Effect of surface roughness on the performances of laser-welded Invar 36 alloy joints

Abstract

An experimental study was carried out to investigate the effect of surface roughness on the performances of laser-welded Invar 36 alloy joints. Four surface roughness levels from 0.12 μm to 2.84 μm were obtained by pneumatic driven shot peening. The morphology, pores, microstructure, microhardness, and mechanical properties of weld joints with a thickness of 9 mm were studied for different surface roughnesses. Results show that the increase of surface roughness can significantly improve weld penetration due to an increase in laser absorptivity. But it also results in coarse grains and joint softening. For smooth surfaces, the generation of porosity was almost unavoidable when heat input was large, but rough surfaces with an appropriate surface roughness (e.g. 2.14 μm) can effectively eliminate weld porosity and obtain defect-free joints. Besides, when the surface roughness was 2.14 μm, the mechanical properties of the joint were also the most ideal: tensile strength and impact energy of the joint reached 439.4 MPa and 78.39 J (99.6 % and 88.6 % that of the base metal), respectively, and the elongation reached 33.3 %. These metrics were significantly better than previously reported results, which suggests the effectiveness of proper surface roughness to improve laser-welded joint performances.