Abstract
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 α-Mg + Mg2Sn + FeAl to α-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.
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