Improved Weldability for Laser Welding Press-Hardened Steel via Thinning Coatings: Part 1 — Microstructure Characterization and Mechanical Testing

As integrated door rings with high safety are being used for automotive applications, Al-Si-coated press-hardened steel (PHS) is attracting wider attention. However, during laser welding of thickly coated (~30 μm) PHS, excessive ferrite is formed in the weld, so it is necessary to use a filler metal to limit this issue. This work investigated the laser weldability of thinly (~16 μm) and extra-thinly (~10μm) coated PHSs using a low-cost C-Mn filler wire at weld travel speeds of 3–7 m/min. The results indicated that laser welding of PHSs with thinner coatings exhibited better weldability due to a lower volume fraction of ferrite in the weld. However, the thinly coated PHS joint welded at 7 m/min failed at the Al-enriched weld toe, where strip-like ferrite was observed. Al enrichment originated from the coating outside the weld, and the extent of Al enrichment was closely related to the high welding speed.