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A direct-chill (DC) casting simulation model was developed and applied to the authors' particle method simulation to enable three-dimensional thermo-fluid and solidification simulation of DC casting processing, including breakout. DC casting includes the feeding of molten alloy, changes in the direction and speed of molten alloy flow by a floating distributor, cooling of the alloy by the mold and water, state changes and solidification, and motion of an ingot relative to the mold by motion of a starter block. A salient difficulty that might arise with DC casting is breakout, which results from various factors related to these complex processes. The proposed simulation model enabled simulation of DC casting processes, including breakout, under simulation conditions that more closely resemble those of actual phenomena than do conventional methods (such as finite difference method and finite element method): starter block motion, ingot motion relative to the mold, and starter block – ingot interaction was addressed directly and naturally.

New 7xxx aluminum alloys with high alloying contents are being designed, which could induce serious hot tearing defects during direct-chill (DC) casting. Among all factors affecting hot tearing of 7xxx alloys, undoubtedly alloying elements play a significant role. In this study, the effect of main alloying elements (Zn, Mg, and Cu) on hot tearing of grain-refined Al-xZn-yMg-zCu alloys was investigated by a dedicated hot tearing rating apparatus simulating the DC-casting process. It was found that the minimum and maximum hot tearing susceptibilities occur for 4 to 6 and 9 wt pct Zn, respectively, indicating the complicated effect of Zn content. The hot tearing resistance of grain-refined Al-9Zn-yMg-zCu alloys is enhanced with increasing Mg content but is deteriorated with increasing Cu content. This can be attributed to the interaction of the thermal stresses, melt feeding, and final eutectics. The observed tendencies of the main alloying elements on hot tearing were also confirmed for four commercial 7xxx alloys. In addition, both the load value at non-equilibrium solidus and the SKK criterion proposed by Suyitno et al. using measured load developments were found to be good indicators in predicting hot tearing susceptibility. This study can provide a beneficial guide in designing 7xxx alloys considering the potential occurrence of hot cracks beforehand.

The sump profile during direct-chill (DC) casting provides critical information for understanding the solidification mechanism. In this work, the influence of the solid packing fraction (SPF) at the dendrite coherency point on the sump profile of DC and melt-conditioned direct-chill (MC-DC) casting is taken into account in the numerical model. It was found that the value of SPF has a significant influence on the sump profile, and that a constant value of SPF in the model cannot achieve a precise prediction of the sump profile in MC-DC casting simulation. Thus, a SPF as the function of grain size is proposed based on the data from the literature to improve the model. The results indicate that the improved model with the packing fraction function can predict a more accurate sump profile. The reason is the relationship between the grain feature and the SPF. In the model, the coarse dendritic grain structure is set as a low packing fraction value of about 0.3, but the fine globular grain structure is set as a high packing fraction value of about 0.6. The improved model has been verified by traditional DC casting and MC-DC casting of an AA6063 aluminum alloy.

Aluminum horizontal direct-chill casting (HDCC) faces challenges in achieving uniform solidification because of the non-uniform distribution of cooling water, leading to varying cooling rates at the top and bottom surfaces of the ingot. Here, hot cracking defects in HDCC are addressed using advanced simulation techniques. Using a three-dimensional finite element model, the impact of various casting parameters on hot cracking sensitivity (HCS) in aluminum billets was investigated. The model incorporates the energy equation, Navier-Stokes equation, and phase change theory to simulate the HDCC process, while the Magnin theory is applied to analyze hot cracking. Simulation results suggest that at a casting speed of 120 mm/min, a maximum HCS of 1.2 occurs at the billet center. This observation corresponds to experimental findings of hot cracking. However, reducing the casting speed to 80 mm/min significantly decreases the HCS to 0.59, effectively eliminating hot cracking in the billet. Additionally, the initial melt temperature minimally affects sump depth and mushy zone thickness, with only marginal changes in HCS observed. By optimizing the casting speed to 80 mm/min, defect-free aluminum billets were produced, confirmed by the absence of hot cracking in a cross-sectional examination of the billet.

Sedimentation of free-floating grains is the main origin of the negative centerline segregation in direct-chill casting of aluminum alloys. This study examines the motion and distribution of the floating grains during casting using experimental measurements and numerical modeling. The typical floating grains consisting of interior solute-lean coarse dendrites and periphery fine dendrites were experimentally observed only in the central region of the billet along with the negative segregation. The billet exhibits the strongest segregation at the center where the most floating grains are found. In simulations, under the action of the convection and the underlying forces, the grains floating in the transition region exhibit different motion behaviors, i.e., settling to the mushy zone, floating in the slurry zone, and moving upward to the liquid zone. However, most grains were transported to the central region of the billet and then were captured by the mushy zone and settled. Therefore, the floating grains comprise the largest share of the grain structure at the center of the billet, in agreement with the experimental results. Moreover, the simulation results indicate that the increased size of the grains promotes the sedimentation of the floating grains. These results are important for the future alleviation of negative centerline segregation in direct-chill casting of aluminum alloys.

For studying the changes of macro-physical field in the casting process of large-scale rare earth magnesium alloy, through the numerical simulation method, a two-dimensional axisymmetric multi-physical field coupling model was established by using the multi-physical simulation software COMSOL Multiphysics. The changes of temperature field, flow field, Lorentz force, and liquid fraction of large-size rare earth magnesium alloy with diameter of 750 mm under different electromagnetic parameters (magnetic field frequency and current intensity) in steady state of direct-chill (DC) casting were studied. The results reveal that using a magnetic field can reduce the temperature gradient and greatly accelerate the melt flow, the depth of the sump is reduced by about 50 mm. As the current intensity rises, the flow rate in the melt becomes accelerated, the sump depth becomes shallower, while the melt area with a liquid fraction of 0.5 to 0.63 increases. The Lorentz force rises as the magnetic field frequency increases, but the skin depth of the magnetic field decreases from 64.9 to 36.4 mm.

A comprehensive investigation, encompassing microstructural analysis of the subsurface and bulk regions, along with tensile testing near the solidus temperature in the range of 520–580 °C and with two strain rates (10 –4 and 10 –3  s −1 ), was conducted on two AA5182 alloy ingots (A and B) cast at casting speeds of 60 and 75 mm ∙ min −1 , respectively. Microstructural analysis revealed an equiaxed grain structure throughout Ingot A, whereas Ingot B transitioned from an equiaxed structure in the subsurface to a columnar grain structure in the bulk region. Regarding intermetallic phases, Ingot A showed predominant Al 6 (Fe,Mn), whereas Ingot B exhibited a high amount of needle-like Al 3 Fe. Consequently, Ingot A exhibited superior semisolid tensile properties compared to Ingot B at the given test temperatures. The difference between the two ingots became pronounced at the low strain rate of 10 –4  s −1 , with the brittle temperature range (BTR) values of Ingot B higher than those of Ingot A. An assessment of the hot-tearing susceptibility (HTS) using the BTR criterion revealed that the HTS of Ingot B was higher than that of Ingot A, confirmed by the occurrence of a large transverse macrocrack during the direct-chill casting of Ingot B.

The semisolid tensile properties of two AA6111 direct-chill cast alloys (A and B) have been studied. The Cu, Mn, and Si contents of alloy A are higher than those of alloy B. The microstructures of the alloys were analyzed before tensile testing and after tensile fracture. Isothermal holding was performed in the temperatures of 510, 520, 535, 552, 564 and 580 °C for 1 h to study porosity/void formation in both alloys. Tensile tests were conducted near the solidus temperature in the temperature range of 450–580 °C at a strain rate of 10–4 s−1. The strain during tensile testing was measured using the digital image correlation method to obtain reliable stress–strain curves. The results revealed that the tensile strengths of the alloys gradually decreased to zero with increasing temperature to arrive at the zero-stress temperature, whereas the strains at the failure decreased sharply with increasing temperature until zero-ductility temperature (ZDT) was reached. Moreover, the failure strain of alloy B at any given testing temperature was higher than that of alloy A. Non-mechanical and mechanical hot-tearing criteria were used to study the hot-tearing susceptibilities (HTSs) of the alloys. Considering the mechanical criterion, the ZDT and brittle temperature range of alloy A were lower and larger than those of alloy B, respectively, indicating that the HTS index of alloy A was higher than that of alloy B.

Abstract Horizontal direct chill (HDC) casting is one of the important manufacturing processes for producing aluminum billets. Because of its horizontal nature and gravity effects, controlling HDC casting still remains a challenge. In this study, we tried to simulate and optimize HDC casting to overcome these challenges. This process was investigated with a three-dimensional finite element model (FE) including energy, turbulent Navier–Stokes, and phase change equations applied to industrial HDC casting. The melt flow, sump profile, and mushy zone width were clearly identified under various conditions. The mushy zone width was strongly found to be a function of casting speed, and it was observed that increasing the casting speed increases the sump depth. The asymmetric sump shape has been found to be independent of the casting speed. The effect of water-cooling temperature on the sump depth and shape was not pronounced. The shape of the sump was strongly dependent on the melt inlet’s vertical position. The results revealed that gravity’s effect on the cooling water causes an asymmetrical sump shape that may affect the billet quality. It was found that the asymmetric sump profile problem can be solved by shifting the melt inlet’s vertical position downward. The findings from the simulation were correlated to actual industrial HCD casting, and a symmetric and uniform sump profile was successfully obtained.

A scalable ultrasound-assisted direct-chill casting technique was used to manufacture ultra-large 2219 Al alloy ingots (1250 mm in diameter; 2700 mm in net length). Following industrial ultrasonic casting experiments, three fundamental aspects of the resulting alloy were investigated: the microstructural refinement, the macro- and microsegregation mediation at different length scales, and the modification of eutectic skeletons and intermetallic compounds. This work presents new insights regarding the manufacture of ultra-large metallic ingots for special industrial applications.Graphical Abstract