**2. Materials and Methods**

The schematic illustration of the experimental apparatus is shown in Figure 1. The traveling magnetic field was created by means of applying out-of-phase alternating current (AC) currents (50 Hz) to six coils with a star arrangement connected vertically one upon the other. As a result, a downward meridional traveling Lorentz magnetic field was induced in the sample melt. This technique has already been detailed in previous work [15]. A nonmagnetic stainless-steel frame was designed and assembled to hold the sample firmly. The sample had a diameter of 3.5 mm and a length of 100 mm and was placed in a quartz tube fixed in the center of the cavity. The nonmagnetic stainless-steel frame, which allowed water to stream in and out, was installed and thus enabled the equipment to control the cooling rate by adjusting the flow rate of the streaming water. An electric heating furnace was used to heat and melt the sample. The furnace was removed through the opening of the upper cylinder when the TMF generator was applied.

The Al alloy studied in this work had a composition of 3.8Cu-0.4Mn-0.3Ti-0.1Cd-0.25V-Al (bal. in wt. %). The sample was placed in the center of the TMF generator and the heating furnace was set around the sample and turned on to heat and melt the sample up to 1023 K. The molten sample was kept at this temperature for 10 min before the furnace was removed. Then the TMF generator was applied at different stages of the cooling process to the ambient temperature. The magnetic flux densities of the TMF were set as 24 mT, 32 mT, and 48 mT, respectively. For comparison, a sample was also prepared without TMF application.

The microstructures of the as-cast samples were examined by scanning electron microscopy (SEM) (Quanta 200FEG, FEI, Hillsborough, OR, USA) in the cross-section of the sample and 3D X-ray microtomography. The X-ray microtomography was carried out at the BL13W1 beamline in the Shanghai Synchrotron Radiation Facility (SSRF). An X-ray energy of 30 keV was used to penetrate a cylindrical sample of 3.5 mm in diameter and 2–5 mm in height with a voxel size of 3.7 μm. A 2048 × 2048 pixel CoolSnap K4 CCD camera (Coolsnap, Photometrics, Tucson, AZ, USA), coupled with a CdWO4 scintillator screen, was used to record the projections. Each 3D data set contains1440 projections that were collected with an exposure time of 1 s. The projections were reconstructed using a filtered-back-projection algorithm. The raw images were preprocessed in Image J (NIH, Bethesda, MD, USA) and then further analyzed in Avizo (VSG Group, Bordeaus, France). A median filter was applied in Avizo to reduce the noise of the image. The tensile tests were conducted on an electronic universal mechanical testing machine (Instron5569, Instron Co., Canton, OH, USA) at an initial strain rate of 5 × <sup>10</sup><sup>−</sup>2. The length of the sample gauge was 20 mm.

**Figure 1.** The schematic illustration of the experimental apparatus.
