Grain refining mechanism of Al-3B master alloy on hypoeutectic Al-Si alloys

Al-3B master alloy is a kind of efficient grain refiner for hypoeutectic Al-Si alloys. Experiments were carried out to evaluate the effect of undissolved AlB2 particles in Al-3B master alloy on the grain refinement of Al-7Si. It is found that the number and the settlement of AlB2 particles in the melt all have effect on the grain refining efficiency. On the basis of experiments and theoretical analysis, a new grain refinement mechanism was proposed to explain the grain refinement action of Al-3B on hypoeutectic Al-Si alloys. The formation of ＇Al-AlB2＇ shell structure is the direct reason for grain refinement and the undissolved AlB2 particles is the indirect nucleating base for subsequent α（Al） phase.

Grain refining technique of AM60B magnesium alloy by MgCO_3

The effects of grain refining parameters on microstructure of AM60B magnesium alloy with MgCO3 were investigated and then a refining technique was developed.Simultaneously,the corresponding mechanisms were discussed.The results indicate that increasing addition temperature of MgCO3 or pouring temperature is beneficial for obtaining fine grains.There is an optimal addition amount of 1.2%at the addition temperature of 790°C.Prolonging holding time at 790°C will increase grain size.The grain refining technique that 1.2%MgCO3 is added at 790°C followed by holding for 10 min and pouring can decrease the grain size from 348μm of the un-refined alloy to 69μm.The nucleation substrates are actually the Al4C3 particles formed from reactions between the MgCO3 and alloying elements in the melt.Besides the heterogeneous nucleation regime,growth restriction of the Al4C3 particles agglomerated at growing front is the other mechanism.

Effects of grain refining and modification on mechanical properties and microstructures of Al-7.5Si-4Cu cast alloy

Al-7.5Si-4Cu cast alloy melt modified by Al-5Ti-B, RE and Al-10Sr master alloys were poured in the chromite sand moulds, to investigate comparatively the effects of individual or combined additions of grain refiners and modifiers on the mechanical properties, microstructures, grain refining and modification, and intermetallic compounds of the alloy. The results show that the mechanical properties and the microstructures of Al-7.5Si-4Cu cast alloys are improved immensely by combining addition of 0.8%Al-5Ti-B, 0.1%RE and 0.1%Al-10Sr grain refiners and modifiers compared with the individual addition and cast conditions. For individual addition condition, addition of 0.8%Al-5Ti-B master alloy can obtain superior tensile strength, Brinell hardness and finer equiaxedα（Al） dendrites. The alloy with 0.1%RE master alloy shows the highest improvement in ductility because the rare earth can purify the molten metal and change the shape of intermetallic compounds. While the alloy with 0.1%Al-10Sr modifier shows only good improvement in yield strength, and the improvement of other performance is unsatisfactory. The Al-10Sr modifier has a significant metamorphism for the eutectic silicon, but will make the gas content in the aluminum alloy melt increase to form serious columnar grain structures. The effects of grain refining and modification on mean area and aspect ratio have the same conclusions obtained in the mechanical properties and the microstructures analyses.

Grain refining effect of Mg by novel particle cluster-containing Al-Ti-C master alloy

A novel A1-Ti-C master alloy containing A14C3 and TiC particle clusters, which exhibits great refining potential for Mg, was prepared. With the addition of 2% A1-Ti-C master alloy, the grains transform to equiaxed crystal with a diameter of （110-a：17） ~tm. The results indicate that A14C3 and TiC particle cluster, rather than a single particle, plays an important role in the refining process. Compared with the simplex smooth nucleating substrate, concave regions on the particle cluster provide easier route for the transformation from liquid Mg atoms to stable nucleus. Nucleus with a small size can also reach the critical nucleation radius when they attach on the concave regions of the substrate. A14C3 and TiC particle clusters thus become more favorable nucleating substrate for a-Mg grains.

A review:Past,present and future of grain refining of magnesium castings

Magnesium is the lightest constructional metal,which makes it an important material for different applications like automotive,transportation,aviation and aerospace.There are several studies about developing properties of existing Mg alloys and introducing new alloy systems to industrial producers.An important way to improve properties of metallic materials is to decrease grain size that results almost in increasing all kind of properties of the material.This review paper aims to summarize the literature about grain refining of magnesium alloys.The text is consisting of three sections,which focused on the(1)grain refining methods used in the past,which are not used today,(2)grain refining methods currently being used in the industry and(3)novel and newly developed methods that may find usage in the industry in future.Before explaining grain refining methods of magnesium alloys a general summary about grain refinement of metals is also provided.

Grain refining and property improvement of AZ31 Mg alloy by hot rolling

Hot rolling of AZ31 Mg alloy was performed by using as-cast alloy ingot as the starting material.The microstructures and mechanical properties of the as-rolled alloy subjected to various rolling passes were investigated.The results show that the grain size of the alloy can be refined steadily with increasing rolling passes by dynamic recrystallization.With the steady refining of the grain size,both the mechanical strength and the plasticity of the alloy are improved correspondingly.In particular,when the grain size is reduced to about 5μm after 5 rolling passes,the yield strength,ultimate tensile strength and tensile fracture strain of the alloy are 211 MPa,280 MPa and 0.28 in the transverse direction,they are 200 MPa,268 MPa and 0.32 in the rolling direction,respectively.

EFFECT OF GRAIN REFINING ON FATIGUE-CREEP INTERACTION BEHAVIOURIN A Ni-BASE SUPERALLOY

The fatigue-creep interaction behaviour of superalloy GH698 with different grain sizes has been studied at 700℃.The results show that three zones,F,C and FC,can be distinguished at the fatigue-creep interaction curves.In zones FC and C,the presence of alternative stresses inhibits the creep deformation process therefore delays the fracture of the alloy.This effect will be enhanced by grain refining.However,in zone F,grain refining exhibits an inverse ef fect under large alternative stresses.

Effect of ECAE Preheating on Grain Refining of Nickel-Titanium Alloy

The influence of equal channel angular extrusion preheating on the microstructure of NiTi was examined. Temperatures under non-isothermal condition is 750, 850 and 950 ℃, and ram speed was 25 mm·s^(-1). The micrographs showed that processing by each of the three temperatures via ECAE can refine the initial coarse grains of NiTi (as-received) after the first pass, and the developments of microstructure were quite different under different hot-working conditions. The influence of ECAE preheating (including temperature and time) on the microstructure of nickel-titanium was analyzed.

Grain refining action of Ti existing in electrolytic low-titanium aluminum with Al-4B addition for superheated Al melt

The effects of superheating temperature on the grain refining efficiency of Ti existing in electrolytic low-titanium aluminum(ELTA)without and with the Al-4B addition and the Al-5Ti-1B master alloy in pure Al were comparatively investigated. The results show that the Ti existing in ELTA without Al-4B addition exhibits a certain grain refining efficiency when the melt superheating temperature is lower,but the efficiency decreases rapidly when the superheating temperature is higher.The grain refining efficiency of the Al-5Ti-1B master alloy is better than that of the Ti existing in ELTA without Al-4B addition at any superheating temperature,but it also decreases obviously with the increase of the superheating temperature.One important reason is that the TiB2 particles coming from the Al-5Ti-1B master alloy can settle down at the bottom of the Al melt easily when the superheating temperature is increased,thus decrease the number of the potent heterogeneous nuclei retained in the Al melt.If the Al-4B master alloy is added to the ELTA melt,the grain refining efficiency of the Ti existing in ELTA can be improved significantly, and does not decrease with the increase of the superheating temperature.This perhaps provides us a possible method to suppress the effect of the superheated melt on the microstructures of aluminum..

Grain Refining Performance of SHS Al-50TiC Master Alloys for Commercially Pure Aluminum

An Al 50wt%TiC composite was directly synthesized by self propagating high temperature synthesis (SHS) technology,and then was used as a grain refining master alloy for commercially pure aluminum.The microstructure and grain refining performance of the synthesized master alloy were emphatically investigated.The SHS master alloy only contained submicron TiC particles except for Al matrix.Moreover,TiC particles were relatively free of agglomeration. Grain refining tests show that adding only 0.1 wt% of the master alloys to the aluminum melt could transform the structure of the solidified samples from coarse columnar grains to fine equiaxed grains (average grain size 120μm),and that this grain refining effectiveness could be maintained for almost 1.5h at 1003K. Therefore,it is concluded that the SHS master alloy is an effective grain refiner for aluminum and its alloys, and that it is highly resistant to the grain refining fading encountered with most grain refiners.

Discussion on grain refining mechanism of AM30 alloy inoculated by MgCO_(3)

AM30 was inoculated by MgCO_(3) powder with different holding time.The influence of MgO decomposed by MgCO_(3)on the grain refinement effect was mainly discussed in the present study.Three sets of comparative samples were prepared.They were AM30 alloy inoculated by MgO and pure Mg inoculated by MgO and MgCO_(3).The possible nucleating particles were observed and analyzed by EPMA and SEM.AM30 alloy could be effectively refined by either MgCO_(3)or MgO inoculation.Grain refining efficiency and fading effect of MgO inoculation were better than those of MgCO_(3) inoculation.However,pure Mg could not be refined by these two inoculants.Al is an indispensable element to determine the grain refinement of Mg alloys inoculated by either MgCO_(3)or MgO.MgO should not be the effective substrates forα-Mg phase.A novel grain refining mechanism of MgCO_(3) inoculation on AM30 alloy was proposed by combining experimental results with theoretical calculation,i.e.,MgAl_(2)O_(4) should be the potent nuclei ofα-Mg grain for the AM30 alloy in addition to Al_(4)C_(3).

Grain refining technique of AM60B alloy by Al-Ti-B master alloy

The effects of grain refining parameters on grain size of AM60B magnesium alloy have been investigated using an Al-5Ti-IB master alloy as refiner; and an appropriate refining technique has been developed. The results indicate that the Al-Ti-B master alloy is an effective grain refiner for AM60B alloy and the grain size can be decreased from 348 μm to 76 μm. Raising the addition temperature or the poudng temperature is beneficial for grain refinement; while for the addition amount and holding time, there is an optimal value. The appropriate grain refining technique is that 0.3% Al-Ti-B master alloy is added at 780℃ and then the melt is held for 30 min before pouring. The above phenomena can be explained by the refining mechanisms that have been proposed from the related studies on Al and Mg alloys and theoretical analysis.

Grain refining in weld metal using short-pulsed laser ablation during CW laser welding of 2024-T3 aluminum alloy

The 2024 aluminum alloy is used extensively in the aircraft and aerospace industries because of its excellent mechanical properties.However,the weldability of 2024 aluminum alloy is generally low because it contains a high number of solutes,such as copper(Cu),magnesium(Mg),and manganese(Mn),causing solidification cracking.If high speed welding of 2024 aluminum alloy without the use of filler is achieved,the applicability of 2024 aluminum alloys will expand.Grain refining is one of the methods used to prevent solidification cracking in weld metal,although it has never been achieved for high-speed laser welding of 2024 aluminum alloy without filler.Here,we propose a short-pulsed,laser-induced,grain-refining method during continuous wave laser welding without filler.Bead-on-plate welding was performed on a 2024-T3 aluminum alloy at a welding speed of 1 m min−1 with a single mode fiber laser at a wavelength of 1070 nm and power of 1 kW.Areas in and around the molten pool were irradiated with nanosecond laser pulses at a wavelength of 1064 nm,pulse width of 10 ns,and pulse energy of 430 mJ.The grain-refinement effect was confirmed when laser pulses were irradiated on the molten pool.The grain-refinement region was formed in a semicircular shape along the solid–liquid interface.Results of the vertical section indicate that the grain-refinement region reached a depth of 1 mm along the solid–liquid interface.The Vickers hardness test results demonstrated that the hardness increased as a result of grain refinement and that the progress of solidification cracking was suppressed in the grain refinement region.

The grain refining mechanism of C-Mn steel by CSP

The grain refining mechanism of C-Mn steel sheet on compact strip production(CSP) line was investigated in this study.The grain was about 100μm after F1 pass and decreased all the way of the rolling process(F2-F6) to 15μm.Repeated phase transformation experiment was conducted to the steel for grain refinement.The phase transformation at 860℃and 920℃can refine the grain size to 7.5μm.

Enhanced Grain Refining Effect of Mg–Zr Master Alloy on Magnesium Alloys via a Synergistic Strategy Involving Heterogeneous Nucleation and Solute‑Driven Growth Restriction

Zirconium(Zr)emerges as the most effective grain refiner for magnesium(Mg)alloys incorporating Zr.Typically,Zr is introduced in the form of an Mg–Zr master alloy.However,within Mg–Zr master alloys,Zr predominantly exists in a particle form,which tends to aggregate due to attractive van der Waals forces.The clustered Zr is prone to settling,thereby reducing its refining impact on Mg alloys.In this work,a combined pretreatment process for Mg–Zr master alloys was proposed,encompassing the introduction of a physical field to intervene the agglomeration of particle Zr and the employ of high-temperature dissolution and peritectic reactions to promote the solid solution of Zr.The results demonstrate that the particle Zr within the pretreated Mg–Zr master alloy is effectively dispersed and refined,and greater solute Zr levels can be achieved.The subsequent grain refinement ability was studied on a typical Mg–6Zn–0.6Zr(wt%)alloy.The outcome highlights that an improvement in the grain refinement efficacy(32.4%)of Mg–Zr master alloys was obtained with a holding time of 60 min.The pretreated Mg–Zr master alloy significantly augments the efficiency of grain refinement for Mg alloys through a synergistic strategy involving heterogeneous nucleation and solute-driven growth restriction.The crucial factor in achieving effective grain refinement of Zr in Mg alloys lies in regulating the presence and morphology of Zr in the Mg–Zr master alloy,distinguishing between particle Zr and solute Zr.This study introduces a novel method for developing more efficient Mg–Zr refiners.

Grain refinement of Mg-Ca alloys by native MgO particles

In Mg-Ca alloys the grain refining mechanism,in particular regarding the role of nucleant substrates,remains the object of debates.Although native MgO is being recognised as a nucleating substrate accounting for grain refinement of Mg alloys,the possible interactions of MgO with alloying elements that may alter the nucleation potency have not been elucidated yet.Herein,we design casting experiments of Mg-xCa alloys varied qualitatively in number density of native MgO,which are then comprehensively studied by advanced electron microscopy.The results show that grain refinement is enhanced as the particle number density of MgO increases.The native MgO particles are modified by interfacial layers due to the co-segregation of Ca and N solute atoms at the MgO/Mg interface.Using aberration-corrected scanning transmission electron microscopy and electron energy loss spectroscopy,we reveal the nature of these Ca/N interfacial layers at the atomic scale.Irrespective of the crystallographic termination of MgO,Ca and N co-segregate at the MgO/Mg interface and occupy Mg and O sites,respectively,forming an interfacial structure of a few atomic layers.The interfacial structure is slightly expanded,less ordered and defective compared to the MgO matrix due to compositional deviations,whereby the MgO substrate is altered as a poorer template to nucleate Mg solid.Upon solidification in a TP-1 mould,the impotent MgO particles account for the grain refining mechanism,where they are suggested to participate into nucleation and grain initiation processes in an explosive manner.This work not only reveals the atomic engineering of a substrate through interfacial segregation but also demonstrates the effectiveness of a strategy whereby native MgO particles can be harnessed for grain refinement in Mg-Ca alloys.

Strength and plasticity improvement induced by strong grain refinement after Zr alloying in selective laser-melted AlSiMg1.4 alloy

In order to enhance the mechanical properties of the selective laser-melted(SLM) high-Mg content AlSiMg1.4 alloy,the Zr element was introduced.The influence of Zr alloying on the processability,microstructure,and mechanical properties of the alloy was systematically investigated through performing microstructure analysis and tensile testing.It was demonstrated that the SLM-fabricated AlSiMg1.4-Zr alloy exhibited high process stability with a relative density of over 99.5% at various process parameters.Besides,the strong grain refinement induced by the primary Al3Zr particle during the melt solidification process simultaneously enhanced both the strength and plasticity of the alloy.The values for the yield strength,ultimate tensile strength,and elongation of the SLM-fabricated AlSiMg1.4-Zr were(343±3) MPa,(485±4) MPa,and(10.2±0.2)%,respectively,demonstrating good strengthplasticity synergy in comparison to the AlSiMg1.4 and other Al-Si-based alloys fabricated by SLM.

Application of novel constrained friction processing method to produce fine grained biomedical Mg-Zn-Ca alloy

In order to obtain Mg alloys with fine microstructures and high mechanical performances,a novel friction-based processing method,name as“constrained friction processing(CFP)”,was investigated.Via CFP,defect-free Mg-Zn-Ca rods with greatly refined grains and high mechanical properties were produced.Compared to the previous as-cast microstructure,the grain size was reduced from more than 1 mm to around 4μm within 3 s by a single process cycle.The compressive yield strength was increased by 350%while the ultimate compressive strength by 53%.According to the established material flow behaviors by“tracer material”,the plastic material was transported by shear deformation.From the base material to the rod,the material experienced three stages,i.e.deformation by the tool,upward flow with additional tilt,followed by upward transportation.The microstructural evolution was revealed by“stop-action”technique.The microstructural development at regions adjacent to the rod is mainly controlled by twinning,dynamic recrystallization(DRX)as well as particle stimulated nucleation,while that within the rod is related to DRX combined with grain growth.

Effect of addition temperature on dispersion behavior and grain refinement efficiency of MgO introduced into Mg alloy

The effect of addition temperature of MgO particles(MgOp)on their dispersion behavior and the efficiency of grain refinement in AZ31 Mg alloy was investigated.In addition,the grain refinement mechanism was systematically studied by microstructure characterization,thermodynamic calculation,and analysis of solidification curves.The results show that the grain size of AZ31 Mg alloy initially decreases and then increases as the MgOp addition temperature is increased from 720 to 810℃,exhibiting a minimum value of 136μm at 780℃.The improved grain refinement efficiency with increasing MgOp addition temperature can be attributed to the reduced Mg melt viscosity and enhanced wettability between MgOp and Mg melt.Furthermore,a corresponding physical model describing the solidification behavior and grain refinement mechanism was proposed.

Differences of grain-refining effect of Sc and Ti additions in aluminum by empirical electron theory analysis

The differences of grain-refining effect between Sc and Ti additions in aluminum,which cannot be substantially explained by traditional theories,were carefully studied.The empirical electron theory(EET) of solids and molecules was employed to calculate the valence electron structures(VES) of Al3Ti and Al3Sc.The conclusions can be drawn that,in the two alloys Al-Ti and Al-Sc,the different valence electron structures of Al3Ti and Al3Sc and the consequent differences of growth habit of the two particles,and the different interfacial electron density between particles and matrix fundamentally lead to the differences of grain-refining effect between Sc and Ti additions on aluminum and make Sr the better grain-refiner of aluminum.