Resistance spot welding of DH1200 using short pulses and high currents: Effects on nugget size, microstructure, hardness, liquid metal embrittlement, and tensile shear strength

This study investigates short-pulse high-current resistance spot welding (RSW) of DH1200, a third-generation advanced high-strength steel (AHSS) critical to lightweight automotive structures. Six RSW scenarios were designed by varying weld time and current in both single- and double-pulse schedules, targeting a rarely explored regime with durations as short as ∼100 ms and currents up to 15 kA. Key weld attributes, including nugget size, microstructure, hardness, liquid metal embrittlement (LME) cracking, and tensile shear strength (TSS), were systematically analyzed. Contrary to conventional understanding, increased heat input did not necessarily generate larger nuggets or greater LME severity. Instead, weld current was found to be the dominant controller of nugget size, LME cracks, and TSS. Microhardness near the weld centerline was governed primarily by microstructure and remained largely insensitive to process parameters. Short-time, high-current conditions in double-pulse RSW produced large nugget sizes, exceeding even the criterion, and enhanced both TSS peak load and energy absorption. Furthermore, reducing weld time at constant current significantly mitigated LME, which caused substantial strength degradation in two severe cracking cases. These findings offer new insights into the development of short-pulse RSW schedules beyond conventional practice, enabling cycle-time reduction in automotive production. • Nugget size dropped significantly at shorter times under fixed current. • Microhardness profiles remained largely unaffected by weld time or current. • More heat input didn’t necessarily increase nugget or intensify LME. • Shorter weld times could mitigate LME cracks. • LME cracks severely degraded weld shear strength.