Solderability of AZ31B Magnesium Alloy Coated by Copper and Strength of the Solder Joints

摘要

Magnesium alloys are promising as light materials, while their high chemical reactivity makes them difficult to be soldered. In this study, the AZ31B alloy was pretreated by zincification and coated by an electrodeposited Cu layer, and then soldered with Sn-58Bi solder in air furnace. The microstructure and properties of the AZ31B/Cu(Zn)/SnBi solder joints were characterized to evaluate the solderability of the Cu-coated Mg alloy and the influence of soldering on the Cu coating. It was found that the Cu coating is dense, and little defect exists along the Cu(Zn)/AZ31B interface. The soldering process has little negative effect on the bonding between the Cu coating and the AZ31B substrate, and the AZ31B/Cu(Zn)/SnBi solder joints of high metallurgical quality were obtained. Tensile fracture of the solder joint occurs mainly in the solder, with no peeling of the Cu coating. Under shear loading, cracks initiate inside the SnBi solder and the final fracture of the joint occurs around the Cu6Sn5/solder interface or along the Cu(Zn)/AZ31B interface. The tensile and shear strength of the AZ31B/Cu(Zn)/SnBi solder joints are close to that of the SnBi/Cu solder joints. It is demonstrated that the Cu-coated Mg alloy shows superior solderability and can be soldered by the Sn-based low-melting solder in air.