Laser Welding of Advanced High Strength Steels for Tailor Welded Blank (TWB) Applications

One of the most popular weight reduction strategies in auto bodies is usage of tailor welded blanks (TWB). TWBs with high-strength low-alloy steels and advanced high-strength steels (AHSS) offer possibility of significant weight reduction. In the present work laser welding studies were carried out to fabricate TWB's involving 1.6 mm thickness AHSS DP 590 (dual phase steel) and 0.8 mm thickness conventional IF (interstitial free) steel in different combinations and characterized for their metallurgical and formability characteristics. Fusion zone microhardness was varying with change in material combination. While DP590-DP590 and IF-IF have shown fusion hardness of 300-350HV and 150-180HV, respectively, the dissimilar DP590-IF showed a fusion zone hardness of 250-330HV.Beam offsetting towards the thinner side has reduced the peak hardness. Microstructural analysis revealed mixture of martensite and refined ferrite in the fusion zone of dissimilar welds. The erichsen cup height for TWBs (11 mm) was between cup heights of the welded coupons of the two base metals DP590 (9.5-10 mm) and IF (13.5-14 mm), respectively. Limiting Dome height tests also revealed a similar observation that the limit strains of the TWBs are between the limit strains of the two base materials.