Effects of Interlayer Thickness on Dissimilar Joining between Aluminum Alloy and Magnesium Alloy using Laser Brazing

Abstract

　The effects of Ti interlayer thickness on the dissimilar metals laser brazing between A5052 aluminum alloy and AZ31 magnesium alloy were investigated. The traveling velocity (V_f) to wire feeding speed (V_w) laser brazing ratio that produces good bead appearance was determined to fall within the 3-5 range. Regardless of the thickness of the interlayer, it was found that joining was possible at a Ti/A5052 interface temperature of 800℃ or higher, and that burn-through occurred when the Ti/A5052 interface temperature exceeded approximately 1060℃. The reaction layer thickness at the Ti/A5052 interface increased as the interlayer thickness decreased and as the laser power increased. Joining becomes possible when the reaction layer thickness is 1 μm or higher. Furthermore, fracture occurred in the base material of all joints produced with a laser power of 900 W, regardless of the interlayer thickness, and the material's measured strength was 80% or more of the A5052 base material strength of 235 MPa. It was found that fracturing at the Ti/A5052 interface of the joint occurred at the laser power of 800 W or lower, and brazed filler metal fracture occurred at the laser power of 1000 W or higher. It is considered that the filler metal fracture of the joint results from the propagation of individual cracks in the Mg₁₇Al₁₂ within the filler metal, which are caused by tensile deformation. The amount of Mg₁₇Al₁₂ in the filler metal of the joint increases as the laser power increases, and is 20% or higher of the total filler area when the filler metal of the joint breaks.