Effect of weld microstructure on the static and impact performance of resistance spot welded (RSW) dual phase steels

Evaluating the impact performance of resistance spot welded (RSW) joints in advanced high strength steels (AHSS) is critical for their continued integration into the automotive architecture. The effect of strain rate on the joint strength and failure mode is an important consideration in the design of welded structures. Recent results suggest that the failure mode is dependent upon the strength, chemistry, and processing of AHSS. The current study details the relationship between the joint microstructure and impact performance of spot welded DP600 and DP780, which are commonly used in the automotive architecture. Static and impact tests were conducted using a universal tensile tester and an instrumented drop tower, respectively. Microstructure of the various weld regions are detailed and compared. In addition, Results for elongation, failure load and energy absorption for each material are presented. Failure modes were detailed by observing weld fracture surfaces. Correlations between the fracture path and mechanical properties were developed using observed microstructures in the fusion zone and heataffected-zone. Results showed that good impact performance was obtained in DP780 compared to the DP600. Copyright © 2007 MS&T'07®.