Study On Microstructure And Properties Of CMT Arc Additive Brass Repair Layer

Due to friction wear and seawater erosion,copper alloy parts fail due to lack of size,and the replacement of parts to maintain operation and improper handling of scrap parts will cause a huge waste of resources.To improve the material utilization rate and achieve the improvement of the size repair and performance of damaged brass alloy parts,the nickel-aluminum bronze alloy was made on the surface of C35300 brass matrix by using cold metal transition（CMT）technology.In order to obtain the best material addition process parameters and obtain the comprehensive excellent repair layer,the influence of different arc adding process parameters on the macroscopic morphology,microstructure and hardness of single layer cladding layer was studied.At the same time,the influence of interlayer temperature on the dimensional accuracy,microstructure,tensile properties and corrosion resistance of multi-layer single-channel straight wall was studied,the following conclusions were reached:（1）Experimental results show that the macroscopic size of single layer Ni-Al bronze cladding layer made by CMT arc material is closely related to the thermal input,while the wire feeding speed,welding speed and welding wire tilt angle process parameters all affect the thermal input during welding.The wire feeding speed and wire tilt angle are positively correlated with the thermal input value.（2）At room temperature,the internal microstructure of the cladding layer is composed ofα-Cu matrix,residualβphase（martensite phase）,Pb phase,κ_Ⅰ,κ_Ⅱ,κ_Ⅲandκ_Ⅳphase.With the distance from the substrate,the content ofβphase first increases and then decreases.The internal microstructure of the cladding layer presents an obvious gradient structure.From the fusion line of the bonding zone to the top,the cladding layer presents fine cell crystals,columnar crystals growing along the direction of reverse heat flow,dendritic and equiaxed grains with large grain size and disordered growth direction.The grain size increases with the increase of heat input.The average hardness of the cladding layer is 185.6 HV_0.5,which is better than that of the brass substrate 123.9 HV_0.5,and the hardness of the cladding layer adjacent to the substrate increases obviously,up to 206.6 HV_0.5.According to the comprehensive analysis of macroscopic morphology and microstructure,the optimal process parameters of CMT additive single-layer Ni-Al bronze are as follows:wire feeding speed 9.0 m·min^-1,welding speed 6.0 mm·s^-1.（3）As the temperature increases,the surface roughness of the straight wall increases gradually,reduced dimensional accuracy,at an interlayer temperature of 300℃,straight wall of each layer of dislocation,overflow stay phenomenon.CMT the microstructure of Ni-Al-Bronze wall with arc-adding shows dendrite,equiaxed crystal,columnar crystal and dendrite circulation,and the dendrite size gradually fluctuates and increases;with the increase of interlayer temperature,the microstructure size of straight wall increases gradually.The Vickers hardness values in the straight wall range from 155 HV_0.5 to 185 HV_0.5 and show a decreasing trend with the increase of the distance between the straight wall and the substrate.The average microhardness of Ni-Al bronze straight wall is 2.40 GPa,which is 1.57 times higher than that of the matrix,and the average elastic modulus is 122.79 GPa,which is 1.99 times higher than that of the matrix.The interlayer temperature has no obvious effect on the internal microhardness of Ni-Al bronze.The tensile strength of the straight wall in the welding direction and 45°inclined direction is about 570 MPa,which is much higher than that in the stacking direction.The elongation of the straight wall in the stacking direction,welding direction and 45°inclined direction is 41.14%,54.00%and 41.04%,respectively,and the elongation value in the welding direction is the highest.The corrosion resistance of Ni-Al bronze straight wall is better than that of matrix.