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

Abstract

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 α-Mg+MgZn eutectic phases or Mg₂(Al,Zn)₃ phase occurred on the FeAl₃ surface layer.

Keywords:

• Laser brazing
• AZ31B Mg sheet
• Zn coated steel sheet
• Microstructure

Acknowledgements

The authors wish to acknowledge support of the American Welding Society Graduate Fellowship programme and the Magnesium Network of Canada (MagNET) supported by the Natural Sciences and Engineering Research Council of Canada for sponsoring this work.