Mechanistic Insights into Intermetallic Compound Formation with Varying Brazing Temperature in Induction Brazed Al/Steel Joints

Abstract

The soundness of brazed joints and interface characteristics are significantly governed by brazing temperature and filler besides, other process parameters such as clearance and surface-preparation. In this work, attempts have been made to study the effect of brazing temperature (585-630 °C) during induction brazing of AA6061 and SS304 using Al-10Si filler as it affects the mechanical and metallurgical characteristics of interface. Metallographic analysis was conducted on Al/steel brazed joint in terms of microstructure and compositional variations. Optical and field emission scanning electron microscopes were employed to study the brazed joint, while x-ray diffraction and energy-dispersive x-ray spectroscopy were carried out for determination of intermetallic compound (IMC) composition and phase analyses at steel/filler metal interface, respectively. Mechanical properties of the joints were assessed through lap shear test and nano-indentation. A continuous, defect-free FeAl₅Si IMC layer with a thickness of 3.5 ± 0.5 µm and a nanohardness of 6.3 GPa was obtained at 615 °C brazing temperature, resulting in a joint strength of 7.4 kN. However, at 630 °C, a thicker 7.4 ± 0.6 µm IMC layer formed, with 14% increase in nanohardness and 15% decrease in joint strength. The results have been discussed based on a comprehensive microstructure analysis and evaluation of mechanical properties.