Effect of process paths on residual stress of multi-layer and multi-pass laser cladding

Residual stresses of multi-layer laser cladding Co-based coating on Q345 steel surface are measured by blind hole method, and the influence of laser cladding process paths on residual stress of each laser cladding layer is studied. The test results show that the residual stress along the laser cladding scanning direction is much larger than the stress in the vertical direction of the weld bead, and both are tensile stresses. The residual stress of the laser cladding coating increases obviously with the increase of the thickness of the single cladding layer. The residual stress increases by nearly 40% since the thickness of single cladding layer increases from 0.6 mm to 1 mm. Compared with the residual stress in the case where the two cladding layers are in the same scanning direction, the residual stress of coating decreases obviously when the overlaying sequence of two layers of cladding layer is perpendicularly crossed. And the lowest residual stress can be obtained when the surface of the test plate is cladded in zones and the multi-layer cladding layer in each zone are vertically cross-surfacing. A certain pre-deformation of the test plate before cladding has little effect on the final residual stress of the coating, but significantly reduces the residual stress on the back of the test plate.