STUDY ON LASER BRAZING CHARACTERISTICS OF DISSIMILAR METALS

摘要

Laser brazing between commercially Al coated steelrnand type Mg alloy(AZ31B) has been carried out in thernMg-based and Al-based insert metals. The brazingrnbonds have been evaluated using light microscopy,rnelectron probe microanalysis (EPMA), X-rayrndiffraction (XRD) technique and tensile shear testing.rnLight microscopy shows that different intermediaternlayers are formed in the reaction zone, and these layersrnchanges with a kind of insert metals.rnEPMA revealed that, at any particular insert metal,rnMg-rich phases (intermetallic phases) formed in cellrnboundary of the Mg alloy side, but original coatedrnlayer remained in the steel side. This microanalysisrnalso indicated different step formations in thernconcentration profile of Al, Mg, Zn and Si overrndifferent composition ranges in the fusion zonernindicating formation of intermetallic phases that wererndetected by XRD. Brittle intermetallic phases lowerrnthe strength and ductility of the brazed couplesrnsignificantly.rnBest room temperature tensile shear fracture load,rnapproximately 520kg. has been obtained at Mg-6.5Al-rn1Zn-0.3Mn due to minimal deleterious effects.