Ultrasonic welding of magnetic hybrid material systems –316L stainless steel to Ni/Cu/Ni-coated Nd2Fe14B magnets

Abstract

The performance of electric sensors is continuously improving due to the demands of modern vehicles and electronic devices. Magnetic sensors are used in a wide field of applications. However, handling and mounting the typical high-performance rare earth permanent magnets are challenging due to their brittleness. A constant magnetic flux is a key property of the magnetic setup in many devices. State-of-the-art adhesive bonding of magnets in devices can cause problems due to the low durability and viscous behaviour of adhesive polymers, as the magnet may change its position and hence, the magnetic flux distribution in the magnetic setup changes.

Ultrasonic welding is a powerful technique to join hybrid material systems quickly and reliably, providing high joint strength, even for brittle materials such as glasses, ceramics and rare earth permanent magnets. The latter is being investigated in this work for the first time. The ultrasonic welding process was adapted to join 316L stainless steel, representing potential components of magnetic devices, to Ni/Cu/Ni-coated Nd₂Fe₁₄B. In addition to directly joined steel/magnet-hybrids, ductile aluminium and nickel interlayers were used in order to enhance the joint strength.

Process parameters were developed and evaluated considering the resulting shear strength of the joints. The highest shear strength of 35?MPa was achieved for 316L/Nd₂Fe₁₄B and 316L/Al/Nd₂Fe₁₄B, which is more than twice the shear strength of adhesively bonded joints of up to 20?MPa, according to the literature. The functional performance of the hybrid material systems, evaluated by the magnetic flux density of the hybrid material systems was the highest for directly bonded joints, and those with a nickel interlayer, which did not show any losses in comparison to the single magnet in its initial state. Joints with an aluminium interlayer showed losses of 3% and adhesively bonded joints showed losses of 7% of the magnetic flux density.

In summary, the results of this work indicate that ultrasonic welding is a suitable technique to improve the production process and performance of magnetic devices.