Weld Growth Mechanism, Microstructure, and Mechanical Properties of Resistance‐Spot‐Welded Joint of R60702 Zirconium‐Alloy Triple Sheets

Abstract

In this study, triple sheets of R60702 zirconium (Zr) alloy are joined together using the resistance‐spot‐welding process. The nugget formation mechanism and microstructure of the weld joint in three equal‐thickness sheets of R60702 Zr alloy are studied. In the results, it is revealed that the initial nugget forms at the top of the intermediate sheet, and subsequently expands both radially and axially until a complete nugget is formed. The fusion zone (FZ) exhibits a martensitic microstructure, while the heat‐affected zone (HAZ) consists of two regions: coarse‐grain HAZ and fine‐grain HAZ. The hardness in the FZ is higher than that of the HAZ and the base metal. Furthermore, the tensile‐shear force and fracture mode of the weld nuggets are also studied. The weld joints exhibit a maximum tensile‐shear load of 5.7 kN under the following welding parameters: welding current of 14 kA, welding time of 150 ms, and welding force of 3.6 kN. Three failure modes are identified interface fracture, partial button fracture, and button fracture.