Aluminum Alloy Slab Research Articles

Digital simulation of aluminum alloy slab rolling with low relative reduction

It is noted that the traditional process for obtaining of aluminum alloys sheet metal is associated with semicontinuous casting of thick billets and their subsequent hot rolling. The first hot rolling pass is characterized by low reduction, which leads to strain localization in the surface layers of the metal. The finite element modeling of the first pass is performed and the stress-strain state is determined. It is found that the degree of deformation in the surface layer is approximately an order of magnitude higher than the value calculated through the total compression of the strip. At the center of the band, the deformations are practically equal to zero. Two zones along the length of the strip are revealed, in which the penetration depth of the deformation is additionally reduced. They are located at a distance from the ends of the strip, approximately equal to half of its thickness. The stress intensity is distributed quite uniformly over the thickness, but the average normal stress is distributed sharply unevenly over the thickness and is compressive near the surface and tensile in the center of the strip. This can provoke an increase in porosity, or the appearance of internal ruptures.

Characterizing mechanical change in metals using amplitude-modulated diffuse ultrasound

In this article, we present an ultrasonic method based on diffuse ultrasound with successive excitation amplitudes. This method provides amplitude-dependent parameters of diffuse ultrasound using coda wave interferometry, and these parameters can be used to characterize mechanical change in metallic materials. The localized mechanical change caused by an instantaneous 400°C thermal shock in a meter-scale aluminum alloy slab was characterized by measuring the diffuse-wave velocity change and decorrelation coefficient as functions of the excitation amplitude. The potential mechanisms and spatial distribution that cause the observed amplitude-dependent diffuse waveform modification are discussed. Combining the method presented here with complementary approaches will enhance the ability to nondestructively detect early-stage damage in the laboratory or in the field.

Implementation of a standard stream-upwind stabilization scheme in the element-free Galerkin based solution of advection-dominated heat transfer problems during solidification in direct chill casting processes

The present work has been conducted in order to propose an alternative solution for the heat transfer problem involved in direct-chill casting (DCC) processes, employing the element-free Galerkin (EFG) method. The internal energy balance has been solved on the basis of this global weak formulation under an Eulerian description. The EFG formulation has been adapted to a three-dimensional steady thermal problem on an aluminum alloy slab. Additionally, the advection dominated problem involved in the casting direction during the liquid-solid phase change has been stabilized by extending adequately the implementation of the stream upwind Petrov–Galerkin (SUPG) scheme to the EFG formulation. A detailed explanation concerning the suitable numerical procedure to achieve such an extension, has also been provided. The feasibility and reliability of this novel approach has been depicted by comparison with both finite element method (FEM) and finite volume method (FVM) based solutions. The results have demonstrated that a proper extension of the SUPG scheme to the EFG method allows the achievement of stable numerical solutions, when predicting the three-dimensional temperature distribution during the phase-change heat transfer phenomena involved in slab DCC processes.

Influence of Transport Mechanisms on Macrosegregation Formation in Direct Chill Cast Industrial Scale Aluminum Alloy Ingots

AbstractThe phenomena responsible for the formation of macrosegregations and grain structures during solidification are closely related. We present a model study of macrosegregation formation in an industrial sized (350 mm thick) direct chill (DC) cast aluminum alloy slab. The modeling of these phenomena in DC casting is a challenging problem mainly due to the size of the products, the variety of the phenomena to be accounted for, and the nonlinearities involved. We used a volume‐averaged two‐phase multiscale model that describes nucleation on grain refiner particles and grain growth, fully coupled with macroscopic transport: fluid flow driven by natural convection and shrinkage, transport of free‐floating equiaxed grains, heat transfer, and solute transport. The individual and combined roles of shrinkage, natural convection, and grain motion on the sump profile and macrosegregation formation are analyzed. The formation and evolution of grains are discussed. We show that it is important to account for all the named transport mechanisms to be able to explain the macrosegregation pattern observed experimentally in DC cast ingots.

Experimental and Numerical Study of the Influence of a Low-Frequency Electromagnetic Field on the As-Cast Structure of Horizontal Direct Chill Casting Aluminum Alloy Slab

The influences of low frequency electromagnetic field on the as-cast structure of horizontal direct chill casting aluminum alloy slab were experimental and numerical studied. The results of numerical analysis show that the interaction of the low-frequency electromagnetic field and the melt can generate an electromagnetically induced forced flow in the melt, which, in turn, changes flow pattern and temperature field in the mold. the as-cast structure of slab can be greatly improved by the changes of flow pattern and temperature field. The results of experimental analysis show that the grains of low frequency electromagnetic casting (LFEC) are fine, uniform, equiaxed, rosette-shaped; the surface of the slab of LFEC has no cold shut and less exudations. Moreover, the low-frequency electromagnetic field can improve the distribution of solute elements in the slab. The macrosegregation such as negative segregation and gravity segregation were reduced, which results in the homogenous distributions of the solute elements over the cross-section of the slab.

Analysis of solidification in Bridgman furnace as simulation of DC casting of aluminium alloy slabs

The vertical Bridgman directional solidification equipment has been used in several investigations to simulate direct chill casting of wrought aluminium alloys. As a basis for such investigations and alloy developments, it is important to have an understanding of the performance of the furnace used during simulation of the casting conditions. In this investigation the thermal conditions in the furnace have been analysed in detail, both by measurements and by mathematical modelling. The growth characteristics of the furnace, such as gradient, growth rates and cooling rates have been compared to conditions in large ingots. The direct chill casting conditions, which the simulations have been compared to, are casting of slabs of 330 and 600 mm thickness of an aluminium AA3003 type alloy. The results show that the experiments are able to simulate the cooling conditions in the ingots except from the surface zone. Comparisons of the microstructures have been made and a good agreement has been obtained for structure parameters such as grain size and DAS.

Numerical analysis of a viscoplastic problem with contact condition taking place in an aluminium casting

We consider a viscoplastic problem with contact condition modelling the thermomechanical deformations during casting of aluminium alloy slabs. We introduce a fictitious domain method to impose the metallostatic pressure on the thermal free boundary. Finally, we present some numerical results for a particular casting process during both the start and stationary stages.

Thermomechanical Effects in DC Casting of Aluminium Alloy: A Numerical Benchmark Study

The prediction of the ingot deformation during direct chill (DC) casting of aluminium alloy slabs would allow to optimise not only the casting recipe, especially during the critical starting phase, but also to design a mould geometry capable of producing flat rolling sheet ingots. Moreover. a good knowledge of the stress build up and of the strain rate field seems to be a prerequisite for the study of hot cracking, a really detrimental effect on productivity. In order to test the mathematical and numerical models now available in various codes. commercial and private packages, two benchmark tests aimed at modelling thermomechanical effects during the DC casting of aluminium alloys, have been carried out within the context of the Brite Euram research program EMPACT (European Modelling Project on Aluminium Casting Technology). The goal of this contribution is to present first the model definition of these two tests and next the main results obtained by the individual partners in the project with various numerical codes. In spite of a few discrepancies observed among the results, each model appeared to be capable of predicting quite accurately the main distortions undergone by an ingot during casting.

電磁鋳造法によるアルミニウム合金薄板スラブの製造

In order to improve the electromagnetic casting process for manufacturing thin slabs, the influence of bottom block on the electromagnetic field in the E.M. coil was investigated. Effects of the spout shapes and casting rate were also evaluated on outward appearance and structure of thin slabs. Furthermore, the thin 5052 aluminum alloy slab was cold-rolled to a final thickness reduction of 80% and the outward appearance and tensile properties of the rolled sheets was evaluated. Increase in the thickness of bottom block in the E.M. coil extremely decreases the E.M. pressure. Furthermore, a convex line is formed at the surface of the slab due to the flow of molten metal from the spout during the formation of meniscus. Therefore, a spout with cover is used in the fabrication of the slabs for the purpose of adjusting the meniscus thickness. A slab with a flat surface and 13 mm in thickness is obtained by using the spout with cover. When the fabricated thin slab of 5052 alloy is cold-rolled to a final thickness reduction of 80%, there is no surface defect, but edge cracks generate in the rolled sheet. The thin slab has tensile strength and elongation which satisfies the JIS requirements and is almost same tensile properties of the cold-rolled commercial DC hot plate.

Nondestructive testing of cracks in solid aluminum with a high temperature rf-SQUID

A hight temperature superconducting (HTS) rf-SQUID has been used in non-destructive testing (NDT). A two-hole HTS rf-SQUID is employed as a gradiometer sensor without using flux transformer coils. This gradiometer, maintained at liquid nitrogen temperature, is sensitive to enough to detect small cracks in an aluminum alloy slab covered by an 1″ thick solid aluminum alloy plate, yet it does not need any special magnetic shileding. This application of a HTS SQUID in NDT demostrates one of the important practical usage of high temperature superconductors. It also offers a possibility of solving simultaneously four NDT requirements: sensitivity, penetration depth, resolution, and portability of the device.

Centerline Segregation in Twin-Roll-Cast Aluminum Alloy Slab

Controlled twin-roll casting experiments were carried out with Al-Mg, Al-Fe, and other commercial aluminum alloys in order to investigate the effect of casting speed and alloy composition on the centerline segregation and cast structure. It is concluded that the centerline segregation increases as casting speed increases and alloy composition increases. The observations are discussed in terms of the interdendritic fluid motion through the partly solid regions, which arises because of the pressure gradient in the roll gap.