Process,Microstructure And Properties Of Metal Thin-walled Structure By Laser Additive Manufacturing

Metal thin-walled parts are widely used because of their advantages of light weight,material saving and high precision.Laser additive manufacturing technology is an advanced technology that uses laser as a heat source to melt metal materials and fabricate solid parts by layer-by-layer,it can realize moldless,fast,full dense near-net forming of highperformance and complex structural metal parts and has significant advantages in thin walls processing.In this paper,the influence of process parameters on the quality of single-clad cladding and the forming process of thin-walled structures such as straight-walled structures,inclined structures,rotating structures,and intersecting structures were studied.The effects of laser power,scanning speed and powder feed rate on the geometry of the cladding layer were studied via systemly process experiment,and optimized parameter window of cladding layer was obtained.The interactions between powder and laser,powder and molten pool were analyzed,during the cladding process,the spot diameter is smaller than the spot diameter and the spot coincides with the center of the spot should be ensured.The ideal single track morphology required for the thin-walled part was obtained,with the cladding layer width W = 2.29 mm,height H = 0.79 mm.In the additive manufacturing process of the straight wall structure,the collapse of both ends of the thin-walled structure was solved when the defocusing amount of the powder is suitable,and the wall thickness accuracy is 2.3±0.1mm.The extreme tilt angle of the inclined thin-walled structure is 35.06° under the single-pass process parameters used in this paper.A random starting-point scanning path for cladding was adopted during the rotating thin-walled structure forming process,and the surface of the cylindrical structure is smooth and without undulating.For the intersecting thin-walled structure with a inflection,protrusion in the inflection point of the thin wall was no obvious when using an arc transition with an appropriate radius.The thin-walled structures of straight line intersects with a straight line and a circular arc was preferably formed with a suitable lateral offset.As for arc and arc tangent thin-walled structure,metallurgical bonding is formed at the arc tangent when the overlap ratio is 0%,and the height difference between arc tangent and circular arc contour is minimum.The decussation structure with good forming quality is obtained through process controlling.A white-white fusion zone appeared in the fusion zone between the thin-walled cladding layer and the matrix,and the planar region was formed on the upper part of the fusion zone.Microstructure of the thin-walled structure is mainly epitaxial growing dendrites while the top is the equiaxed grain,and the dendrites near the substrate are more coarser.Hardness of the thin-walled structure is higher than the substrate,and the hardness near the substrate is lower.Tensile and yield strength are significantly higher than the traditional forged 304 stainless steel.The tensile strength and the yield strength of the specimen parallel to the scanning direction are higher than the vertical scanning direction,and the elongation is opposite.