Cast Shop Technology: DC Casting and Grain Refinement
Sponsored by: TMS Light Metals Division, TMS: Aluminum Committee
Program Organizers: Halldor Gudmundsson, Century - Nordural; Stephan Broek, Kensington Technology Inc

Tuesday 2:30 PM
March 21, 2023
Room: 31C
Location: SDCC

Session Chair: Philippe Khalil, HATCH


2:30 PM  
Recent Studies Using HR-TEM on the Fundamental Mechanism of Nucleation of α Aluminium on TiB2 in High Efficiency Grain Refiners: John Courtenay1; 1Mqp Limited
    Recent studies undertaken using HR-TEM (High Resolution Transmission Electron Microscopy) at BCAST, Brunel University London on the mechanism of nucleation of α aluminium on TiB2 in commercial high efficiency grain refiners has shown that efficiency as measured by the Opticast Nucleation test can be directly related to the extent to which the TiB2 particles have successfully formed a monoatomic layer of TiAl3 on their basal plane. This factor was found to be predominant over other factors generally considered to have an influence such as particle size distribution and average particle diameter in high efficiency grain refiners. As a result of this research it is now possible to produce a range of ultra high efficiency grain refiners which enable addition rates to be further reduced to levels as low as 0.15kg/t enabling the particle count to be significantly reduced benefiting liquid metal and as cast metal quality to be improved

2:55 PM  
A Cellular Automaton Model for Qualifying Current Grain Refiners and Prescribing Next-generation Grain Refiners for Aluminium Alloys: Georges Salloum-Abou-Jaoude1; Samah Sami1; Alain Jacot2; Luc Rougier2; 1Constellium C-TEC; 2ESI group
     In cast aluminium products, small equiaxed grains reduce the risk of hot tears and shrinkage porosities by facilitating the liquid feeding in the interdendritic liquid. Although grain refinement in aluminium alloys is well known and widely used, grain size control is still not always guaranteed industrially. This depends largely on the nature and fabrication quality of the grain refiner rod. In this work, we developed a cellular automaton model to establish a clear link between the grain refiner type/nature and grain refining efficiency while accounting for the principal physical phenomena affecting grain refiner performance: grain refiner nature, nucleant size distribution, recalescence, solute suppressed nucleation zone…At TMS2020 [1] we highlighted experimentally, the inconsistencies in grain refiner performance between different producers and in batches of the same producer. This model helps in qualifying grain refiners and would serve as a prescriber for designing next-generation grain refiners with superior efficiency.

3:20 PM  
Modelling Contactless Ultrasound Treatment in a DC Casting Launder: Christopher Beckwith1; Georgi Djambazov1; Dmitry Eskin2; Tungky Subroto3; Koulis Pericleous1; 1University of Greenwich; 2Brunel University; 3Constellium
    Ultrasonic processing can be performed without a vibrating probe by electromagnetic induction with a suitable frequency where resonance conditions can be established. This contactless method is suitable for high-temperature or reactive metal alloys providing purity of the melt and durability of the equipment. Hydrogen bubbles coming out of solution grow by rectified diffusion, and larger bubbles escape from the top surface leading to degassing. Violent collapses of the remaining smaller bubbles help grain refinement. In this presentation, application of a contactless 'top-coil' device to continuous casting via a launder is considered. Resonance is achieved by positioning of baffles on either side of the coil. Electromagnetic forces also cause strong stirring, increasing residence time. The process is modelled using time domain and frequency domain methods, and results for the proposed setup are compared with data obtained for the immersed sonotrode. Accuracy and sensitivity to process and model parameters is discussed.

3:45 PM  
Numerical Analysis of Channel-type Segregations in DC Casting Aluminum Slab: Keisuke Kamiya1; Takuya Yamamoto2; 1UACJ Corporation; 2Tohoku University
    In the direct chill casting of aluminum alloys, segregation of the solute concentration are formed in the slab. It has been observed the negative segregation in the center of the slab and stripe type segregation called channel segregation in middle of one. These segregations will be a cause of variation in the mechanical and chemical properties of the final product, therefore have to be controlled. But the mechanism of its formation is not clear, and the casting conditions under which the segregation is minimized have not been established. In this study, a numerical simulation model for segregation has been developed and the segregation distribution in the Al-Mg alloy slab was numerically analyzed. As a result, the segregation similar to that observed in actual slabs was reproduced on numerical analysis. This analysis showed that the channel-type segregation could be suppressed by colliding the strong down flow against to the solidification interface.

4:10 PM Break

4:25 PM  
Stability of SiC and Al2O3 Reinforcement Particles in Thermomechanical Processed Direct Chill Cast 6xxx Al MMnCs: Abdallah Abu Amara1; Guangyu Liu1; Dmitry Eskin1; Brian McKay1; 1Brunel University London
    Aluminium alloys reinforced by alumina (Al2O3) and silicon carbide (SiC) were investigated. Lab-scale DC cast billets with a diameter of 80 mm were cast by ultrasound-assisted stir-casting technology. The billets were subsequently thermo-mechanically processed. The distribution of particles in the matrix was analysed before and after thermomechanical processing. Hot rolling improved the distribution of reinforcement particles in the matrix. Reactions between the reinforcement particles and the matrix were investigated, and their implications studied. Alumina reinforcement reacted with magnesium (Mg) in the alloy to produce spinel and SiC oxidised producing a layer of silicon oxide (SiO2) around the particles. The consequences of these reactions are discussed. Whilst theoretical calculations of free energies for different carbides suggested that transition metals in the alloys should substitute the silicon in SiC, no reactions were observed in the physical experimentation, due to the weight percentages of the transition metals in the alloy being too small.