Cast Shop Technology: DC Casting
Sponsored by: TMS Light Metals Division, TMS: Aluminum Committee
Program Organizers: Samuel Wagstaff, Oculatus Consulting

Thursday 8:30 AM
March 18, 2021
Room: RM 29
Location: TMS2021 Virtual

Session Chair: Philippe Jarry, Constellium; Samuel Wagstaff, Oculatus


8:30 AM  
Simulation-based Analysis for Optimization of Casting Process in AA7075: Siamak Rafiezadeh1; Philip Pucher1; Steffen Neubert1; Waldemar Ivanov1; 1AMAG
    The stability of the Aluminium DC casting process is dependent on tight control of a multitude of parameters. Even slight fluctuations within the defined production process window of crack sensitive wrought aluminum alloys are potentially detrimental. However, for certain parameters the extent to which their variance can be reduced is severely limited. For that reason, the continuous casting process for AA-7075 rolling slabs is modelled using MAGMA CC. Model assumptions are validated experimentally in an industrial DC casting pit. Different mold and cooling conditions as well as casting temperatures are simulated and their effect on the stress distribution in the slab is investigated. Criteria are developed to assess the tendency towards casting defects, such as center cracks due to process parameter fluctuation. The findings are used to identify potential for process optimization.

8:50 AM  
Characterization of Ingots Cast with the APEX™ Casting System: Craig Cordill1; Gerhard Castro1; Bin Zhang1; 1Wagstaff
    Traditional aluminum direct-chill rolling ingot casting uses a fixed mold bore opening (MBO) that is optimized to cast an ingot that is flat in the steady state region under particular conditions. A fixed MBO mold is chosen as a compromise between cast speed and amount of ingot butt swell. The APEX Casting System has controllable rolling faces that allows the MBO to change dynamically during casting. The mold can optimize the final shape of the ingot at a wide range of casting parameters from cast start to end. This removes the traditional limits on speed with a fixed MBO. With the ability to cast faster and increase pit productivity, internal metallurgical properties such as macrosegregation and porosity can become the limiting factor for speed. Comparisons of metallurgical data from ingots cast at different speeds up to 120mm/min with the APEX Casting System will be discussed and compared to other technologies.

9:10 AM  
Effect of Ultrasonic Melt Treatment on the Sump Profile and Microstructure of a Direct-chill Cast AA6008 Aluminum Alloy: Tungky Subroto1; Gerard Serge Bruno Lebon1; Dmitry Eskin1; Ivan Skalicky2; Dan Roberts2; Iakovos Tzanakis3; Koulis Pericleous4; 1Brunel University London; 2Constellium UTC; 3Oxford Brookes University; 4University of Greenwich
    This work focuses on the effects of ultrasonic melt treatment (UST) during direct-chill (DC) casting on the temperature distribution across the billet, sump profile and the resulting microstructure. Two AA6008 billets were cast; one was treated with UST in the hot top while the other was not. To determine the temperature distribution along the billet, multi-point temperature measurements were made across the radii of both billets. The sump profile was also analyzed through macrostructure analysis, after Zn was poured into the sump, while structure refinement was quantified through grain-size measurements. A numerical model of ultrasound-assisted DC casting is validated using the temperature measurements. As an outcome, this study provides information on the extent to which UST affects the sump profile and the corresponding changes in the microstructure. The knowledge gained from this study paves the way towards optimization of UST parameters in DC casting.

9:30 AM  
The Influence of the Casting Speed in Horizontal Continuous Casting of Aluminium Alloy EN AW 6082: Akin Obali1; Kerem Dilek1; Mertol Gokelma2; Seracettin Akdi3; Deniz Kavrar Ürk1; 1Sistem Teknik Industrial Furnaces Ltd.; 2Izmir Institute of Technology; 3Akdi Engineering and Consultancy
    Vertical direct chill (VDC) casting is commonly used to produce slabs and billets from wrought aluminium alloys. The facts that the VDC is not a continuous process and moulds must be prepared for the next batch decrease the productivity of the process. Alternatively, horizontal direct chill (HDC) casting simplifies the process and allows for continuous casting. The casting speed in VDC casting process is easier to control and can be optimised for different alloys. This study focuses on the effects of casting speed on the macro structure of 6082 aluminium billets with 60 mm of diameter. A demo-scale unit was used for the trials and the casting speed was changed from 310 to 385 mm/min. Changes in the surface condition, macro cracks, and the diameter of the billets were investigated. The effect was clearly observed, and macro failures were detected for casting over 355 mm/min.

9:50 AM  
The Impact of Casting Conditions on Edge Cracking of AA5182 Ingots during Hot Rolling: Samuel Wagstaff1; 1Oculatus
    The hot rolling of large ingots is the predominant process for producing plate, sheet, and foil. During the hot rolling of aluminum-magnesium alloys, edge cracking tends to dramatically increase with increasing magnesium concentration often resulting in significant unplanned scrap generation. It has been observed that significant cracking most frequently occurs in the start-up region of the ingot, which prompted the current investigation into the impact of casting conditions on edge cracking. By taking samples from the start-up and steady-state regions of AA5182 ingots and subjecting them to different simulated preheat rates, we were able to observe a noticeable difference in liquation and void formation behavior on the ingot surface. For a given casting condition, there appears to be a threshold preheat rate beyond which significant void formation occurs. Our investigation indicates that the start-up region of DC cast ingots has a lower threshold temperature, thus leading to increased edge cracking.

10:10 AM  
Reducing Gas Shrinkage Porosity in AlMg Alloy Slabs: Igor Kostin1; Aleksandr Sidorov1; Aleksey Startsev1; Andrey Krechetov1; Aleksandr Krokhin1; Sergey Belyaev2; 1UC RUSAL; 2SFU
     Reducing gas-shrink porosity is a topical issue in the production of large slabs made of aluminum-magnesium alloys by direct chill casting. To do this, various methods of influencing the melt are used, both during the preparation and during the crystallization of slabs. Currently, due to the growing demand for slabs of large cross-sections for rolling and cutting and stricter requirements for final products, research on reducing porosity is widely used in the industry.The paper presents data obtained from the study of porosity in slabs of aluminum-magnesium alloys produced by direct chill casting at the Pilot casting complex (PCC) of the company OK RUSAL. The dependences of porosity morphology on the alloy composition, size and technological parameters of casting are presented. The main causes of porosity are considered, and metallographic images of the distribution of pores along the slab cross-section are presented.

10:30 AM  
Molecular Dynamics Simulations of the Evolution of Residual Stresses during Rapid Solidification of Aluminium: Michail Papanikolaou1; Konstantinos Salonitis1; Mark Jolly1; 1Cranfield University
    It is well known that residual stresses are quite common in castings and they emerge due to uneven cooling conditions. Nowadays, the development of atomistic modelling techniques has allowed for the in-depth investigation of the solidification process mechanics as well as the distribution of residual stresses. In this study we have performed Molecular Dynamics simulations to investigate the evolution of residual stresses during homogeneous nucleation in pure Aluminium and their distribution over the simulation domain. A simulation box containing a large number of Aluminium atoms has been heated up and subsequently quenched under various cooling rates. The potential and kinetic energy as well as the evolution of various atom types (Face-Centred Cubic, Amorphous and Hexagonal Close Packed) has been monitored during the melting and quenching stages. The obtained results suggest that the cooling rate significantly affects the distribution and the final magnitude of residual stresses in the simulation domain.

10:50 AM Question and Answer/Panel Discussion