Microstructure and forming control of laser welding-brazing joint of magnesium alloy and steel dissimilar materials

Abstract

The laser welding-brazing technology assisted by alternating magnetic field was adapted to AZ31B and Q235. In order to improve the mechanical properties of the joint, Ni interlayer was added to coordinate the metallurgical connection between magnesium alloy and steel, longitudinal alternating magnetic field was applied to optimize the weld forming. The results show that the IMC layer of the joint in fusion welding zone assisted by alternating magnetic field with Ni interlayer is composed of dendrite or continuous nanoscale layered AlNi phase. Magnesium alloy and steel realizes metallurgical connection by laser welding-brazing. The thickness of Fe-Ni solid solution decreases and extends into the weld of magnesium side after the application of alternating magnetic field, and increases the interface bonding area increases by the gully like Fe-Ni solid solution. The actual interface connection length is the main factor affecting the tension shear line load of the joint. The actual interface connection length and the tension shear line load of the welding-brazing joint exhibit first increasing and then decreasing trend as the increase of the magnetic field intensity (B). When the laser power P=1250 W, welding speed v=20 mm·s-1, B=10 mT, frequency f=35 Hz, magnesium alloy and steel are able to achieve the metallurgical connection by the addition of Ni interlayer and the weld forming of the joint is optimized by applying longitudinal alternating magnetic field, the tension shear line load of the joint is the highest, reaching 163 N/mm.

Keywords

• laser welding-brazing
• alternating magnetic field
• metallurgical connection
• weld forming
• tensile shear strength