Weldability of 440 MPa galvanized steel with inverter DC resistance spot welding process

Purpose: This paper comparatively analyzes resistance spot weldability depending on whether or not 440 MPa-grade steel is galvanized at inverter DC spot welding. Design/methodology/approach: To compare the resistance spot weldability depending on whether or not the steel is galvanized, an inverter DC welding system was designed. Then, using this system, both tensile strength testing and macro-section testing were conducted on SPRC440 (uncoated steel) and SGARC440 (galvanized steel), and weldability was evaluated. Suitable welding conditions were calculated using the resistance spot welding variables such as electrode force, welding time and lobe diagram on the welding current. The low limit of the lobe diagram was set to the low limit of the tensile strength of 440 MPa-grade steel while the high limit was set depending on whether or not expulsion was detected. Findings: Compared to uncoated steel, galvanized steel had lower suitable welding current conditions and a narrower lobe diagram. Research limitations/implications: This paper compared resistance spot weldability and lobe diagram depending on whether or not 440 MPa-grade steel is galvanized. Practical implications: This paper confirms the weldability of galvanized steel by comparing resistance spot weldability depending on whether or not steel is galvanized. Originality/value: For analysis of resistance spot weldability depending on whether or not steel is galvanized, weldability was compared between SPRC440 (uncoated steel) and SGARC440 (galvanized steel) under the same welding conditions. As a result, compared to uncoated steel, galvanized steel had lower suitable welding current conditions and a narrower lobe diagram.