Influence of scanning speed and defocus distance on laser welded PA6GF30/SUS444 dissimilar lap joints

•The weld seam of PA6GF30/SUS444 lap joint by laser welding was composed of melted zone and glass transition zone.•The tensile-shear force of the joint can be determined by the undecomposed zone width in the melted zone.•Mechanical anchorage and chemical bonding were the key factors for the joining of PA6GF30 and SUS444. Lap joints of polyamide 6 reinforced with 30 wt.% glass fiber (PA6GF30) and SUS444 ferritic stainless steel dissimilar materials were fabricated by laser welding, and the influence of scanning speed and defocus distance on the interfacial joining was investigated. The weld seam was composed of melted zone and glass transition zone, and the temperature field simulation results of the joint interface illustrated that the melted zone consisted of undecomposed and decomposed zones of PA6GF30. The tensile-shear force decreased from 1695.7 N to 1192.5 N when the scanning speed increased from 8 mm/s to 12 mm/s, and that increased from 1554.5 N to 1785.9 N as the defocus distance increased from 44 mm to 61 mm. The variation tendency of the undecomposed zone width in the melted zone was consistent with that of the tensile-shear force of the lap joints. The interfacial observation displayed that a mechanical bonding was formed at the joint interface because the melted resin filled in the grooves on the surface of SUS444. In addition, a new chemical bonding identified as Cr-O-C was generated in the interface.