Spreading behavior of molten solder with alternative currents under the action of electromagnetic ultrasound

A novel electromagnetic ultrasonic-assisted spreading with molten Sn−9Zn solder on the surface of SiC ceramics was developed. The distribution and strength of the magnetic induction of an alternating magnetic field, the strength of the static magnetic field, and a numerical simulation of molten solder spreading behavior were investigated. The strength of the alternating magnetic field that was induced around the coil was proportional to the peak current, and the alternating current was induced in the periphery to change the direction periodically. The surface of the solder collapsed and spread under the action of electromagnetic ultrasound, accompanied by a vibration phenomenon on the solder surface, and subsequently, part of the solder below the coil broke and splashed, and the solder at the center constricted. The maximum spreading radius depends on the peak current and reached 12.4–14.1 mm. The direction of the Lorentz force pointed to the external solder overall, and gradually pointed to the surface of the substrate at the edge of the solder. The repulsion between the coil and solder biased the direction of the Lorentz force inside the solder. The horizontal Lorentz force of the solder below the coil reached 21.32–213.07 kN/m3, and the vertical Lorentz force was within 10.4–103.9 kN/m3 at different peak currents. This new welding method can be brazed without direct contact with the substrate or solder, which prevents substrate cracking by ultrasonic vibration and has the advantages of easy process control, and protection of the experimental material.