Investigation on Friction Welding of Pipes for Dissimilar Metals

Abstract

Friction Welding (FW) is well established, low-cost, and highly productive method for joining similar and dissimilar materials such as aluminium, steel, copper, titanium, and magnesium. However, the formation of intermetallic compounds, deterioration of mechanical properties, and parametric effects are issues that need to be considered as challenges of dissimilar joint of FW. The Board of Research in Nuclear Sciences (BRNS), an organisation in India, is funding this project, which has the project number 39/14/02/2018-BRNS/39002. In this case study, the joint characteristics, mechanism, microstructural changes, and process parameters of a dissimilar pipe system made of Al-SS and Cu-SS FW are examined. Six different pipe joint configurations are examined here, including pipe dimensions 1 (OD 600.33 mm and WT 3.9 mm), pipe dimensions 2 (OD 88.90 mm and WT 5.4 mm), and pipe dimensions 3 (OD 114 mm and WT 6.5 mm) made of Al-SS and the same as Cu-SS. However, with the exceptional pipe dimension 1 (OD 600.33 mm and WT 3.9 mm) in Cu-SS, each pipe joint obtained more than 60% of joint strength compared with PM of Al and Cu metals. Additionally, to look into the FW parameters of rotational speed, duration, and pressure that cause the observed influence on the joint characteristics and enhance mechanical strength while maintaining constant the other FW process parameters. Additionally, only a few research articles on pipe to pipe joints have been noted in previously published articles, whereas several articles have reported solid to solid joints with similar and non-similar metal pairs. For these reasons, this research is distinct from that found in previously published articles. The quality of the welds produced under the different process parameters is initially assessed by the visual inspection of flash morphologies and macrographs. After that, the welded specimens are subsequently evaluated with microstructural features, tensile properties, fracture analysis, hardness profile analysis, scanning electron microscopy, electron dispersive spectroscopy, electron backscatter analysis, and X-ray diffraction analysis. The present investigation reveals that in pipe configuration the welded samples passed in a vacuum and cryogenics test as per the requirement of the cryogenics heat exchanger application. Also, near the weld line, the flash formation is developed on the Al and Cu side only, whereas SS side no flash formation is reported. Throughout the experiment, soft materials are mounted on the stationary side, wherein the rotating side SS is fixed. Moreover, the microstructure variation is observed on the Al and Cu side while SS side limited variation is reported. Materials flow of Al and Cu are affected by high pressure, temperature, and rotational direction of the SS metal. In a fracture surface investigation, the samples are broken into the interface and parent Al & Cu side. Also, the interface zone plays a significant role in the mechanical characteristics which leads to improving the tensile strength and hardness value. Involvement of the elements in the interface zone plays the dominant role in the characteristic of the joint, wherein equally distributed Fe, Al, and Fe, Cu elements in the faying zone improve the properties of the joint. Based on the mixture of the elements new intermetallics phases are developed in the interface area which is identified during the XRD test. These intermetallic compounds participated in the microhardness test due to the variation noted in the interface zone and nearer the welding zone. Keywords: - Aluminium, copper, dissimilar metals, friction welding, joint properties, microstructure investigation, stainless steel.