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.

Effect of molybdenum on the microstructure and wear resistance of hypoeutectic Fe-Cr-B-C hardfacing alloys

Hypoeutectic Fe-Cr-B-C hardfacing alloys with different molybdenum( Mo) contents( The design content was 0,2,3. 3 and 4. 5 wt. %,respectively) were deposited using the flux-cored wire by means of metal active gas arc welding. The effects of Mo on the refinement of microstructures,eutectic microstructure changes and improvement of wear resistance were investigated. The main results were shown as follows: the added Mo could increase the volume fraction of eutectic microstructure and reduce the size of coarse primary austenite as well as the volume fraction. The carboboride of M3( B,C) could be observed in hypoeutectic Fe-Cr-B-C hardfacing alloys at the Mo design content of ≤2. 0 wt. %,while that of M23( B,C)6was formed when 3. 3 wt. % Mo was added.Additionally,the wear resistance of alloys was increased with the increase in Mo content. Specifically,the highest wear resistance of alloys was achieved at 4. 5 wt. % Mo design content,which was 113. 7% higher than that in alloys without Mo.

REFINING EFFECT OF BORON ON THE EUTECTIC SILICON IN HYPOEUTECTIC AlSi ALLOYS

The effect of boron on the eutecticsilicon in hypoeutectic Al Si alloys has been studied withXRDand SEM. Thefindingindicatesthatboron hasastrong refining effecton eutecticsili con . AlB2 formed by boron additionto Al Si meltsactasthe nucleusofeutecticsilicon which leadstotherefinementofeutecticsilicon.

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.

Model of Primary Austenite Dendrite Structure in Hypoeutectic Cast Iron

The solidification of primary austenite in hypocutcctic gray cast iron was studied by stepped grinding and quantitative metallography.The dendrite structure of primary austenite can be described by three models:typical dendrite crystal model,metamorphic dendrite crystal model and network dendrite crystal model.The dendrite crystals formed according to 3rd model is much more than those formed according to other models in this experiment.The primary austenites are connected each other,and the primary stems of austenite could be regarded as secondary arms and vice versa.

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.

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%).

The characterization of Fe-rich phases in a high-pressure die cast hypoeutectic aluminum-silicon alloy

Both microstructural characteristics and fracture behavior of Fe-rich phases in a high-pressure die-cast hypoeutectic Al-Si alloy were investigated.Attention was focused on the morphology and formation mechanism of Fe-rich phases,together with their influence on fracture.Results show that primary Ferich phases exhibited in blocky shape precipitated from liquid while secondary Fe-rich phase in a large net shape was distributed along eutectic boundary participating in a ternary eutectic reaction.Through synchrotron X-ray tomography characterization,three Fe-rich phases with different morphologies,i.e.,polyhedral shape,fine compact shape and Chinese script-type shape were extracted along the radial direction.Lower slow-shot speed promoted the polyhedral Fe-rich phase to precipitate in slow-shot sleeve while decreased the formation of fine compact and Chinese script-type Fe-rich phases in die cavity.Because of a worse deformation compatibility,polyhedral Fe-rich phases fractured and became stress concentration sources before the failure of the casting.

Effect of a High Magnetic Field on the Microstructure During Directionally Solidified Sn-20wt.%Pb Hypoeutectic Alloy

The microstructures of Sn-20wt.%Pb hypoeutectic alloy directionally solidified under a longitudinal magnetic field were investigated.The results show that the application of a high magnetic field has a great influence on the morphology of primary β-Sn phase at a temperature gradient of G_L=52 K/cm.At a certain growth speed,with the increase of magnetic field intensity,the magnetic field causes the primary β-Sn phase irregular and to be deformed,further,the magnetic field promotes the columnar to equaixed transition(CET).Further,the thermoelectric magnetic force(TEMF) imposed on the dendrite under a high magnetic field has been calculated and the results show that the numerical magnitude of the TEMF during directional solidification under a 10 T high magnetic field is about 10~4N/m^3 and this force should be responsible for the occurrence of the CET in the Sn-Pb alloy.This may act as an experimental proof that the coupling of temperature gradient and high magnetic field will induce the occurrence of the CET in Sn-Pb alloy.Above phenomena may be attributed to the thermoelectric magnetic force(TEMF)in solid.

Pre-peak on the structure factor of liquid hypoeutectic Al-Fe alloy

Using a θ-θ X ray diffractometer the structure of liquid hypoeutectic Al Fe alloy at 675℃ and its change with different thermal histories are investigated . Liquid Al is used as a reference system. It is found that a pre peak appears on the small angle part of the structure factor of the nonsuperheated hypoeutectic Al Fe alloy, but disappears after superheating whereas the structure factors of liquid Al hardly change with the different thermal histories, and no pre peak can be observed on them. The appearance of a pre peak is a mark of the intermediate range order (IRO). The pre peak is taken as the correlation between Fe atoms on the IRO length scale. Assume that the crystalline structure is the first order approximation of the liquid structure. A model structure is constructed. The basic unit is a cube formed by 8 Al atoms on its corner and one Fe atom occupying its center. The translation of such a unit along its fourbody diagonals by the length of a diagonal can meet the requirement of the Fe_Fe distance and gives a DO 3 like structure. If the vacancy among the units is filled with fcc like Al cells, the composition of the entity is about Al 7Fe, close to that of the metastable phase Al 6Fe from rapid solidification. It is speculated that there are Al 6Fe like clusters in the liquid hypoeutectic Al Fe alloy.

Effect of Carbon on Grain Boundary Segregation of Phosphorus and Phosphorus-Induced Intergranular Fracture in High Purity Iron with Phosphorus

The solidification of primary austenite in hypoeutectic gray cast iron was studied by stepped grinding and quantitative metallography. The dendrite structure of primary austenite can be described by three models: typical dendrite crystal model, metamorphic dendrite crystal model and network dendrite crystal model. The dendrite crystals formed according to 3rd model is much more than those formed according to other models in this experiment. The primary austenites are connected each other, and the primary stems of austenite could be regarded as secondary arms and vice versa.

Comparative cyclic oxidation behaviour and effect of oxides on hardness of wear resistance coating alloys T-401 and T-900

The investigated alloys are newly developed Tribaloy alloys with enhanced crack and oxidation resistance over the traditional Tribaloy alloys.The cyclic oxidation performance and effects of complex oxides on the hardness of cobaltbased Tribaloy alloys T-401(hypoeutectic)and T-900(hypereutectic)were assessed.The results showed that T-900 alloy has a lower oxidation rate as compared to T-401 alloy at 800 and 1000℃,which attributed to the formation of dense continuous Cr2O3 layer with an upper thinner continuous layer of CoCr2O4 and NiCr2O4 oxides.At 1000℃,T-401 alloy exhibited poor oxidation resistance due to severe spallation after 3 cycles(45 h).After oxidation,T-900 alloy exhibits 98%and 18%lower mass gain than T-401 alloy at 1000 and 800℃,respectively.For T-900 alloy,relationship between mass gain and thickness of oxide layer revealed that mass will increase 0.162 mg/cm2 for every 1-μm increase in the oxides thickness.Internal SiO2 oxide was observed at 800 and 1000℃for both alloys.However,the extent of internal Si oxides increased with increasing oxidation temperature from 800 to 1000℃.Consequently,internal oxidation of Si led to the formation of Laves phase-depleted region near oxide/alloy interface in T-900 alloy at 1000℃.Thus,hardness of T-900 alloy decreased from 618 to 392 HV beneath the oxide/alloy interface at 1000℃,whereas hardness of T-900 and T-401 alloys after cyclic oxidation test at 800℃increased from 618 to 855 and 519 to 685 HV,respectively.

Microstructure and rheological properties of a semisolid A356 alloy with erbium addition

The effects of erbium addition on the rheological properties and microstructure of a semisolid A356 alloy were studied.The semisolid slurries were prepared through the serpentine channel technique before they were thixoformed using parallel-plate compre ssion with cylindrical discs.The grain and globule size decreases as the Er content increases,resulting in an improved and uniform distribution of spherical primaryα-Al phase within the semisolid slurry.The addition of the Er modifies the grain morphology and size of theα-Al grains,resulting in a better and more uniform distribution of spherical primaryα-AI phase within the semisolid slurry.As a result,rheocast quality index increases with the addition of Er,which is suitable for the thixoforming process.The A356 alloy without Er has the highest viscosity herein.The viscosity decreases,and the flow characteristics of the semisolid feedstock are expected to improve when Er is added as a result of the refinement of primary a-Al and modification of eutectic silicon.Furthermore,the refined semisolid A356 alloys with Er show a slightly larger fraction of highangle grain boundaries compared to that for the unrefined alloy.