Chilled Layer Research Articles

Study on Processing Conditions for Semi-Solid Forging of Magnesium Alloys

Magnesium alloy castings are mainly formed by the die casting method, but this method has the disadvantage that product properties such as strength vary due to many defects inherent in casting. In this study, AZX912 (a flame-retardant magnesium alloy with 2% calcium added to AZ91D alloy) was semi-solid forged using a servo press and die cushion system to stabilize product properties. Experiments were conducted to refine the α-phase and reduce the yield point, and the stirring speed was changed and its effect was investigated. Observation of the microstructure of the molded product using an optical microscope showed that the average grain size of the α-phase became smaller as the stirring speed increased. Tensile tests were conducted on specimens cut from the compacts, and the yield point increased as the stirring speed increased. This is thought to be due to compliance with Hall Petch's law. The microstructure of the molded product was observed under an optical microscope and showed a three-layer structure with a dendrite shape in the upper part (about 5%), a grain structure in the middle part (over 90%), and a chill layer in the lower part (less than 5%). Comparison of the thickness of the chill layer showed that the thickness of the chill layer decreased as the solidus ratio increased.

The formation mechanism of the chill fine-grain layer with high supersaturation and its influence on the mechanical properties of die casting Al-7Si-0.5Mg alloy

In this study, the chill layer with high supersaturation was observed on the surface of the Al-7Si-0.5Mg die casting tensile samples. The optional microstructure and electron backscatter diffraction (EBSD) results show that the chill layer has fine α-Al grains (≈5 μm). There is a solution gradient in die-casting aluminum alloy and the chill fine-grain layer is in a supersaturated state. The pre-solidified dendrites (PSDs) formed in the shot sleeve and the nonuniform velocity distribution of the melt are responsible for the formation mechanism of the chill fine-grain layer with high supersaturation. Under high pressure and high injection speed, the PSDs will aggregate in the core of the samples due to the Magnus effect. Moreover, the chill layer with solute enrichment can be obtained as a result of rapid cooling and incoordinate solute distribution. Consequently, the tiny Mg2Si phase could precipitate spontaneously from the supersaturated α-Al grains in the chill layer, simultaneously improving the of strength and ductility.

Dependence of cast iron chill from its carbon equivalent

Numerical relation of cast iron chill characteristics (distance of chilled layer H and volume quota of ledeburite in it Qл ) with its carbon equivalent СE was investigared. This data helps to prognosticate with high probability the evolution of the surface chilled layer forming at the production of castings with different thickness from cast iron of various chemical compositions. The object of study is the unalloyed induction melted cast iron with eight variants of chemical composition with carbon equivalent from 3.30 up to 5.53 %. From these cast irons we made the step-by-step castings with steps sizes of 10×60 mm and thickness of 5, 10, 20 and 40 mm. The distance (depth) of chilled layer was measured at the fractures of the castings and gaged on thickness of full chill zone. Ledeburite volume quota was detected by metallographic method using “Nexsys-Image expert pro 3” computer program. According to experimental data, when the casting thickness is 5 and 10 mm the through (at all thickness) full chill is formed at carbon equivalent ≤ 4.08 % and ≤ 3.67 % consequently. At the castings with 20 and 40 mm thickness the zone of full chill is absent, and in this case the chilled layer depth increases with a decrease of carbon equivalent and decreases with an increase of casting’s thickness X. The dependence of H from СЕ have the exponential character and can be described by the equation H = A exp (–k СE ), where A and k are empirical coefficients. Ledeburite volume quota near the contact surface of casting with chiller is near 90 %, but with an increase in the distance from the surface it decreases with different intensity depending on changes of carbon equivalent and casting’s thickness. By mathematical processing of the experimental data received for the distance of 5 mm from the contact surface of the casting with chiller, we have detected that numerical re lation Qл in casting chilled layer with value of CE can be described by the exponential dependence

Dependence of Cast Iron Chill from its Carbon Equivalent

The numerical relation of cast iron chill characteristics (distance of chilled layer H and volume quota of ledeburite in it Ql) with its carbon equivalent СE was investigated. This data helps forecast the evolution of the surface chilled layer forming at the casting production with different thickness from cast iron of various chemical compositions. The study focuses on the unalloyed induction-melted cast iron with eight chemical-composition variants with carbon equivalent from 3.30 up to 5.53%. From these cast irons, step-by-step castings were made with steps sizes of 10 × 60 mm and thickness of 5, 10, 20, and 40 mm. The chilled-layer distance (depth) was measured at the casting fractures and gaged on thickness of full chill zone. Ledeburite volume quota was detected by a metallographic method using the “Nexsys-Image expert pro 3” computer program. According to experimental data, when the casting thickness is 5 and 10 mm, the through (at all thickness) full chill is formed at a carbon equivalent ≤4.08% and ≤3.67%, consequently. At the castings with 20- and 40-mm thickness, the zone of full chill is absent. In this case, the chilled layer depth increases with a decrease of carbon equivalent and decreases with an increase of casting’s thickness X. The dependence of H from CE have the exponential character and can be described by the equation H = Aexp(–kCE), where A and k are empirical coefficients. Ledeburite volume quota near the contact casting surface with chiller is near 90%, but it decreases with different intensity depending on changes of carbon equivalent and casting’s thickness with an increase in the distance from the surface. By mathematical processing of the experimental data received for the 5-mm distance from the contact surface of the casting with chiller, a numerical relation Ql in casting chilled layer with value of CE can be described by the exponential dependence: Ql = 1000(7/(X + 10))exp(–CE).

Recent Advances in Cast Iron Structure and Properties Ultrasonic Testing and Flaw Detection

The advantage of ultrasonic testing of iron castings prior to destructive control consists of an impressive reduction in time and costs, as well as the ability to assess the quality of the metal anywhere on the castings. According to the acoustic characteristics of cast iron it is possible to determine the form of graphite in it and its strength. The presence of chill in the metallic base and the thickness of the chilled layer is also determined by ultrasonic method. The use of electronic signal processing allows to distinguish it from high structural noise, which makes possible the testing of cast iron for a thickness of several meters. The use of transducers with phased array is the basis of the flaw detection of containers for nuclear waste from cast iron with globular graphite with a thickness of 500 mm.

Formation behaviours of blowhole and chill layer by GTAW in cast iron

ABSTRACTCast irons have some excellent characteristics in wear resistance, vibrational damping etc., and are widely used in many industrial machinery applications. But, the weldability has been much inferior originated from its high-carbon content. Several researches have reported that some of the important factors affecting the weldability were formation of blowhole and chill layer during fusion welding and subsequent rapid cooling.In this study, the formation behaviours of those were investigated in both flake and nodular graphite cast irons. Tungsten inert gas arc welding was performed using several kinds of filler metal varied nickel and chromium content.The study was made by paying attention to carbon behaviour and influence of nickel and chromium in filler metal on it.Experimental results obtained were as follows.The amount of blowhole increased with nickel content and decreased with chromium content.On the other hand, the amount of chill layer increased with chromium content and decreased with nickel content.It was estimated that both blowhole and chill layer formation were related to activity and diffusivity changes of carbon affected by nickel and chromium content. Then consequently they have a correlation relationship each other.

Experimental investigation on chilled cast iron tappet manufacturing processes parameters

ABSTRACTChilled cast iron tappet has a tendency microstructure of white, mottled and gray iron. The exact composition and other casting parameters, like pouring temperature, inoculation and coating, need to be determined for achieving the desired thickness of the chilled layer. Chilled cast iron finds applications in areas where improved hardness and wear resistance are required. Mottled cast iron has very poor machinability and high brittleness due to the presence of secondary cementite. These constitute the limitations for its use. The influence of inoculation, pouring temperature, coating thickness and chill plate on chilled depth was investigated. Taguchi design-of-experiments (DOE) are used for generating an optimal set of casting parameters to obtain a satisfactory chilled depth. Analysis of the effects of all the parameters on chilled depth has been carried out through a microstructure study.

Experimental and Numerical Simulations of the Solidification Process in Continuous Casting of Slab

Thermal simulation equipment (TSE) was recently developed to simulate the solidification process in the industrial continuous casting of slab. The grain growth, solid-liquid interface movement, and columnar-to-equiaxed transition (CET) in the continuous casting process can be reproduced using this equipment. The current study is focused on the effects of different cooling rates and superheat conditions on the grain growth in the solidification process of chromium-saving ferritic stainless steel (B425). The temperature distribution and microstructure evolution are simulated by a Cellular Automaton-Finite Element (CAFE) model. The experimental results demonstrate that the temperature gradient and the grain growth rate of the sample can be effectively controlled by the equipment. It is observed from optical micrographs of the microstructure that the average equiaxed grain ratio increases when the superheat temperature decreases. The average equiaxed grain ratio is approximately 26% and 42% under superheat conditions of 40 °C and 30 °C, respectively, and no apparent columnar grain generation in the samples occurs under superheat conditions of 10 °C and 20 °C, as the result of a large thermal resistance at the copper-sample interface and low superheat inside the sample. A lower cooling rate results in a higher equiaxed crystal ratio in the sample. As the cooling rate decreases, the equiaxed crystal ratio becomes 14%, 23%, and 42%. Comparing the simulation results with the experimental observations, a reasonable qualitative agreement is achieved for the chilled layer thickness, grain morphology, and CET in the sample. Thus, the CAFE model in the current study can accurately predict the grain growth under different superheating and cooling rate conditions.

鋳鉄のティグ溶接におけるブローホールとチル層の形成挙動

鋳鉄のティグ溶接におけるブローホールとチル層の形成挙動

Study on microstructure of squeeze casting AZ91D alloy

The present paper reports the investigation of the microstructure distribution of squeeze cast AZ91D alloy. The microstructure of squeeze cast AZ91D alloy is not uniform and is composed of four zones, which are chilled layer, segregation zone, pressured crystallisation area and hot spot area respectively. Moreover, in the pressured crystallisation area, the microstructure sequence in the transverse section from the outside to the inside could be divided into four sublayers, such as fine equiaxial dendrite area, dendrite area with a high directivity, confusion dendrite area and disorder dendrite area. The volume fraction of the intermetallic compound Mg17Al12 also varied with the location. The volume fraction of Mg17Al12 in the pressured crystallisation area is the largest except in the segregated zone.

Relation between the chill formation on cast iron and the linear solidification rate

414 As a rule, a chill structure forms in the surface lay� ers of castings. This increases the surface hardness and wear resistance. Therefore, a surface layer of chill (white iron) is specially formed in the production of some castiron parts, such as rollingmill rollers, crushing and grinding components, and equipment for shaping refractories. However, the presence of chill at the surface of castings is usually regarded as cause for rejection, since it prevents their machining. Chill may be eliminated by heat treatment (annealing), but this complicates the technology and lengthens the production process. Therefore, it is important to study the formation of the chill layer at the surface of iron castings. The quantity of chill present is estimated from the thickness (depth) of the zones of pure or complete chill. The zone of complete chill includes a zone of pure white iron (with the chill structure) and a transi� tion layer (with a structure half consisting of white iron). The influence of technological factors on the depth of the chill has been studied repeatedly. Experiments show that the depth of the chill layer at the surface of castings is determined by many factors: the chemical composition of the iron; the batch composition; the smelting conditions; the conditions of ladle treatment and casting; and the cooling rate of the casting (1-3). However, the quantitative relation between the chill parameters and the casting conditions has not previ� ously been established.

Thermal erosion of felsic ground by the laminar flow of a basaltic lava, with application to the Cave Basalt, Mount St. Helens, Washington

The thermal erosion of cold felsic ground by the steady laminar flow of a hot basaltic lava is examined theoretically and experimentally. Initially, a chill layer is grown and then remelted at the base of the lava flow. A steady thermal erosion velocity is then established, which is limited by the buoyant instability of the melted ground or by the effective freezing temperature of the basaltic lava. When the theoretical analysis is applied to the longest lava tube system of the Cave Basalt on Mount St. Helens, it is found that about 100 days of flow is sufficient to produce the observed ground erosion in Little Red River, Ape and Lake Caves.

Inkdeath (review)

Reviewed by: Inkdeath Karen Coats Funke, Cornelia Inkdeath; tr. from the German by Anthea Bell. Chicken House/Scholastic, 2008 [704p] ISBN 978-0-439-86628-6 $24.99 Reviewed from galleys R Gr. 7–10 The hefty conclusion to the Inkheart trilogy begins, helpfully, with a map and summaries of the prior two books, and points to a character list in the back of the book. This is good, because the densely populated Inkworld has gotten no less crowded following the deaths of some of its choicest villains. Meggie, Mo, and Resa are now living with the band of robbers led by the Black Prince, and Mo is relishing his outlaw role as the notorious Bluejay—relishing it a bit too much for his daughter’s and pregnant wife’s taste, and indeed sometimes for his own, as it is quite a blood-splattered persona. Farid is still prostrating himself to Orpheus, badgering him to read Dustfinger back from the dead, while Orpheus himself is having a grand time making himself grand in this world of words that he, to some degree, controls. Indeed, Orpheus does find a way to bring Dustfinger back, by offering the Bluejay’s life in exchange, but Death makes a bargain of her own with the Bluejay: he must find the book he bound for the Adderhead, which has made him immortal but also causes his flesh to molder and decay, and write in it the three words that will kill him. Funke weaves her complicated plot with the multitextured threads of precarious alliances, crafty greed, thwarted attempts at entrapment, loneliness, betrayal, first and second love, and the complexities of filial affections and disaffections; the cloth she comes up with is rich and enveloping, rimed at times with a chill layer of grief, while at other times freckled with sparks of unabashed wonder and grisly violence. Could it have been edited and tightened, especially when the story turns to Fenoglio’s tedious writer’s block or Orpheus’ endless self-congratulations? Undoubtedly. But this is without question a book-lover’s book, from the quotations that frame each chapter and tempt the tastebuds for other books, to the unusual fantasy-frame ending that leaves the characters happily at home in their book rather than back in their real-world beds. Settle in and read. Copyright © 2008 The Board of Trustees of the University of Illinois

Modeling of Inclined Cooling Plate Semisolid Processing by Model Alloy

Continual improvement of product quality has been a long challenge to Semi-Solid Metal (SSM) technology. By conventional semi-solid processes, this might be attained at the expense of economical production. The advent of Inclined Cooling Plate (ICP) process has already realized the development of non-dendritic SSM while satisfying qualitative, quantitative and economical requirements collectively. In spite of its potential advantages, functional mechanisms of this process are not yet clearly understood that makes its optimal utilization obscured. Basically, such understanding needs a picture of the process. As the first step, this picture is pursued through physical modeling of the ICP process i.e. direct observation of an analog system by virtue of transparent character of a model alloy (succinonitrile-acetone). Based on this phenomenological model, a picture of the process is presented as follows: flowing molten alloy down ICP, multiple regions form typically on the plate i.e. a chilled layer at the vicinity of the plate surface, a two-phase mushy zone on the chilled layer and ambient liquid far from the plate surface. In this process, interaction of the liquid forced-flow with mushy zone separates solid particles from the stationary mush on the plate resulting in a two-phase mixture which is responsible for the formation of slurry i.e. SSM.

Characterization and Improvement in the Corrosion Performance of a Hot-Chamber Diecast Mg Alloy Thin Plate by the Removal of Interdendritic Phases at the Die Chill Layer

This work presents results concerning the effect of the die chill layer on the corrosion performance of a hot-chamber diecast AZ91D thin plate, with particular attention to the role of interdendritic phases (primary β (Al17Mg12) and surrounding α phase). The primary β phase in the die chill layer was removed by Ar+ etching, but the other main constituent phases remained on the surface of the sample. Although previous researchers have attributed intense galvanic corrosion to the cathodic phase (primary β), this work demonstrates that the removal of the primary β phase from the diecast sample surface did not improve the corrosion performance of the sample. Transmission electron microscope (TEM) examinations were performed, to elucidate the microstructure near the die chill surface, especially focusing on the α-Mg phase that surrounds the primary β phase. The surrounding α-Mg phase (known as “Al-rich α” or eutectic α) actually did not contain a high concentration of aluminum solid solution. Instead, the Al-rich α was composed of fine Al12Mg17β particles and Al-Mn-like particles (smaller than 0.5 μm) that were distributed in a low-Al-containing Mg matrix (∼4 wt pct Al). Such fine cathodic particles seem to participate strongly in the corrosion. Removing the primary β phase alone did not increase the corrosion resistance of the material, because many of the cathodic fine particles remained in the Al-rich α phase region. This work studied an HF-H2SO4/CaCO3 etching method for removing interdendritic phases (both the Al-rich α and the primary β) from the surface chill layer of the diecast thin plate. Therefore, testing in 5 wt pct chloride solution demonstrated that the Icorr of the HF-H2SO4/CaCO3-treated specimen was 3 to ∼16 μA/cm2, which was significantly lower than the Icorr ∼ 1600 μA/cm2 of the as-diecast Mg sample.

Interface conditions governing evaporation of stored liquids in presence of non-condensable gas

Experiments were conducted to determine the variation of interface temperatures during the storage and draining of liquid nitrogen from large containers in the presence of the non-condensable gas. A chilled layer was seen to be formed at the interface in the presence of the non-condensable gas and this layer advanced into the warm liquid at speeds higher than the characteristic speeds associated with thermal diffusion. A theoretical model was developed for the interface temperatures considering the evaporation from the stratified layer in the stored column of liquid. The predictions of the model were shown to compare well with the experimental measurements. A correlation was obtained for the interface temperatures when the proportion of the non-condensable gas was varied.

Continuous Semi-Solid Casting Process for Aluminum Alloy Billets

A new process for continuous semi-solid casting of billets of aluminum alloys was developed. Round aluminum alloy billets 75 mm and 150 mm in diameter are continuously cast in a semi-solid state by agitating the alloy in the agitating vessel with a mechanical screw and/or an electromagnetic stirrer. The solidification structure of the billets obtained by this process is a mixed structure of granular particles and a fine eutectic structure, except in a thin chill layer about 2 mm in thickness, which shows a dendrite structure. It was possible to use billets of AC4C alloy obtained by this process in the thixoforming process without surface conditioning.

Thermal erosion by laminar lava flows

Thermal erosion by hot lavas during their laminar flow over cold ground is investigated both theoretically and experimentally. An analysis of the steady forced convective heat transfer by a laminar channel flow at large Péclet numbers is presented, which is used to determine the final steady state erosion velocity as well as the thicknesses and timescales of the associated thermal boundary layers in both the lava and ground. The initial transient period involving the growth and remelting of a basal chill layer is also quantified. Laboratory experiments are described in which hot, molten wax flowed over and thermally eroded an underlying bed of solidified wax. The experimental observations of chill formation and thermal erosion are found to be in excellent agreement with the theoretical predictions. The theory is applied to predict rates of thermal erosion consistent with those observed in recent flows of basaltic lava in Hawaii and of carbonatite lava in Tanzania.

Breaking up two-layer cast-ion rolling-mill rolls with a chill layer

When the Magnitogorsk Metallurgical Combine began to make cast-iron rolls with a chill layer, it became necessary to break up the rolls after they had been removed from service. The rolls had to be divided into pieces no larger than 600 • 800 mm in order to be used as a component of the metallic charge for the production of alloyed cast iron in arc furnaces or induction furnaces. The combine conducted an experiment in which the rolls were broken up by two technologies already in use at the combine explosive fragmentation, with the blastholes for the explosive charges being perpendicular to the axis of the roll; breakup of the rolls on an impact breaker. The first method posed the danger of having fragments of the chill layer fly off as the blastholes were being drilled. In the second method, the body of the roll could not be broken up into pieces of the required dimensions, and the ball-weight of the impact breaker would itself be broken due to the high hardness of the body. Thus, two new technologies were proposed and tried out for breaking up two-layer cast-iron rolls explosive fragmentation in which the blastholes are located along the body of the roll; the use of an impact breaker after the roll body has been heated by a powerful mechanical cutter in the area where the roll is supposed to be divided. Explosive fragmentation with axial blastholes was chosen as the main technology after tests (two opposing blastholes are used). To perform a comparative analysis, nine rolls were broken up by the proposed fragmentation technology (A) and one was broken up by the existing technology (B). The results (in terms of one roll) are shown below:

リン酸塩系埋没材を用いた純チタン鋳造床 コーティング法による反応層の改善

It was attempted to coat the refractory models by zirconia to improve a reactive layer of the pure titanium denture base cast using phosphate-bonded investment and to compare with a usual investing method.When the coating refractory models were used, the small residual investment on the casting plate removing from the mold was observed.The surface hardness of the castings prepared with TAIVEST was hardly different between the two samples. However, the surface hardness of the castings prepared with T-INVEST C & B was slightly greater control samples on the casting surface to a depth of about 30μm, but there was little difference between the samples for the depth.In the coating samples, the microstructure of the surface of the castings showed almost no evident chill layer. The control samples had a chill layer and a columnar crystal layer extending from the surface toward the interior.Use of the electron probe microanalyzer (EPMA) to determine distribution of various elements in the superficial layer of casting plates showed the reactive layer contained Si and P in control samples. In coating samples, it showed a small reactive layer contained impure elements though there was a high density of Zr of the surface layer of the castings.The results are suggested that it is possible to improve a reactive layer of the surface of pure titanium denture base cast using phosphate-bonded investment by coating of the surface of the refractory models.