2008 Volume 26 Issue 3 Pages 235-241
Tandem beam brazing with the aluminum filler metal (BA4047) was conducted in order to develop the fluxless laser brazing technique of aluminum alloy (AA6022) to galvanized steels (GA and GI steels). Laser powers of tandem beam and offset distance of preheating beam from the root to the steel base metal were varied. Sound braze beads could be obtained by optimizing the preheating and main beam powers under the offset distances of 0-1mm. A small amount of zinc remained at the braze interface between galvanized steels and the braze metal. The reaction layer consisting of Fe-Al intermetallic compounds was also formed at the steel interface, and the thickness of reaction layer could be predicted during laser brazing (thermal cycle) process based on the growth kinetics with the additivity rule. The metal flow analysis of the melted filler metal on joints revealed that wettability and spreadability of the filler metal on GI steel joint were superior to those on GA steel joint. The fracture strength of lap joint attained approx. 55-75% of the base metal strength of aluminum alloy. It was concluded that fluxless laser brazing could be successfully performed by using tandem beam because the zinc coat layer acted as brazing flux.