Horizontal Direct Chill Research Articles

Effect of substrate microstructure on corrosion resistance of cast and forged anodised 6082 Al alloy

This work addresses the effect of the surface morphology of a 6082-aluminium alloy on the characteristics of the anodic layer generated by an anodising process using two current densities. The samples tested were horizontal direct chill (HDC), vertical direct chill (VDC) cast billets, and the same material after forged + T6 ageing treatment. Samples were anodised in a mixed citric acid‑sulphuric acid electrolyte using 0.5 A⋅dm−2 and 1.5 A⋅dm−2. D.C. current densities. The protective character of the oxide layer was studied by electrochemical impedance spectroscopy (EIS) in 0.1 M NaCl solution.Microstructural characterisation revealed that the microsegregation and forging processes have a significant effect on the growth of the oxide layer as well as on the optimum anodising conditions. The EIS study showed that the corrosion protection provided by the oxide layer on Al6082 alloy was strongly affected by the manufacturing process, with thinner oxide layers obtained for cast billets. Heat treatment and forging homogenise the microstructure, which positively affects anodising and modifies the growth rate and thickness of the oxide layer. This effect makes obtaining a thicker oxide layer with good corrosion protective properties possible by using lower current densities for forged samples.

Analysis of the Quality of Incoming AlSi9Mn Alloy Ingots

Previous research revealed that the quality of the ingots produced by different primary or secondary alloy suppliers can differ remarkably. In this way, the quality of the liquid metal and the castings produced from it can be affected by the impurity content of the ingots used as charge material. In this work, a modified reduced pressure test (RPT) technique, which is based on the remelting of samples extracted from ingots, was applied to investigate the quality of primary AlSi9Mn ingots made by horizontal direct-chill (HDC) casting and gravity casting techniques. For the evaluation of metal quality, image analysis of the cross sections was applied. Pore area fraction, number density, normalized bifilm index, and normalized total pore perimeter were determined, and the relationships between the different metrics were analyzed. The results were compared with the melt quality assessment of the as-melted batches made from the ingots. Solidification simulations, thermal analysis, and microstructural investigations were conducted to investigate the solidification conditions of traditional and remelted RPT samples. Based on the results, the HDC cast ingots possess lower oxide and gas concentrations, which can be traced back to the differences in the melt preparation and casting technologies of the ingots. The comparison of the parameters evaluated by image analysis revealed that there is a strong linear relationship between normalized bifilm index and normalized total pore perimeter. The possible sources of error in ingot quality evaluation are highlighted.

Prediction of Limiting Casting Speed in a Horizontal Direct-Chill Casting through Numerical Modeling and Simulation

Limiting casting expression speed was obtained and the flow redistribution and thermal history in a horizontal direct-chill (HDC) casting was predicted using the numerical modeling approach. The governing solidification equations were non-dimensionalized to understand the relevant contribution of each term in the solidification processes in the HDC system. The effect of an increase in the casting speed on the flow characteristics and sump length was represented by the Péclet number Pe. Details of the simulation reveal that at a low Pe, the natural convective flow creates minor counter-clockwise recirculating cells in the lower half of the HDC domain. However, at a Pe above 82.75, the minor recirculating cells disappear due to the strong forced convective flow from the upstream. Additionally, an increase in the Pe increases the sump length, strength, and spread of the turbulence field within and beyond the mold region. The limiting casting conditions are computed by predicting the sump length over which the alloy temperature is above the solidus temperature. This gives a simple relation for the casting speed as a function of the geometrical data and the alloy properties. The current work is useful to casting engineers who always rely on trial and error in choosing a new casting speed whenever a new alloy is to be produced. Hence, with the new information and the casting speed relations, it is possible and easy to predict the operating window over which melt break-out can occur during HDC.

Modeling and optimization of industrial-scale horizontal direct chill casting

Modeling and optimization of industrial-scale horizontal direct chill casting

Flow Redistribution and Thermal Computation in a Horizontal Direct-Chill Casting of Aluminum-Copper Binary Alloy System

Flow Redistribution and Thermal Computation in a Horizontal Direct-Chill Casting of Aluminum-Copper Binary Alloy System

Influence of various aspects of low-Reynolds number turbulence models on predicting flow characteristics and transport variables in a horizontal direct-chill casting

Computational Fluid Dynamics (CFD) was used to simulate the solidification in a horizontal direct-chill (HDC) casting using five low-Re k-ɛ turbulence model: including the v2¯−f model of Durbin (V2F), Yang-Shih (YS), Chang-Hsieh-Chen (CHC), Abid (AB), and Abe-Kondoh-Nagano (AKN). The model incorporated turbulence energy production due to buoyancy in the k and ɛ equations to predict flow pattern, eddy viscosity ratio, turbulence intensity, turbulence velocity, turbulence energy production due to buoyancy, solid fraction, and temperature. Three sets of grids were systematically chosen in such a way that the grid refinement factor was above 1.3. The results obtained indicate that the solution was independent of grid size. The flow pattern predicted using the turbulence models are generally similar, but the V2F indicated additional minor counter-clockwise recirculating cells toward the bottom mold. Further, the solutions indicate that turbulence energy production due to buoyancy contributes to the strong turbulence levels predicted towards the top mold region. The predicted velocity of the mean flow for the V2F model in the flow domain is higher, followed by the YS model and least for the CHC, AB, and AKN models. The eddy viscosity ratio is highest with a value of 144 at y+<100 for the CHC model, followed by AKN and AB with eddy viscosity ratios of 144 and 137 respectively. Then, the YS has a maximum eddy viscosity ratio of 114 at y+<50, V2F has the least maximum eddy viscosity ratio of 78 at y+<150. The turbulence intensity, the turbulence velocity, and the turbulence energy production due to buoyancy were highest towards the top mold for the CHC, AB, and AKN than the YS and V2F models. The V2F and YS predicted lower temperature curves and higher solid fraction curves towards the mid-section of the profiles than the CHC, AB, and AKN models.

Study on the transitional structures of 7075 aluminum alloy ingot after switching off a low-frequency electromagnetic field in the horizontal direct chill casting

The transitional structures of 7075 aluminum alloy ingot after switching off a low-frequency electromagnetic field (LFEF) in the horizontal direct chill casting was investigated. The results showed that the equiaxed grains with the LFEF are firstly transformed to columnar grains and then to feathery grains without the LFEF. Also, there exists a transitional region consisting of relatively fine equiaxed grains between the equiaxed grains and the columnar grains. Crystallographic analysis indicated that only the relatively fine equiaxed grains with ideal orientations can grow into columnar grains. Moreover, there exist multiple twin relationships between some adjacent feathery grains, which have a near-common or common 〈110〉 direction. The equiaxed grains with the LFEF result from the forced convection. The relatively fine equiaxed grains and the columnar grains are attributed to the weakening of the forced convection when the LFEF is switched off. For the feathery grains, it is of interest to find that the quasicrystal-enhanced nucleation mechanism is responsible for their formation under high thermal gradient although it has been reported for twinned equiaxed grains under nearly nil thermal gradient in the literature.

Influence of Fe and Si Addition on the Properties and Structure Conductivity Aluminium

AbstractThe effect of iron and silicon addition on the structure and properties of aluminium wire rod obtained in the laboratory horizontal direct chill casting process has been analysed. In addition, the impact of laboratory wire drawing process has been examined. The addition of iron and velocity of casting increase the strength of aluminium wire rod in as-cast condition while the electrical conductivity drop acceptable. Moreover, the laboratory wire drawing process causes work-hardening wires and increase drawing tension as a result of fragmentation of structure and growth of grain boundaries. It has been shown that iron is beneficial for mechanical and technological properties of aluminium.

Potential of horizontal direct chill cast EN AW 6082 rods as forging stock in the manufacture of light weight suspension components

Commercial EN AW 6082 rods cast at less than 50 mm in diameter via horizontal casting appear to be adequate candidate as forging stock for the manufacture of small size automotive suspension components. Cast forging stock relies entirely on the forging deformation to develop the fibering known to be very beneficial for superior dynamic and impact properties. Hence, the forging die design is critical to ensure the sufficient amount and suitable orientation of fibering across the section of the component. Forgings produced from cast stock, submitted to an artificial ageing cycle directly after the forging step offer superior fatigue and impact energy values with respect to their counterparts processed with a solution heat treatment (SHT). The superior fatigue and impact energy values of the former are attributed to the particle characteristics; i.e. the spacing of void forming particles in these forgings is relatively smaller than in forgings processed with a separate SHT. The coalescence of voids at these particles eventually occurs at smaller loads and deteriorates toughness.

Influence of Casting Velocity on Structure and Properties of AlFe0,5 Alloy

The effect of iron addition on the structure and properties of aluminium wire rod obtained in the laboratory horizontal direct chill casting process has been analyzed. In addition, the impact of the casting speed on the properties of aluminium bars, containing the 0.5 wt% of Fe, and laboratory wire drawing process has been examined. The addition of iron increase the strength and plasticity of aluminium wire rod in as-cast condition and after wire drawing process, while the electrical conductivity drop acceptable. Moreover, by improving the plasticity of wires became possible to increase the deformability limit, measured by the reduction in the wire diameter by drawing to a level of less than 0.5 mm. Small-diameter wires are used for the construction of automotive wire harnesses, cables battery or winding wires. It has been shown that iron is beneficial for mechanical and technological properties of aluminium, and the horizontal direct chill casting process by graphite crystallizer may be an alternative solution in comparison with industrial scale of continuous casting and rolling by Properzi method (CCR) or Southwire SCR process in the context of the preparation of smaller amounts of material with scrap metals.

Structural and crystallographic study on 3004 aluminum alloy ingot by horizontal direct chill casting under combined electromagnetic fields

Abstract

A New Approach of Casting Aluminium Alloy Bar by Applying Low Frequency Electromagnetic Field

Aluminum is the richest metallic element in the earth, the ingots cast by DC casting process are usually extruded into aluminum bars. When the final products do not require high strength, this process appears to be low efficiency and high cost. We try to design a new technology to cast aluminum bar by horizontal direct chill (HDC) casting process directly. An electromagnetic field is applied during the horizontal continuous casting of 6061 aluminium bar with a diameter of 30mm. The experimental results show the asymmetry of the sump can be overcome by electromagnetic field. Ingot with good upper and lower surface quality is obtained. The structure of ingot is refined and the angle between growth direction and horizontal direction becomes small with increasing casting speed.

Comparison of Cast and Extruded Stock for the Forging of AA6082 Alloy Suspension Parts

High-precision near-net shape parts with excellent surface qualities can be produced with the forging process with a minimum of finishing operations thanks to the good formability of aluminium alloys. There has been a rapid increase in the use of aluminium forgings predominantly in the automotive industry, where weight savings for reduced fuel consumption and exhaust emissions is mandated by legislation. Aluminium forgings provide, in addition to low weight, high strength, good corrosion resistance and a fibrous grain structure to improve fatigue resistance. Typical commercial forging stock is the round bars produced by the extrusion of cast billets. An alternative process route that has received increasing attention in recent years is the casting of forging stock by a horizontal direct chill casting technique to make smaller billets without the need for extrusion to reduce their diameter. The anisotropy imparted to the forging stock via extrusion, often regarded as useful for the forging, is certainly missing in the former. However, cast stock has been reported to be more resistant to the formation of coarse surface grains than the extruded counterpart. The present work was undertaken to compare the casting and extrusion routes for the manufacture of 6082 alloy forging stock.

Effect of low frequency electromagnetic field on as casting structure and surface quality of horizontal direct chill casting 7075 alloy

Horizontal direct chill (HDC) casting is a well established production route for aluminium alloy ingots; however, the ingots may suffer from inhomogeneous microstructures and serious macrosegregation due to the unbalanced cooling condition and gravitational effect. The present study considers the HDC casting of 7075 aluminium alloy ingot under the influence of a low frequency electromagnetic field (LFEF). Temperature measurement is employed to analyse the effect of LFEF on the HDC casting process. Surface topography and structure observation are conducted to analyse the effect of LFEF on the surface and interior quality of the HDC ingot. The results show that the LFEF can effectively uniformalise the thermal distribution, flatten the sump shape, improve the ingot surface quality, promote a transition from columnar/feathery to equiaxed dendritic growth and has a distinct grain refining effect.

Macrosegregation in horizontal direct chill casting of ternary Al alloys: Investigation of solid motion

Macrosegregation in direct chill casting processes is controlled by fluid flow due to the thermosolutal natural and forced convection, shrinkage, and transport of unattached solid grains. Because grain refinement is usually used in aluminum direct chill casting, some effort must be made to model free-floating solid grains, and their attachment to a rigid mushy zone. Criteria for attachment vary, but many are based on using a critical solid packing fraction, which is treated as uniform and constant throughout the domain. In the case of horizontal casting (HDC), gravity acts perpendicularly to the casting direction, and the assumption of a uniform packing fraction cannot be applied because the solid particles attach to some surfaces by settling and others by being swept into the rigid solid from below. In this simulation of HDC casting of an Al-Cu-Mg alloy, the rigid and unattached solid is tracked separately, and a rule set is developed to determine the attachment of free-floating solid. Comparison between cases with and without unattached solid movement shows qualitatively different results, particularly in bottom part of slab. Non-uniform packing fractions cause very different segregation patterns in the lower half of the ingot compared to the cases with no solid movement, less segregation near centerline compared to uniform packing fraction cases, and positive segregation near the place where inlet jet impinges on the mushy zone.

Effect of casting speed on surface quality of horizontal direct chill casting 7075 aluminum alloy ingot

7075 aluminum alloy ingot with the diameter of 100 mm has been produced by horizontal direct chill casting in difierent casting speed. The efiect of the casting speed on the ingot surface and subsurface layer was studied by surface observation and subsurface structure analysis. It was found that increasing the casting speed results in the adding of segregation knots in the ingot surface. The thickness of the dendrite microstructure layer in the subsurface reduces with increasing the casting speed. And the elements of Zn, Cu and Mg enrich in the coarse dendrite microstructure layer of the ingot. KEY WORDS Horizontal direct chill casting; Casting speed; 7075 aluminum alloy; Surface quality

Floating Grains in the HDC Casting 7075 Aluminum Alloy Ingot

7075 aluminum alloy ingot with the diameters of 100 mm was produced by Horizontal Direct-Chill (HDC). The temperature in the melt was measured and the ingots were examined in detail with the aim to reveal the floating grains in the HDC ingot. Experimental results show that very large floating grains with coarse dendrite arm spacing (DAS) mainly concentrate in the half-moon area near bottom surface of the HDC casting ingot, under the function of gravity. The floating grains in the HDC casting process is much bigger than that founded in Vertical Direct-Chill (VDC) casting process.

The Effect of Casting Speed on Sump Shape and Ingot Surface of HDC Casting 7075 Aluminum Alloy Ingot

7075 aluminum alloy ingot with the diameter of 100 mm has been produced by horizontal direct chill casting in different casting speed. The effect of casting speed on the sump profile and the ingot surface quality was studied by sump profile observation. It was found that increasing the casting speed results in the deepening of the liquid pool, the adding of segregation knots and the reducing of cold shouts in the ingot surface. It is also found that the depth of the liquid pool is directly proportional to the casting speed and the squared radius of the ingot.

DC casting of light alloys under magnetic fields

The working principle of LFEC(Low frequency electromagnetic casting) process developed in Northeastern University, China was introduced and the metallurgical results of LFEC were discussed according to the casting practices. The low frequency field around the mold produces Lorenz force, which can be divided into two parts: one is the potential force which will be balanced by a pressure gradient of the liquid and results in the formation of a convex surface meniscus and improves the surface quality; the other is the rotary force which stirs the liquid in the mold to refine the microstructures and homogenize the distribution of alloying elements. LFEC can refine microstructures remarkably, improve surface quality of the ingots, depress macrosegregation and eliminate cracks. Some new technologies, such as horizontal direct chill casting under low-frequency electromagnetic field (HLEC), DC casting of hollow billets under electromagnetic fields (HBEC), electromagnetic modifying of hypereutectic Al-Si alloys(EMM), air film casting under static magnetic field (AFCM), and multi-ingots casting under low-frequency magnetic field (MLFEC) were developed based on LFEC.

Effect of Electromagnetic Field on Horizontal Direct Chill Casting of 7075 Aluminum Alloy

The influence of different electromagnetic fields on the horizontal direct chill (HDC) casting of aluminum alloy is studied. 7075 aluminum alloy with 100-mm in diameter is produced by HDC casting process; single electromagnetic field located before or around the mold and an out-phase electromagnetic field (OPEMF) are applied in the HDC casting process. The effect of different electromagnetic fields on the HDC casting solidification behavior and as-cast structure is investigated. The electromagnetic field can effectively make uniform thermal distribution in the molten pool and refine the as-cast structure. The OPEMF is more efficient than the single electromagnetic field in improving the as-cast structure of HDC cast ingots.