DC Casting Research Articles

Scalable DC casting of large-size AZ80 magnesium alloy slab under out-of-phase pulsed magnetic field: Experiment and simulation

The large-size AZ80 magnesium alloy slab was manufactured using direct chill casting assisted by out-of-phase pulsed magnetic field. Subsequently, the effects of OPMF on the as-cast structure and the Al content were investigated. By using numerical simulation, the macro physical fields including the flow field, the temperature distribution, and the sump profile were simulated and compared between the slab with and without OPMF. After introducing the OPMF, significant grain refinement occurred, and the macrosegregation degree of the Al element was alleviated. Compared with the case without OPMF, the simulations revealed that the melt flow rate and its range were greatly increased, accelerating the convective heat transfer in the sump. As a result, the temperature field was more uniformed distributed, the cooling rate was increased and the sump depth became shallower. The relevant mechanisms between the experimental results and the simulation results were discussed in detail.

The formation of three phases containing Fe and Mn in 5182 aluminum alloy

The categories, crystal types, morphology, dimension, distribution and selectivity of precipitation positions of alloy phases containing Fe and Mn in the DC casting ingot of 5182 aluminum alloy under industrial production conditions after being treated with different homogenization processes were studied through TEM and EPMA with FIB sample preparation. The formation process of three phases containing Fe and Mn was clarified as well. The results showed that there was only one category of alloy phase containing Fe and Mn in the as-cast 5182 aluminum alloy, which was one category of skeletal nonequilibrium constituent Al19(Fe,Mn)4′ with orthorhombic structure formed by the eutectic reaction L → α(Al)′ + Al19(Fe,Mn)4′. After the ingot was homogenized at a high temperature above 460 °C, there were three categories of alloy phases containing Fe and Mn, which were skeletal equilibrium phase Al19(Fe,Mn)4 with orthorhombic structure, short rod-like intermetallic phase Al3(Fe,Mn) with monoclinic structure and acicular alloy phase Al6(Fe,Mn) with orthorhombic structure, respectively. The metastable constituent Al19(Fe,Mn)4′ transformed into the equilibrium phase Al19(Fe,Mn)4 with orthorhombic structure and the alloy phase Al3(Fe,Mn) with monoclinic structure by desolation transformation Al19(Fe,Mn)4′ → Al19(Fe,Mn)4 + Al3(Fe,Mn). In addition, acicular alloy phase particles Al6(Fe,Mn) with orthorhombic structure were precipitated from the alloy matrix with supersaturated solute Fe and Mn atoms through the desolation reaction α(Al)′ → α(Al) + Al6(Fe,Mn). With increasing homogenization temperature, the skeletal constituent Al19(Fe,Mn)4 particles with orthorhombic structure were almost the same, and the short rod-like alloy phase Al3(Fe,Mn) particles, with monoclinic structure changed unobviously in morphology and size, but its number increased significantly. At the same time, the number and the size of acicular Al6(Fe,Mn) alloy phase particles with orthorhombic structure precipitated from the alloy matrix increased.

Microchemistry evolution during industrial DC casting and subsequent homogenization of aluminum alloy AlMn0.5Mg0.5 (AA 3105)

The properties of non-heat treatable Al wrought alloys are influenced by the materials microchemistry in terms of the portion of alloying elements either in solid solution or in precipitated form. In the present study we analyze the phase selection during solidification as well as the changes in solute level and particle state during subsequent homogenization of the Al-Mn alloy AA 3105 (ISO AlMn0.5Mg0.5). Characterization of the microchemistry reactions is performed by a combination of optical and scanning electron microscopy with differential scanning calorimetry and measurements of thermoelectric power as well as specific electrical resistivity. The results are underpinned by CALPHAD simulations of the second-phase particles in the as-cast state, while the changes in solute level as well as volume, size and type of second-phase particles during homogenization are tracked with a statistical microchemistry simulation tool named ClaNG. Owing to the high Si content of the present alloy the as-cast state is dominated by α-Al(Fe,Mn)Si phase constituent particles together with a few Al6(Mn,Fe) and Mg2Si phases. Homogenization is characterized by the formation and redissolution of Mg2Si and, at higher temperatures, dispersoids of the α-Al(Fe,Mn)Si phase.

Effect of chemical composition on the semisolid tensile properties and hot tearing susceptibility of AA6111 DC cast alloys

Effect of chemical composition on the semisolid tensile properties and hot tearing susceptibility of AA6111 DC cast alloys

Secondary Cooling Analysis of AZ80Y Magnesium Alloy Slab during DC Casting by Modelling and Verification Based on Experiment

The secondary cooling of AZ80 during DC casting was investigated by measuring the temperature at a given position during steady state. The experiment was carried out under different parameters including the water flow rate density (Q*) and initial temperature (Ti) of the impingement points. To theorize the heat transfer of the secondary cooling zone in practical DC casting, we designed a series of experimental equipment to simulate the secondary cooling with differing Ti (between 473 and 673 K) and Q* (between 20 and 100 L min−1 m−1) based on the DC casting temperature-measurement experiment above. Detailed analysis was carried out of both the experimental results combined with Q*. The empirical formulae of Rohsenow and Weckman were modified due to the need to divide the secondary cooling zone into an impingement zone and a free-falling zone. Finally, a verification of the model’s accuracy was conducted by comparing the results of the finite volume numerical simulation and the experiment, which revealed that the model exhibited extremely high accuracy.

Effects of Pulsed Magnetic Field Melt Treatment on Grain Refinement of Al-Si-Mg-Cu-Ni Alloy Direct-Chill Casting Billet

Al-Si-Mg-Cu-Ni alloy is widely used in the manufacture of high-performance car engine parts. Coarse, dendritic α-Al and large primary Si are common in Al-Si-Mg-Cu-Ni alloy DC casting billet, which is harmful to the performance of the final product. In this paper, a pulsed magnetic field melt treatment technique was applied to the melt in the launder of a DC casting platform to modify the α-Al and primary Si in the billet. A transient numerical model was established to analyze the electromagnetic field, flow field and temperature field in the melt during the pulsed magnetic field treatment. The effect of the magnetic energy on the clusters in the melt was analyzed. We found that during the pulsed magnetic field melt treatment, the number of clusters close to the critical size was increased due to the cluster formation work being reduced by the magnetic energy, which facilitated nucleation and refined the solidification structure. Furthermore, the flow velocity increased, and temperature homogenized in the melt during the pulsed magnetic field melt treatment, which benefitted the clusters close to the critical size distributed and maintained in the melt uniformly. The experimental results show that the α-Al and primary Si were small and homogeneous following the pulsed magnetic field melt treatment. The size of α-Al and primary Si was reduced by 25.6–44.4% and 32.2–54.1%, respectively, in the billet center compared to the conventional process.

Effect of electromagnetic parameters on melt flow and heat transfer of AZ80 Mg alloy during differential phase electromagnetic DC casting based on numerical simulation

Based on multi-physical field coupling numerical simulation method, magnetic field distribution, melt flow, and heat transfer behavior of a Φ300 mm AZ80 alloy billet during differential phase electromagnetic DC casting (DP-EMC) with different electromagnetic parameters were studied. The results demonstrate that the increase in current intensity only changes the magnitude but does not change the Lorentz force’s distribution characteristics. The maximum value of the Lorentz force increases linearly followed by an increase in current intensity. As the frequency increases, the Lorentz force’s r component remains constant, and the z component decreases slightly. The change in current intensity correlates with the melt oscillation and convection intensity positively, as well as the liquid sump temperature uniformity. It does not mean that the higher the electric current, the better the metallurgical quality of the billet. A lower frequency is beneficial to generate a more significant melt flow and velocity fluctuation, which is helpful to create a more uniform temperature field. Appropriate DP-EMC parameters for a Φ300 mm AZ80 Mg alloy are 10–20 Hz frequency and 80–100 A current intensity.

Numerical and Experimental Study on the Direct Chill Casting of Large-Scale AA2219 Billets via Annular Coupled Electromagnetic Field.

The internal coupled electromagnetic melt treatment (ICEMT) method is firstly proposed to produce high-quality and large-sized aluminum alloy billets. A three-dimensional model was established to describe the ICEMT process of direct chill casting (DC casting). The effect of ICEMT on the fluid flow patterns and temperature field in the DC casting of ϕ880 mm AA2219 billets is numerically analyzed. Moreover, the mechanisms of the ICEMT process on grain refinement and macrosegregation were discussed. The calculated results indicate that the electromagnetic field appears to be coupled circinate at the cross section of the melt, the fluid flow becomes unstable accompanied by the bias flow, and the temperature profiles are significantly more uniform. An experimental verification was conducted and the results prove that compared with traditional direct chill casting, the microstructures of the AA2219 large-scale billet under the ICEMT process are uniform and fine.

Investigation on Three-Dimensional Morphology of Channel-Type Macrosegregation in DC Cast Al-Mg Billets Through Numerical Simulation

Investigation on Three-Dimensional Morphology of Channel-Type Macrosegregation in DC Cast Al-Mg Billets Through Numerical Simulation

Effect of Internal Electromagnetic Stirrings DC Casting on Grain Refinement and Segregation of Large-Sized Billet of 2219 Alloy

An advanced method called internal electromagnetic stirring (I-EMS) was investigated to resolve the engineering problems like coarse-grain, inhomogeneous structure and macrosegregation. The electromagnetic stirrer functioned with internal-cooling was inserted in the melt during DC casting. In this study, a round billet of 2219 alloy DC cast with a diameter of 880mm under I-EMS process condition was produced, and its structure and composition distribution were comparatively characterized. The results show that the mean grain size decreased from the range of 872, 1023, 332 μm to the range of 317, 438, 271 μm at different billet positions with I-EMS. I-EMS consequently produce superior grain refinement and homogeneity. The effect of I-EMS on the grain-refinement and macrosegregation was also discussed.

Modelling of defects in aluminium cast products

Over the last 4 decades, remarkable progress has been made in the modelling of casting processes. The development of casting models is well reflected in the proceedings of the 15 Modelling of Casting, Welding and Advanced Solidification Processes (MCWASP) conferences that have been held since 1980.Computer simulations have enabled a better understanding of the physical phenomena involved during solidification. Modelling gives the opportunity to uncouple the physical processes. Furthermore, quantities that are difficult or impossible to measure experimentally can be calculated using computer simulations e.g. flow patterns and recalescence. However, when it comes to accurately predicting casting performance and in particular, the occurrence of defects like cracks, segregation and porosity there is certainly some way to go.In this paper, the current understanding of the main mechanisms of defect formation during shape and DC casting processes will be reviewed and requirements will be discussed to give a direction to making casting models more predictive and quantitative.

Microstructure and Mechanical Properties of DC Cast 7065 Aluminum Alloy

The microstructure and mechanical properties of 7065 alloy was investigate in this present work. The main intermetallic phases of the 7065 alloy identified by EDS analysis were (Mg,Cu) 2Zn, Al 2Cu and Al 7Cu 2Fe. The microstructure of the 7065 alloy after hot rolling mainly consists elongated fibrous grains containing sub-grains, indicating that dynamic recovery is the primarily mechanism during hot rolling. The 7065 alloy has lower quench-sensitive and higher mechanical properties than that of the 7050 alloy.

Research on causes of hot-tearing of AA3003 aluminum billet during DC casting process

AA3003 aluminum alloy made from raw scrap materials that have the advantage of economical use, but hottearing often occurs in the product billets of the direct chill casting process. This study used ANOVA analysis method for determination of chemical composition of AA3003 aluminum billet products to show influence of chemical composition on hot-tearing ability. The evaluation of the microstructure and chemical composition distribution of the elements by optical and scanning electron microscopes combined with energy dispersive spectroscopy showed the existence of impurities such as Cu, Zn, Fe, Pb exceeding the allowable limit in aluminum billets, especially at grain boundary, which can be the main reason for the hot-tearing of cast aluminum billets.

Flow Stress Behavior and Microstructural Evolution of DC Cast 7065 Aluminum Alloy During Hot Compression Deformation

The deformation behavior and microstructure evolution of DC cast 7065 aluminum alloy was investigated in the temperature range of 340-460 ℃ and strain rate range of 0.1-8 s-1. The flow stresses of the 7065 alloy are forceful function of deformation strain rate and temperature. The peak stress raises with reducing compression temperature, and at a designated deformation temperature, the peak stress increases with the increasing of strain rate. The hot deformation equation of the alloy is generated, and the deformation activation energy of the alloy is 117.869 kJ/mol. When the samples were deformed above 380℃, the α-aluminum dendrite in the initial microstructure was replaced by recrystallized grains, dynamic recrystallisation occurred during compression.

Development of processing maps for DC cast 7065 aluminum alloy

The deformation behavior and microstructure evolution of DC cast 7065 aluminum alloy was studied in the temperature range of 340-460 °C and strain rate range of 0.1-8 s-1. Processing maps were developed to evaluate the efficiency of the hot deformation and to identify the instability region. The results show that the optimum range of processing conditions are in the strain rate range of 0.01-0.1 s-1 and temperature range of 380-410 °C, where the efficiencies are much higher when compared to other regions. The peak efficiencies for the 7065 alloys is evaluated in the region of T=380-460 °C and ε=0.01-0.1 s-1. Recrystallized grain was observed under these deformation conditions. The dynamic softening is more pronounced at higher deformation strain rate and deformation temperature.

A Study on Hot Tearing in Direct Chill Casting of Al-Mn-Mg Alloys Using a Multi-scale Approach

A multi-scale approach for simulating hot tearing during the DC casting of aluminum alloys is presented. The novelty of this approach lies in the combination of a macro-scale finite element simulation of the DC casting process with direct prediction of hot tears via a meso-scale multi-physics granular model. This approach is capable of simulating hot tearing initiation, growth, and propagation within a representative volume element of the mushy zone. The change of cooling conditions experienced by the DC cast billet as a result of variations in casting speed as well as non-uniformity of heat extraction from different locations of the billet affect the deformation state, cooling rate, and thermal gradient, which further influence the strain rate, grain size, permeability, and feeding coefficient. Considering all the mentioned parameters, the multi-scale approach emphasizes the fact that hot tearing is a phenomenon resulting from the combination of the tensile deformation and restricted feeding of the mushy zone. The developed hot tearing formation maps identify the locations where hot tearing will occur as predicted by the multi-scale approach for two alloys—AA5182 and AA3104—thus demonstrating the approach’s sensitivity to both processing parameters and alloy composition.

Influence of ultrasound irradiation on transient solidification characteristics in DC casting process: Numerical simulation and experimental verification

It is well known that solidification of molten metals occurs under the influence of transient unsteady phenomena, which are difficult to control in actual casting operation. Examples include buoyancy flows, natural heat convection, repeated remelting and solidification in mushy zone and solid shell at the mold interface. This paper presents the results suggesting that ultrasound waves, irradiated into the hot-top mold offers an attractive way to control the transient phenomena in DC casting of aluminum alloy billets. A novel mathematical model was developed to simulate the DC casting with considering transient melt flow, heat transfer, ultrasound propagation, acoustic streaming and solidification. It was found that ultrasound irradiation alters the solidification behavior of melt and sump evolution especially in the earlier stage of casting, however as the billet length increases, the sump profile becomes almost the same for both the ultrasonic and conventional castings. In this condition, the casting speed becomes the key parameter influencing the sump evolution and mushy zone volume. The results reveal that ultrasound-driven acoustic streaming and turbulent oscillations result in a suppression of buoyancy flow in the sump and lead to an increase of frequency of the melt temperature oscillations at the solidification interface. One of the useful results of these phenomena can be a more frequent repetition of remelting/solidification cycle and improvement of the billet quality, particularly the billet surface morphology. The effect of ultrasound irradiation on the billet morphology was verified experimentally using a pilot DC caster.

Effect of Combined Electromagnetic Fields on Microstructure and Properties of Large-Sized Ingot of 2219 Aluminum Alloy

Large-sized 2219 aluminum alloy ingot has wide application prospect in aerospace and military fields. Severe defects, such as coarse grain, the inhomogeneity of structure and macrosegregation occurred in large-sized aluminum ingot produced by normal DC casting. The application of a single magnetic field in DC casting process cannot solve these defects. In this paper, a new method with the combination of electromagnetic fields imposed on bulk melt treatment during DC casting was proposed. And a φ508 mm ingot of 2219 aluminum alloy was prepared in this method. Compared with the normal DC casting, the effect of the combined electromagnetic fields on the microstructure and properties was studied. The experimental results demonstrate that the application of the combined electromagnetic fields significantly refines the grains, and the grain size distribution on the cross section of the ingot tends to be more uniform as well as the mechanical properties are significantly improved. The microstructure and grain size distribution can be significantly affected by different combined electromagnetic fields. It is considered that the appropriate combined electromagnetic fields parameters play an important role in controlling the homogeneity of large-sized ingots.

Effect of Cu Content on Ageing Behavior for AA3104-H19 Can Body Sheet

AA3104 ingots with different Cu content (0.1wt.%, 0.2wt.% and 0.3wt.%) were prepared by DC casting, and then the ingots were processed to 0.26mm sheets with the method of making AA3104 can be body sheet. The AA3104-H19 sheets were aged at 180°C and the aging strengthen effect were found in the 0.2wt.%Cu and 0.3wt.%Cu alloys. Optical micrograph (OM), X-ray diffraction, high resolution transmission electron microscope were used on the sheets after different ageing time. Rod like coherency precipitates with the length about 5-10nm and the thickness about 2-3nm which were parallel to the [111] plane of the matrix was precipitated at peak aging (180°C-2h). According to the result of the thermodynamic phase diagram calculation, the precipitates should be S-Al2CuMg phase, but the structure of the precipitates were different from the precipitates reported in 2XXX alloy.

Modelling macrosegregation modification in dc casting of aluminium alloys in sheet ingots accounting for inlet melt flow, equiaxed grain morphology and transport

Macrosegregation is a severe defect present in direct-chill (DC) cast aluminium ingots and billets. In the recent years, experimental studies were conducted to modify and to an extent optimize macrosegregation formation by modifying the inlet melt flow. Due to several limitations, the grain settling behavior and corresponding liquid flow pattern is difficult to analyze using experiments. Simulations on the other hand can provide this insight. However, conducting 2D sheet ingot simulations, as has been previously done, provides an incomplete description of flow pattern. To avoid this and as a first qualitative study, full scale 3D sheet ingot simulation results with two different inlets are presented in this paper. A simplified three-phase multiscale solidification model accounting for solidification shrinkage, natural convection and equiaxed grain growth and transport is used to conduct this study. We show that modification of inlet flow results in modification of grain settling and eventually leading to modification of macrosegregation. The impact of grain morphology is also additionally analyzed.