 850°C,the tensile strength and elongation of the Al-18Si alloy modified with 0.3 wt%Al-5Ti+0.5 wt%Al-3P increased by 19.6%and 88.6%,respectively compared to that of the Al-18Si alloy modified with 0.6 wt%Al-5Ti.

Effect of mixed rare earth oxides and CaCO_3 modification on the microstructure of an in-situ Mg_2Si/Al-Si composite

The effects of mixed rare earth oxides and CaCO3 on the microstructure of an in-situ Mg2Si/Al-Si hypereutectic alloy composite were investigated by optical microscope,scanning electron microscope,and energy dispersive spectrum analysis. The results showed that the morphol-ogy of the primary Mg2Si phase particles changed from irregular or crosses to polygonal shape,their sizes decreased from 75 μm to about 25 μm,and the compound of both the oxide and CaCO3 was better than either the single mixed rare earth o...

Characterization of high-pressure die-cast hypereutectic Al-Si alloys based on microstructural distribution and fracture morphology

The fracture behavior of high-pressure die-cast hypereutectic(HPDC) Al-Si alloys was investigated using a high-resolution laboratory CT and synchrotron X-ray tomography with a particular focus on the influence of HPDC microstructure. Results showed that microstructure of the alloy was mainly comprised of primary silicon particles(PSPs), Al dendrites, Cu-rich phases and pores. Most of the coarse PSPs, Cu-rich phases and pores were located in the center of the specimen. The rapid solidification of HPDC led to a heterogeneous microstructural feature. Elemental Cu was enriched in the frontiers of solid-liquid interface, causing the formation of large size dendritic arms. The pores were formed in the interdendrites which endured high stress intensity under high applied stress. Microcracks were originated from pores and further connected Cu-rich phases causing intergranular fracture. PSPs worked as obstacles causing piling-up dislocations in the phase interface. In the regions where large size of PSPs enriched in, PSPs ruptured rather than debonded from matrix, indicating transgranular fractures of PSPs. Microcracks originated around pores and PSPs tended to converge on the main cracks to decrease the energy required for crack propagation.

Microstructural characteristics of Al-20Si-2Cu-0.4Mg-1Ni alloy formed by rheo-squeeze casting after ultrasonic vibration treatment

A swash plate for air conditioning compressor of cars was formed by rheo-squeeze casting with semi-solid Al-Si alloy slurry prepared by ultrasonic vibration process, and the microstructure of this alloy was investigated. Besides the microstructures of primary Si particles and α(Al)+β-Si eutectic phases, non-equilibrium α(Al) particles or dendrites are discovered in the microstructure of the Al-20Si-2Cu-0.4Mg-1Ni alloy. Rapid cooling generated by squeeze casting process rather than the pressure is considered as the main reason for the formation of non-equilibrium α(Al) phase. The sound pressurizing effect of ultrasonic vibration also enables the non-equilibrium α(Al) phases to form above eutectic temperature and grow into non-dendritic spheroids in the process of semi-solid slurry preparation. Non-equilibrium α(Al) phases formed in the hypereutectic Al-Si alloy with ultrasonic vibration treatment, consist of round α(Al) grains formed above the eutectic temperature and a small amount of fine α(Al) dendrites formed under the eutectic temperature. The volume fraction of primary Si particles is decreased significantly by the effect of ultrasonic vibration through increasing the solid solubility of Si atoms in α(Al) matrix and decreasing the forming temperature range of primary Si particles. The average particle diameter and the volume fraction of primary Si particles in microstructure of the swash-plate by rheo-squeeze casting are 24.3 μm and 11.1%, respectively.

Wear behavior of Mg-10Y-4Gd-1.5Zn-0.4Zr alloy

Dry sliding wear tests were performed on a Mg-10Y-4Gd-1.5Zn-0.4Zr alloy using a Ball-on-Flat type wear apparatus against an AISI 52100 type bearing steel ball counterface. The wear rates were measured within a load range of 3-25 N, a sliding speed range of 0.03-0.3 m/s and a sliding temperature range of 25-200 ℃ at a constant sliding distance of 400 m. The morphologies of the worn surfaces and wear debris were studied by scanning electron microscopy （SEM） and energy dispersive X-ray spectroscopy （EDS）. Comparatively, the wear properties of a hypereutectic Al-Si aluminium alloy under the same condition were measured. The results indicate that the wear rates of Mg-10Y-4Gd-1.5Zn-0.4Zr alloy are lower than that of cast＋T6 AC9B aluminium alloy. The dominant mechanism of cast＋T6 Mg-10Y-4Gd-1.5Zn-0.4Zr alloy is abrasion wear mixed with other wear mechanisms, which tends to be an abrasion and plastic deformation wear at high normal load such as 10-25 N, abrasion and plastic deformation wears with small participation of delamination and oxidative wears at high sliding speed such as 0.12-0.3 m/s, and an oxidative and abrasion wear at high test temperature such as 100-200 ℃. The Mg12Y1Zn1 phase in Mg-10Y-4Gd-1.5Zn-0.4Zr alloy plays an important role in the wear rate.