Journal of Welding Science

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 stainless steel and Ti6Al4V alloy. For this purpose, the welding of these two alloys was performed with an copper interlayer with a thickness of 1 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 accomplish the experiments. The results show that by using the copper interlayer with thickness of 1 mm, the cracks caused by the formation of intermetallic compounds are removed from the weld pool. At the interface between the titanium and the weld pool, at the beam offset  of 0 and 0.2 mm, a solid solution of copper and TiCu2 intermetallic compounds is formed, while at the beam offset  of 0.4 and 0.6 mm, a solid solution of copper and TiCu intermetallic compounds is formed. The weld pool, at the beam offset  of 0 and 0.2 mm, consists of TiCr2+TiFe2 intermetallic compounds while at the beam offset  of 0.4 and 0.6 mm, solid solution of iron (α-Fe), solid solution of copper and TiCu intermetallic compounds are formed. The highest value of hardness is observed at the interface between the weld pool and the titanium alloy, as well as at the interface between the weld pool and the steel, which is due to the presence of intermetallic compounds with high hardness in these regions. By increasing the welding speed and the beam offset, the hardness value decreases, which is due to the reduction of brittle intermetallic compounds in the joint structure. By increasing the beam offset from 0.4 mm to 0.6 mm at the speed of 0.7 m/min, the shear strength increases from 180 MPa to 210 MPa and at the speed of 0.9 m/min, the shear strength raises from 230 MPa to 250 MPa. The welded sample with the welding speed of 0.9 m/min and the beam offset of 0.6 mm has the highest shear strength equal to 250 MPa. The failure in all samples happened at the interface between the weld pool and the titanium alloy, which shows that the weakest region in the joint is this interface.

Welding is one of the methods of surface repair of cast irons. In this study, surface repair of gray cast iron was first performed by gas metal arc welding method with ER70S-6 welding wire under inter-pulse current, heat input of 393 J/mm and dilution of 17%. Also, to compare the results, two samples were welded with ENi-CI and E6013 covered electrodes. Microstructural studies showed that the microstructure of the interface of the sample is composed of martensite with fine lathes and upper bainite. Despite the presence of cementite (Fe₃C) next to alpha iron (α-Fe) in the interface area, the formation of incomplete mixing zone with bainite lathes in the ferrite zone has led to increased toughness and prevented crack formation. The hardness of the ER70S-6 sample was similar to that of the E6013 sample at the interface, at about 809 Vickers, which is 334 Vickers higher than the hardness of the ENi-CI sample. The results of the open circuit potential and potentiodynamic polarization tests showed that the ER70-CI sample, with a corrosion potential and current of -653 mV and 6.8 μA/cm², had a higher polarization resistance and was more resistant to galvanic corrosion than the ENi-CI sample (-622 mV and 8.9 μA/cm²).