Effect of laser welding mode on the microstructure and mechanical performance of dissimilar laser spot welds between low carbon and austenitic stainless steels
This paper aims at investigating metallurgical and mechanical characterization of dissimilar laser spot welds between low carbon and austenitic stainless steel sheets. Microstructural examination, microhardness test and quasi-static tensile–shear test were performed. Mechanical properties of the welds were described in terms of peak load. The effects of laser mean power on the performance of dissimilar laser spot welds have been studied. It was found that increasing laser mean power leads to the transition of laser welding mode from conduction to keyhole. This transition causes a significant growth of the fusion zone size in the lower sheet, i.e. the low carbon steel sheet; since, the keyhole acts as an effective trap for the laser beam and will greatly increase the energy absorption from the incident laser beam. It is also shown that the fusion zone size in the weaker sheet, i.e. the low carbon steel sheet
In this research, laser spot welding of low carbon to austenitic stainless steel sheets was studied. Effect of the increasing laser mean power on the shape, dimension and structure of the weld fusion zone was investigated. The mechanical performance of dissimilar laser spot welded joints was analyzed under lap-shear loading. The following conclusions can be drawn from this research (1) Laser spot welding is a very successful process for joining austenitic stainless steel and low carbon steel in an overlapped configuration (2) The fusion zone has an asymmetric shape in dissimilar LSW between low carbon steel and austenitic stainless steel because of the one-side nature of the laser welding process in addition to the different laser beam absorption and the thermal onductivity of the base metals
(3) Transition of the laser welding mode from conduction to
keyhole welding via increasing the laser mean power significantly affects the fusion zone size in the lower (CS) sheet
and in view of that the dilution between two base metals
strongly depends on the laser welding mode.
(4) Increasing the laser mean power leads to an increase in the
load carrying capacity of the LSW primarily due to the
increasing fusion zone size in the CS sheet. Larger volume
of the high strength weld metal in the CS sheet lessens the
rotation of the weld ring and therefore delays the strains
concentration in the base materials around the weld ring
and the subsequent necking..
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