Journal of Welding Science

This present study aimed to create an Al6061-St52 dissimilar joint and investigate the effect of the transverse speed by the friction stir welding process. Welding aluminum to steel is rugged by fusion methods because of the formation of brittle intermetallic compounds (IMCs). Therefore, to designate optimal parameters, acceptable IMC thickness, and mechanical properties determined. This research carried out different three transverse speeds of 16, 40 and 85 mm/min (with a constant pin offset of 0.2 mm). Geometry of tool's pin radius and height is 4mm and 1.8mm, respectively. In the transverse speed parameter, the highest ultimate tensile strength (UTS) of 200 MPa was obtained at 85 mm/min. According to the Energy Dispersive X-ray Spectroscopy results, an IMC layer formed in the joint interface. The heat input rate was calculated to designate the optimal parameters. In tensile specimens, fracture mainly occurred in the joints and within the aluminum stir zone due to the combination of thick IMC layer and steel fragments, respectively. The micro-hardness measurement results showed that at (85 mm/min) the hardness values were HV 75 in the aluminum stir zone and HV 315 in the AS vicinity of the interface region. This hardness value is much higher than the base metals (Aluminum base metal is an average of HV 53 and an average steel base metal of HV 245).

In this research, the transient liquid phase bonding of St52 carbon steel to WC-Co cermet using a copper interlayer with 50 μm thickness was done. For this purpose, samples were jointed to each other at a constant temperature of 1100 ºC and bonding times of 1, 15, 30, and 45 min. The microstructure of the joints was examined using an optical microscope and scanning electron microscope equipped with energy-dispersive X-ray spectroscopy. XRD analysis was also used to investigate the effect of bonding on the phase changes of the bonding area. Microhardness and tensile shear tests were also conducted to study the mechanical properties of the samples. Microstructural investigations showed the formation of three different zones including isothermal and athermal solidification zones and DAZ in the WC-Co base material side, which determine the characteristics of the samples. The isothermal solidification zone contained a Fe-rich solid solution and the athermal solidification zone contained a Cu-rich solid solution. η phase was not formed in the DAZ of WC-Co cermet at bonding times of 1 and 15 min. This phase was formed in the DAZ of WC-Co cermet by increasing the bonding time to 30 and 45 min. The microhardness studies showed that all samples had the same trend. Maximum microhardness was 1100 HV which was related to WC-Co base cermet and the lowest microhardness was about 220 HV which was related to steel base metal. Also, the maximum tensile-shear strength of the bonded samples was about 180 MPa for a bonded sample at a bonding time of 15 min, which was due to the increase in the volume fraction of iron-rich solid solution, as well as proper microstructural continuity and the presence of an optimal amount of copper-rich phase in the microstructure.