Nd:YAG laser welding of dissimilar metals of titanium alloy to stainless steel without filler metal based on a hybrid connection mechanism

Abstract

In this paper, Nd:YAG laser welding of TC4 Titanium (Ti) alloy and SUS301L stainless steel (SS) dissimilar metal material was carried out without filler metal by laser biasing. The microstructure and fracture mode of the joint were analyzed by scanning electron microscope (SEM), energy dispersive instrument (EDS), and X-ray diffractometer (XRD). The mechanical properties of the joint were evaluated by a tensile test. The results showed that when the peak temperature was 1116℃, the liquid phase existed only in the narrower region of the Ti-SS interface, and the eutectic reaction zone formed a reaction layer, which was mainly composed of β-Ti solid solution. Ti-Fe intermetallic compound (TiFe, TiFe2) was formed at the Ti alloy-SS interface by heat conduction of the unmelted Ti alloy. The TEM analysis confirmed the presence of the β-Ti and TiFe2 phases. The nucleation and growth of the reaction layer depended on the diffusion rate and atomic concentration of Ti and Fe atoms. The growth of the reaction layer could be effectively promoted by increasing the welding heat input, increasing the peak temperature of the Ti-SS interface and prolonging the reaction time. The tensile strength of the joint could be reached 336MPa and an elongation was 0.13 %. The eutectic reaction method could control the thickness and size of the Ti-Fe intermetallic compound at the interface of the Ti alloy-SS and improve the mechanical properties of the joint.