Kinetics of intermetallic compound layers between AISI 321 stainless steel and molten aluminum

Abstract

The interfacial reaction between liquid aluminum and solid steel is critical to understanding the evolution of intermetallic compounds (IMCs) in the brazing and weld brazing processes of aluminum-to-steel dissimilar alloys. In this study, hot dip aluminizing of AISI 321 stainless steel at different temperatures was conducted to reveal the influence of reaction temperature and time on interfacial IMCs. Electron microscopy analyses were employed to investigate the interfacial microstructures. A single layer of θ-Fe4Al13 was observed at 700°C. In contrast, the IMCs of interfaces dipped at 800–1000°C consisted of a thin inner layer of η-Fe2Al5 + ζ-FeAl2 next to the steel and a thick layer of θ-Fe4Al13 close to the aluminum. For the inner layer, the thickness increased with increasing dipping temperature and time. Its growth was described by a parabolic rate law, which suggested a diffusion-controlled mechanism at the interface. An activation energy of 66.5 kJ mol−1 was obtained. For the Fe4Al13 layer, the thickness evolution at different temperatures was different from that of the inner layer, with a thick IMC layer at 700°C, a thinner IMC layer at intermediate temperatures (from 800 to 900°C), and a slightly thicker IMC layer from 950 to 1000°C. The growth kinetics of Fe4Al13 at 700°C were controlled by diffusion, interfacial reactions, and dissolution mechanisms. The evolution of Fe4Al13 between 800 and 1000°C was governed by diffusion and dissolution mechanisms. The appearance of the inner layer and the evolution kinetics of Fe4Al13 accounted for the decrease in thickness with increasing temperature between 700 and 900°C.