Cast Shop Technology: Grain Refining and Solidification
Sponsored by: TMS Light Metals Division, TMS: Aluminum Committee
Program Organizers: David Gildemeister, Arconic Technology Center
Wednesday 2:00 PM
March 1, 2017
Location: San Diego Convention Ctr
Session Chair: Stephen Instone, Hydro Aluminium Rolled Products GmbH
2:00 PM Introductory Comments
Effect of Ultrasonic Processing on a Direct Chill Cast AA6082 Aluminium Alloy: Georges Salloum-Abou-Jaoude1; Dmitry Eskin1; Carla Barbatti2; Philippe Jarry2; Martin Jarrett2; Zhongyun Fan1; 1Brunel University London; 2Constellium
For many years now, ultrasonic melt treatment (UST) has proven itself to promote grain refinement in aluminium alloys. The current work presents cavitation-aided grain refinement obtained on commercial AA6082 DC-cast billets. Grain refinement was achieved while applying UST in the crucible away from the sump, prior to casting. Since in high strength alloys, Zr and Ti are commonly present as alloying elements for anti-recrystallization and corrosion resistance properties, their as well as UST parameters influence on the microstructure are studied and presented. Primary Al3(Zr1-x-y ,Tix , Siy) intermetallics were found in the centre of the α-Al grains. This suggests that UST may have forced the nucleation and refinement of primary intermetallics influencing the subsequent solidification process when Al3(Zr1-x-y , Tix , Siy) act as nucleation sites.
2:30 PM Cancelled
Microstructure Control in A356 Al-Si Alloy via Ultrasonic Melt Treatment: Waleed Khalifa1; Mahmoud Abdu1; Maiada Abdelrahman1; Yoshiki Tsunekawa2; 1Cairo University; 2Toyota Technological Institute
Ultrasonic treatment was conducted to study its effect on the size and morphology of the α-Al phase of the A356 Al-Si-Mg alloy. Treatments were carried out in the temperature range from 700 to 614 °C, i.e. from above the liquidus temperature (619 °C) to semisolid temperatures. The treatment times varied from 15 to 180 s. The results showed that ultrasonic treatment could control the alloy microstructure when applied in the liquid or semisolid states, and was most efficient when applied at a few degrees above the liquidus temperature, e.g., 620 °C, where globule size of 57 μm and roundness between 0.62 and 0.70 were obtained. Ultrasonic treatment times in the order of 15-30 s were sufficient to dramatically refine the size and alter the morphology of the α-Al phase. The refining effect observed in samples treated in semisolid state was due to solid fragmentation and dispersion, while in the liquid state, refining occurred most likely as a result of activation of non-equilibrium nucleation events which was confirmed from experimental simulations performed using succinonitrile polymer.
Shear Induced Grain Refinement of a Continuously Cast Ingot: Samuel Wagstaff1; Antoine Allanore1; 1Massachusetts Institute of Technology
A previous investigation  has demonstrated the wide variation of grain size found through the cross-section of a Direct-Chill (DC) cast ingot due to the position dependent solidification rate inherent to the process. Recently we have demonstrated  that the use of a turbulent jet as a metal entrance method has the potential to significantly reduce the size and variation in the grain structure. We here report a series of experiments investigating the influence of jet power on the grain size and distribution in Al4.5Cu DC cast ingots. Our findings indicate that significantly increasing the jet power does not appreciably decrease the grain size. Instead, a threshold jet power required for grain refinement is anticipated, beyond which there are only marginal improvements. S.R. Wagstaff, and A. Allanore: Light Metals, TMS, 2015, pp. 877-882 S.R. Wagstaff, and A. Allanore: Light Metals, TMS, 2016, pp. 715-720.
Grain Refiner Settlement in the Launder System of Twin Roll Casting and Application of Electromagnetic Stirring: Onur Birbasar1; Vedat Topaloğlu1; Murat Can Erdemir1; Cemil Işıksaçan1; Onur Meydanoglu1; Mert Günyüz1; Hatice Mollaoğlu Altuner1; Murat Dündar1; 1Assan Alüminyum
Al-Ti-B grain refiners are used as a grain refining agents in twin-roll casting. Although Al3Ti particles in the rod dissolve, principal inoculant of TiB2 remains undissolved and initiate heterogeneous nucleation. TiB2 particles with higher density than liquid Aluminum are in tendency to settle as they are released from the melting grain refiner rod. Experimental studies showed that Ti concentration varies at different depth of the liquid metal. The trajectories of the particles upon revealing from different position of the depth and their settlement were also simulated in FEA and experimental findings were confirmed. Well known method of electromagnetic agitation of liquid aluminum was implemented to the typical geometry of launder systems to keep the particles suspended. Samples gathered before and after activating the magnetic coil showed remarkable differences in their chemical and metallographic samples proving that, grain refiner particles can be kept in the stream without settlement and homogenously distributed.
3:45 PM Break
4:00 PM Cancelled
Thermal Analysis of Grain Refining in A319 Alloys: Waleed Khalifa1; 1Cairo University
Grain refining is an important technology in the modern aluminum foundry, since it provides several advantages to mechanical behavior and integrity of castings. In this work, thermal analysis of the A319 alloys was studied for the purpose of obtaining precise and repetitive cooling curves and hence accurate thermal analysis parameters. The main casting parameters such as cooling rate, alloy composition, and grain refiner level were considered and evaluated. The results showed that cooling conditions during thermal analysis experiments need to suitable to rapidly reach equilibrium between the solidifying melt and the mold. The time parameters give better control of grain refining than temperature parameters since they spread over wide ranges. The variation of Si and Cu levels resulted in composition-related changes of the thermal analysis parameters. In addition, it was also found that the sensitivity of the thermal analysis parameters to the variation of grain refiner level is highly impaired at slow cooling rates of 0.27 to 0.40oC/s.
Peritectic Coupled Growth Solidification - A Review: Peiman Shahbeigi Roodposhti1; Harold Brody1; 1University of Connecticut
Initiation and growth mechanisms of peritectic coupled growth (PCG) structures have been investigated to clarify parameters that play a significant role in PCG formation and stability. Three important alloys of Fe-Ni, Ni-Al and Ti-Al have been studied to reveal different mechanisms contributing in PCG formation. Types of PCG, the stability of the lamellar coupled growth and their morphological behavior are strongly dependent on G/V ratio (G: thermal gradient, V: growth rate), lamellar spacing and composition. Analogy between peritectic coupled growth (PCG) and eutectic coupled growth (ECG) is also a point of interest in this study. Further investigations in Ni-Al and Cu-Sn are necessary to clarify the PCG formation (nucleation/growth mechanism) in conventional G/V vs composition diagram.