2020 The Author(s). This work focuses on ultrasonic melt treatment (UST) in a launder upon pilotscale direct chill (DC) casting of 152-mm-diameter billets from an AA6XXX alloy with Zr addition. Two casting temperatures (650 C and 665 C) were used to assess their effect on the resulting microstructure (grain size, particle size, and number density). Structure refinement results show the feasibility of UST in the DC casting launder. This is quantified through the corresponding reduction of grain size by around 50% in the billet center, or more towards the billet surface, reduction of the average Al3Zr particle size, and increase in the particle number density. A higher Al3Zr particle density was obtained when the alloy was cast at 665 C. Numerical simulation results and suggestions on how to improve the treatment quality of UST in DC casting launder are also provided.EPSRC (UK) projects UltraMelt2 (EP/R011001/1, EP/R011044/1,and EP/R011095/1)
