Microstructures of friction welded joint of 6061 aluminum alloy to 304 stainless steel.

Abstract

A 6061 aluminum alloy was joined to a 304 stainless steel by friction welding. The structure of aluminum alloy was refined in the vicinity of the weld interface. However, the Vickers hardness was decreased near the interface since the precipitates were dissolved in the aluminum alloy matrix by the friction heat. The width of heat affected zone (HAZ) was decreased as the increase in the friction and upset pressure (P1 and P2) increased. The sound joints were obtained welded by P1 =30 MPa, P2 =60 MPa and t1 (friction time) ≥2.0 s. The higher P1 made the joint strength decrease owing to the excess formation of brittle intermetallic compounds at the weld interface. The inter-diffusion of each element through the weld interface were revealed using TEM–EDS analysis. Fe2Al5 was mainly formed at the weld interface. The welding temperature was estimated to be under the eutectic temperature of Al/Fe system(925 K) by the thickness of intermetallic compound. Therefore, it is assumed that this friction welding was carried out in solid state in this system.