Abstract
This study is to investigate the microstructure and the mechanical properties (hardness, strength, fatigue resistance) of laser welded double-lap joints from two different steels, ultra-high strength abrasion resistant steel (AR400) and low strength structural (S355 MC) steels. The laser welding was conducted at two different energy density 170 and 958 J/mm2 and constant power 3 kW. The morphology and the microstructure of the cross-section lap joints have examined by optical microscopy. The shear strength and the fatigue resistance of the double-lap joints were evaluated by uniaxial tensile tests and fully reversed tension–compression strain-controlled fatigue tests, respectively. Whereas the hardness of the welded lap joints of UHS steel has been decreased due to the tempered martensite formation. The microstructure of the laser welded lap joints of LS steel shows martensite formation in the fusion zone. Hence, the hardness has been significantly increased to 300 Hv. The shear strengths of the welded lap joints have significantly influenced by the laser power density. Significant improvement in the strength could be observed in the strength of the lap joints of UHS steel at energy density 958 J/mm2. Fatigue cracking along steels sheets boundaries that intersect the weld zone in the welded lap joints and the crack propagation towards the weld zone observed to be the fatigue-induced microstructural features in the lap joints welded by laser.
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