Dissimilar resistance spot welding of aluminum to magnesium with Zn-coated steel interlayers

Resistance spot welding of AZ31B Mg alloy to AI Alloy S754 was studied using Zn foil and Zn-coated steel interlayers. Mechanical properties and microstructure of the welds were analyzed. The strength requirements of AWS Standard D17.2 could not be met when a Zn foil interlayer was used. However, acceptable joint strengths were achieved using a Zn-coated steel interlayer, since the steel remains solid and can successfully keep AI and Mg from mixing. An ultrathin Fe-Al layer present at the Zn-coating interface of the steel interlayer promoted metallurgical bonding at both AI and Mg alloy interfaces. Welds made with Zn-coated steel interlayers met the strength requirements of the AWS standard and reached 74% of the strength of comparable AZ31B similar resistance spot welds.