Study on element mixing of titanium-stainless steel dissimilar metal welding pool and its effect on joint properties in nanosecond laser welding

During the melting welding of titanium-stainless steel dissimilar metals, intermetallic compounds typically form within the weld seam, significantly compromising its mechanical properties. This study firstly used nanosecond pulse laser achieved effective welding of thin wall titanium and stainless steels by adjusting the mixing ratio of metal elements in the weld seam. A computational fluid dynamics (CFD) calculation model for thin-walled stainless steel titanium nanosecond pulse laser welding was established, and the physical mechanism of element mixing behavior was revealed. The effects of varying heat inputs on fluid flow, mixing of elements, and the evolution of microstructure in the weld pool were investigated. Regardless of whether the melting pool penetrates the titanium thin wall, titanium elements easily accumulate along the edges of the melting pool on the stainless steel side. When the melting pool fully penetrates the titanium sheet, the average titanium content in the weld seam exceeds 23 at%. Conversely, when the bottom of the melting pool is situated at the center of the titanium thin wall, the average titanium content within the weld seam is approximately 9.99 at%. No intermetallic compounds were found in the weld seam the strength of the weld can be increased about twice. Controlling the average content of Ti element in the weld seam to not exceed 10 at% is a key factor in obtaining excellent mechanical properties of welded joints, and it providing new welding strategies for titanium-stainless steel metal welding.