Study on laser brazing characteristics of dissimilar metals

Laser brazing between commercially Al coated steel and type Mg alloy(AZ31B) has been carried out in the Mg-based and Al-based insert metals. The brazing bonds have been evaluated using light microscopy, electron probe microanalysis (EPMA), X-ray diffraction (XRD) technique and tensile shear testing. Light microscopy shows that different intermediate layers are formed in the reaction zone, and these layers changes with a kind of insert metals. EPMA revealed that, at any particular insert metal, Mg-rich phases (intermetallic phases) formed in cell boundary of the Mg alloy side, but original coated layer remained in the steel side. This microanalysis also indicated different step formations in the concentration profile of Al, Mg, Zn and Si over different composition ranges in the fusion zone indicating formation of intermetallic phases that were detected by XRD. Brittle intermetallic phases lower the strength and ductility of the brazed couples significantly. Best room temperature tensile shear fracture load, approximately 520kg. has been obtained at Mg-6.5Al-1Zn-0.3Mn due to minimal deleterious effects.