The effect of electron beam welding parameters on the microstructural characteristics and mechanical properties of dissimilar joint between 17-4PH steel and Ti6Al4V alloy

This study aimed to investigate the effect of electron beam welding parameters on the microstructural characteristics and mechanical properties of the dissimilar joint between 17-4PH precipitation hardening stainless steel and Ti6Al4V alloy. For this purpose, the welding of these two alloys was done without an interlayer and with an interlayer of copper with a thickness of 0.8 mm. Two different welding speeds of 0.7 and 0.9 m/min with four levels of beam offset  (0, 0.2, 0.4 and 0.6 mm) from the center of the interlayer towards the steel were used to perform experiments. The results show that in the direct welding of titanium and steel, the joint structure consists of TiFe and TiFe2+TiCr2 intermetallic compounds with high hardness (about 900 Vickers). In the welding of titanium and steel by using the copper interlayer, the structure in the weld pool and the interface between the weld pool and steel includes a solid solution of copper and TiFe2 intermetallic compounds, and at the interface between the weld pool and titanium includes Ti+Ti2Cu and TiFe. The hardness of the welding zone in the samples welded with copper interlayer is about 400 Vickers. The highest value of hardness is observed at the interface between the weld pool and titanium alloy, as well as at the interface between the weld pool and steel, which is due to the presence of intermetallic compounds with high hardness. By increasing the welding speed and beam offset, the hardness decreases, which is due to the reduction of brittle intermetallic compounds in the joint structure. The welded sample with a welding speed of 0.9 m/min and beam offset of 0.6 mm has the highest shear strength equal to 160 MPa.