Influence of laser-Sn powder coupling on microstructure and mechanical properties of fusion welded AZ31B-alloy to DP590-steel

Microstructure and mechanical properties were studied in fusion welded AZ31B-alloy to DP590-steel at different weld conditions such as with varying laser power, and Sn powder added to lap joint with prefabricated width settled concave groove. Temperature field and flow field for laser welding including chemical potential of each element are also calculated. The results suggested that Al atom tends to diffuse toward Fe side which contributes to form a FeAl compound reaction layer at interface. Meanwhile, Al accelerates the diffusion of Sn and Fe as a catalyst. The shear force of joint climbs at first, then declines, and the maximum value reaches 1711 N when laser power is 1 kW, which is improved by 38% compared with that of 0.9 kW. The improved joint properties are dominated by metallurgical regulation of Sn power, which benefits from the accelerated flow of molten pool and increased temperature leading to the phase composition transformation from alpha-Mg + Mg2Sn + FeAl to alpha-Mg + Mg2Sn + FeSn + Fe3Sn + FeSn2 + FeAl in direct laser irradiation region. However, under the condition of excessive laser power, overreaction occurs at side boundary interface, which leads to the formation of thick IMC and the production of hot crack defect, thus the joint performance decreases.

Automated summary

Microstructure and mechanical properties were studied in laser fusion welded AZ31B-alloy to DP590-steel. The diffusion behavior of Al and Sn, as well as the formation of FeAl compound reaction layer, were investigated. The addition of Sn powder improved the joint properties by accelerating the flow of molten pool and leading to phase composition transformation. However, excessive laser power resulted in overreaction and the production of defects, leading to decreased joint performance.