Effect of Zn interlayer on brazeability of AZ31B–Mg alloy to steel sheet

The brazeability of AZ31B-H24 magnesium alloy sheet to Zn electroplated, plain carbon steel sheet using an Mg-Al-Zn alloy filler metal and a diode laser heat source has been investigated. While the Zn coating promoted good wetting between the molten filler alloy and the steel sheet, it did not play a direct role in forming the final bond. Bonding between the magnesium alloy and the steel was facilitated by the formation of two transition layers. First, a nanoscale layer of FeAl3 phase formed on the surface of the steel by diffusion of Al from the Mg-Al-Zn brazing alloy into the steel. Upon further cooling, nucleation and growth of either alpha-Mg+MgZn eutectic phases or Mg-2(Al,Zn)(3) phase occurred on the FeAl3 surface layer.