Laser Weldability of Dual Phase Steels in Tailored Blank Applications

Advanced, high strength dual phase steels are used with increasing frequency in automotive applications requiring high energy absorption for enhancing crashworthiness, reducing mass, or both. Automotive designers are interested in utilizing high strength dual phase steels for tailored blanks but often lack the resources for fully evaluating material formability, fatigue performance and laser welding technology. This study investigates the feasibility of manufacturing tailored blanks with dual phase (DP) steels, manufactured in North America and Japan, of ultimate tensile strengths up to 1000 MPa. A commercial Soudronic LPQ 2200 laser welder at ProCoil Corporation was used for joining the high strength steel blanks as a global benchmark of tailored blank welding technology.

Laser butt welds in cold rolled and hot dip galvannealed 590,780 and 980 MPa ultimate tensile strength (UTS) DP steels were evaluated in a variety of mechanical property and formability tests. These included tensile tests, dome tests and fatigue (tension-zero and reversed bending) tests. This study also evaluated several macro-structures and microstructures of weld metal and heat affected zones (HAZ) from hot dip galvannealed 590, 780 and 980 UTS high strength DP steels.