Effect of mechanical vibration on the microstructure and mechanical properties of CO2/MAG welded joint of Q345B steel

Vibration assisted welding (VAW) has emerged as a successful replacement for heat treatments of arc welds to refine grain, reduce residual stresses and distortions and thus to improve its mechanical properties. In this paper, mechanical VAW would be applied on the 8 mm thickness Q345B steel CO2/MAG filler welding, and the filler materials are solid core welding wire and flux-cored welding wire, respectively. The results show that: with the application of vibration, the proeutectoid ferrite in the weld area becomes finer, and the dendrites in the columnar crystals become significantly finer and more evenly distributed. The microhardness value of the weld zone in the welded joint with vibration is higher than that in the welded joint without vibration. The tensile strength of the welded joint increased from 502.5 MPa to 551.0 MPa at the motor speed of 2700 r/min when using solid core welding wire, increase nearly 10%. While, the tensile strength was deteriorated after the motor speed increased to 3600 r/min, which decreased to only 412 MPa, and the decreasement reached 25% comparing with the motor speed of 2700 r/min. During the VAW, the tensile strength and impact value of the welded joints fabricated by flux-cored welding wire are obviously better than that fabricated by solid core welding wire.