Microstructure and mechanical properties of copper-steel TIG filling-wire welding joint assisted by AC magnetic field

Abstract

By adding a longitudinal AC magnetic field and using HS201 pure copper wire as the filler metal, TIG butt joint experiments were conducted on T2 copper and Q235 steel plates, both with the thickness of 2 mm, to study the joint formation, organization and mechanical properties when the magnetic field was added. The results show that the surface of weld zone is formed well after adding magnetic field. The best technological parameter is as follows: when welding current I=95 A, welding speed v=95 mm/min, magnetic field frequency f=25~35 Hz, magnetic field current IE=0.4~0.6 A, the mechanical properties of the joint is good, and the maximum tensile strength is 223.5 MPa, which is 44.5% higher than that without magnetic field. Copper-steel TIG welding joint is mainly divided into steel-HAZ, fusion zone, weld zone and copper-HAZ. After the addition of AC magnetic field, the morphology of ferrite in steel side heat affected zone changes from massive to needle like and lateral strip; the microstructure of weld zone changes from cellular crystal to fine and uniform cellular dendrite; the microstructure of copper-HAZ is obviously refined. After adding magnetic field, the types of phases in the fusion zone and weld zone of the joint have no change, which are composed of (α-Fe)+(ε-Cu); the solute segregation in the fusion zone is improved, and the (α-Fe)+(ε-Cu) particles change from coarse dispersion to fine aggregation; the microstructure of the weld zone is refined and its uniformity is obviously improved, which makes the hardness gradient of fusion zone and weld zone relatively decrease.

Keywords

• longitudinal alternating magnetic field
• magnetic field current
• magnetic field frequency
• solute segregation
• hardness gradient