Study on fibre laser spot welding of TRIP980 steel

Abstract

A 980 MPa transformation induced plasticity (TRIP) steel was fibre laser spot welded by different Argon (Ar) shielding conditions, laser power (1000 up to 2500 W) and defocusing distances (28 up to z8 mm). The surface appearance, cross-section macrostructure, microstructure, hardness, tensile shear properties and fatigue properties of laser spot welds were evaluated. The results showed that the welds with Ar shielding had larger weld appearance and bonding sizes, better tensile shear properties compared with the welds without Ar shielding. With the increase in laser power, the laser welding mode changed from conduction to keyhole, which improved the bonding size and mechanical properties. The bonding size and mechanical properties increased in the order of defocusing distances of z8, 28, z4, 24 and 0 mm. During the fatigue tests of laser spot weld, the fusion zone pullout and sheet transverse fracture failure modes were observed.

Effects of welding parameters on fibre laser lap weldability of galvanised DP1000 steel

“…The bonding size between the sheets was measured using these photographs with the help of an image analyser coupled to the microscope. 15 The microhardness profiles across the investigated laser lap welds were determined using a Vickers hardness tester. The hardness values were measured along the centrelines of the upper and lower sheets at a regular interval of 0.15 mm in the transverse direction of the cross-section.…”

“…The hardness values were measured along the centrelines of the upper and lower sheets at a regular interval of 0.15 mm in the transverse direction of the cross-section. Measurement of hardness was carried out using a load of 100 g with indentation duration of 15 s. 15 Tensile shear tests were used to characterise the mechanical properties of laser spot welds. Figure 1 shows the sample dimensions.…”

“…The laser welding head was kept perpendicular to the workpiece surface during the experiments. 15 In this experiment, the DP1000 steel sheets were lapped and clamped with different joint gaps between upper and lower sheets. The laser welding was conducted from the upper surface of the lapped joints.…”

“…The bonding size between the sheets was measured using these photographs with the help of an image analyser coupled to the microscope. 15…”

“…The effects of joint gap on the bonding size and macrostructure of the welds are shown in Figs. 5d and 7 (samples [13][14][15][16][17][18]. With the increase of the gap, the bonding size first increases and then decreases.…”