In this paper, a TC4 alloy/304 stainless steel (SS) explosion welded composite plate was used as an interlayer to join TC4 alloy and 304 SS dissimilar metals by double-pass laser welding. The unmelted TC4 alloy and 304 SS were retained on the interlayer during laser welding as a diffusion barrier to prevent Ti and Fe alloying elements from diffusing into the melt pool to form Ti-Fe brittle intermetallics. The first laser was focused on the TC4 alloy-TC4 alloy interface and the molten TC4 alloy was used to join the base material TC4 alloy to the interlayer TC4 alloy, and formed a mixed weld zone. The second laser was focused on the 304 SS-304 SS interface, using molten 304 SS to join the base material 304 SS to the interlayer 304 SS, and formed the other mixed weld zone. Double laser welds of TC4 alloy and 304 SS using TC4 alloy/304 SS composite interlayer not only improved the interfacial microstructure but also enhanced the mechanical properties of the joint. Tensile failure occurred in the middle layer of unmelted TC4 alloy with a maximum tensile strength of 835 MPa.
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