Ductile iron has been extensively used in various automotive components such as crankshafts and differential housing owing to its relatively low density and capacity for significant tensile strength. 20MnCr5 is a robust and tough alloy steel commonly employed in the production of gears and shafts. Establishing effective welding between the shaft body and the gear material is a significant research challenge. However, the notable disparity in the thermal properties between ductile iron and alloy steel hinders the performance of the welding joint. The high carbon content of ductile iron promotes carbon segregation at the welding interface and exacerbates the formation of microcracks, thereby considerably increasing the complexity of the welding process. Owing to its high energy density, laser welding offers the advantage of generating welds with more precise heat-affected zones. In this study, a novel continuous-pulse coaxial dual-beam laser is employed as a welding heat source to enhance the surface quality of the weld seam. The high-quality welding of ductile iron and alloy steel is achieved by decreasing the laser input power and diminishing pore formation. We hope that our novel welding strategy and findings will be helpful in understanding the bonding mechanism of ductile iron and alloy steel and provide more application space for their connectors.

In this study, QT500-7 and 20MnCr5 are employed as the base materials, with ERNiCr-3 as the filling wire. A novel continuous-pulse dual-beam laser is used as the heat source. First, the pulsed laser power is varied with a constant continuous laser power to determine the optimal combination of heat sources. The laser action position is then adjusted to further enhance the weld strength. Microstructures are observed using a metallographic microscope, and mechanical performance testing and analysis are conducted using a tensile testing machine. The microhardness of the weld is measured using a microhardness tester. Additionally, the fracture behaviors of different specimens are analyzed using a field-emission scanning electron microscope.

The use of a continuous-pulse coaxial dual-beam laser as a welding heat source (Fig. 2) produces high-quality welding joints. When the pulsed laser power is varied, the weld formation varies considerably (Fig. 4). The weld seam is found to have no defects, such as cracks or pores. When the laser action position shifts toward the steel side, the heat input on the ductile iron side gradually decreases. This reduction in the heat input suppresses the diffusion of carbon, leading to a significant decrease in the hardness values of the heat-affected and bond zones on the QT500 side (Fig. 13). The cross-sectional morphology of the weld reveals significant changes in the melting amount of the QT500-7 side base material, with the centerline shifting toward the ductile iron side when the laser action position is changed (Fig. 6). The segregation line of carbon caused by the high carbon content of the nodular cast iron is solved by changing the laser position to reduce the heat input on the side of the nodular cast iron (Fig. 7). The best mechanical properties of the joint are obtained under a pulsed laser power of 440 W and offset of 0.2 mm. In summary, a continuous-pulse coaxial dual-beam laser can yield high-quality welding joints. Better dual-beam laser welding parameters can be achieved by adjusting the laser power and action position. Furthermore, carbon segregation issues can be effectively resolved by reducing the heat input on the side of the nodular cast iron by changing the laser action position, and pulsed laser stirring proves useful.

In this study, a coaxial dual-beam laser welding technology is proposed to address the challenges of welding ductile iron QT500 and alloy steel 20MnCr5. The main problems are the precipitation of martensite and ledeburite in the heat-affected and bond zones on the QT500 side, which results in carbon segregation. The pulsed laser power and position are adjusted in this study. When the laser action position is shifted toward the steel side, the decreased heat input suppresses the diffusion of carbon, leading to a significant decrease in the hardness of the heat-affected and bond zones on the QT500 side. The best mechanical properties are achieved under a pulsed laser power of 440 W and laser offset of 0.2 mm. The continuous-pulse coaxial dual-beam laser welding technology not only improves the carbon segregation phenomenon on the ductile iron side but also reduces the formation of welding cracks. Overall, the proposed novel coaxial dual-beam laser welding technology is effective in improving welding quality, specifically for ductile iron and alloy steel dissimilar metals. The joint exhibits high-quality and high-performance characteristics by reducing carbon segregation and minimizing hardness values. This study advances the field of welding and provides a potential solution for the welding of dissimilar metals with different material properties.