The surface quality control of extruded products is a critical concern in the home appliance manufacturing industry owing to the increasing need for products with a high surface quality, in addition to the essential mechanical properties of the final product. The underlying issue with achieving high-quality extrusion products is that surface defects, especially those resulting in surface gloss differences, called white line defects, are only observed after surface treatment. In this study, we aim to investigate the cause of white line defect generation on the surface of an extruded product. Accordingly, an experimental extrusion program is established using an L-shaped die that has a noticeable change in its bearing length along the inner corner of its cross-sectional profile. Laboratory-scale experiments were performed for the L-shaped extrusion of homogenized Al 6063 alloy at various ram speeds, in order to induce surface defects, considering the production yield rate required for mass production. Subsequently, the microstructural changes near the surface failure region were investigated using an arbitrary Lagrangian–Eulerian (ALE) technique-based thermomechanical finite element (FE) analysis. To scale-up the defect observation method from laboratory-scale to production-scale manufacturing and confirm the reproducibility of the surface defect, scaled-up L-shaped extrusions were performed in an actual industrial production line. Finally, the potential cause of white line defect generation is discussed by comparing the numerical and metallurgical analyses, including the scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) observations.

For developing subminiature and highly integrated multilayer inductors, soft magnetic powder was used; however, its ferrite magnetic component is characterized by high resistivity and reduced direct current saturation, leading to the deterioration of the inductor under high currents. Therefore, herein, to improve the electromagnetic properties of thin-film inductors, Fe nanopowder was used to increase the volume fraction of magnetic sheets. Surface treatment was performed by using silane coupling agents, which improved the bonding strength and dispersibility of the Fe nanopowder with a heterogeneous epoxy binder. For uniform surface treatment on the nanopowder, the silane-treated powder was aged for 24 h, at a temperature of 3 °C. The surface-treated Fe nanopowder was used with a mixing ratio of the soft magnetic powder (coarse:fine:nano) of 7:2.5:0.5 wt.%; this was successful in producing a flexible and highly densified magnetic sheet. As a result, the volume fraction of the magnetic sheet for thin-film inductors to which a low-temperature aging-treated nanopowder was applied was significantly improved.

When the uniformity of the magnetization yoke is low, a mismatch occurs between the physical rotation center and the center due to the magnetic force after magnetization. This discrepancy in rotation can cause issues such as vibration and noise during high-speed rotation, which in the long term leads to a decrease in the lifespan of the motor. In addition, in order to minimize the problem of motor lifespan when a vehicle is used for more than 10 years after purchase, the problems caused by magnetization should be solved as far as possible. In this study, magnetization yokes were designed in various ways to optimize the factors that affect the magnetic properties after the magnetization of the Nd₂Fe₁₄B permanent magnets used in electric motors. In the case of a 50 µm deviation between the coils wound inside the magnetization yoke, the magnetic property imbalance of the Nd₂Fe₁₄B magnets and the motor characteristics are not significantly affected after magnetization. However, when the center of the coil wound inside the yoke is shifted from the center of the yoke, the magnetic field is generated unevenly, which degrades both the magnetic and motor characteristics of the Nd₂Fe₁₄B magnet. Therefore, it is very important to control the center of the coil that generates the external magnetic field in the magnetized yoke in order to magnetize the Nd₂Fe₁₄B magnet with excellent magnetic properties.