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Thin copper materials are difficult to weld using infrared lasers (IR) due to their low energy absorption. A blue laser with a wavelength of 450 nm strongly increases energy absorption and successfully realized the microjoining of a copper material with a thickness of 0.1 mm. The dynamic behaviors of a thin molten pool were investigated by a numerical simulation using a new blue laser heat source model. At both the top and bottom surfaces of the thin molten pool, the liquid metal flowed outward under the driving of Marangoni stress. The stability of the thin molten pool was studied, showing that Marangoni stress promoted the melt-through of the thin molten pool, while the viscous resistant stress, buoyant force, and surface tension pressure had minor influences on it. The Peclet and Marangoni numbers were adopted to predict the stability of the thin molten pool.

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