Mechanical properties and microstructure of the C70600 copper-nickel alloy and C46500 brass joint using brazing technique

Abstract

Naval brass (C46500), due to the presence of tin in this alloy, it exhibits high resistance to atmospheric and aqueous corrosion. This type of brass is widely used in various industries, including marine applications, electrical components, etc. The C70600 copper-nickel alloy, due to the formation of a solid solution, maintains high ductility while increasing tensile strength. High resistance to seawater corrosion, attributed to significant amounts of manganese and iron, are among the key characteristics of this alloy. The joining of these alloys in marine applications are required. Considering the formation of solid solutions and intermetallic compounds and their impact on mechanical properties, controlling their amounts is crucial for achieving optimal results. Brazing is known as an effective method to join these base materials. Since temperature and time are two critical parameters in brazing, influencing the formation of precipitates, this study focuses on optimizing these conditions to achieve desirable microstructural and mechanical properties. The brazing process was performed under 16 different conditions including 650, 680, 710, and 740 °C for 1, 5, 15, and 30 mins. To study the microstructure of joints, and the related phase transformations in the joint region, optical microscopy, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) were used. Mechanical properties of the samples were evaluated through strength testing and micro hardness measurements. The results indicate that with increasing temperature and duration of the joining process, the width of the thermally solidified zone decreases due to the increased diffusion rate, while the width of the isothermal solidification zone increases. Moreover, increasing the brazing time promotes phase segregation. The highest strength, measured at 106.4 MPa, was achieved for the sample joined at 710 °C for 15 mins, with the fracture surface displaying a mixed ductile-brittle mode.