Influence of energy ratio on microstructure and mechanical properties in the transition zone of hybrid laser-MIG welded AH36/316L dissimilar joints

The present study investigated the influence of energy ratio on microstructure and mechanical properties in the transition zone of hybrid laser-MIG welded 316L/AH36 joints. The region between the laser zone and hybrid zone was defined as the transition zone. The ratio of laser to arc energy was defined as energy ratio. Similar microstructure types including ferrite, austenite, and martensite were observed in the transition zone under each energy ratio. However, obvious difference in microstructure distribution and crystallographic characteristic in transition zone was found in varying energy ratio. With the energy ratio decreasing from 2:1 to 1:2, the fraction of martensite was decreased from 83.1% to 65.6%, the fraction of high angle grain boundaries was increased from 44.8% to 61.3% and the average grain size was increased from 3.62 to 17.20 μm. The phenomenon was attributed to the improvement of cooling rate and reduction of filler metal. Therefore, the highest average microhardness value of 445 HV in the fusion zone was obtained under the highest energy ratio compared to that of 223 HV under the lowest energy ratio. Besides, the low-temperature impact absorption energy was increased from 41 to 90 J and the tensile fracture mode was changed from cleavage fracture mode to ductile fracture mode as the energy ratio decreased from 2:1 to 1:2.