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Formation process of reaction layer between aluminium alloys and stainless steel by friction welding

There are many instances where sound joints cannot be obtained when welding dissimilar metals due to the formation of large quantities of brittle intermetallic compounds in the weld zone during normal fusion welding processes. The friction welding process, in which the energy required for joining is obtained by means of friction between the materials to be welded, is extremely appropriate to join dissimilar metal materials because of the short joining time of just a few seconds and the low heat input. Friction welding between aluminium alloy and stainless steel has been reported for the combination of 1000, 5000 and 6000 series aluminium alloys and austenitic stainless steel." The formation of an intermetallic compound layer (reaction layer) consisting of Fe2Al5, Fe4Al13 and FeAl3 can be seen at the interface of friction welded aluminium and steel. The reaction layer is reported to grow with increasing friction time;' however, friction welding has a large number of parameters (friction time, friction pressure, speed of rotation, upset time, upset pressure) and there are many unclear aspects regarding its formation and development process. In addition, the temperature at the weld interface complicates the explanation of the friction welding mechanism; the temperature rises close to the melting point in mere seconds and measurement of temperature is extremely difficult because the weld interface is rotating at a speed of several thousand rpm. Thus, to date, numerous temperature analyses and temperature measurements near the interface have been attempted using difference calculus and finite element methods." In this report the microstructure at the weld interface between stainless steel and aluminium alloy was observed, the temperatures near the weld interface were measured and the formation process of the reaction layer was investigated.