Research On Mechanical Constraint Assisted Underwater Wet Arc Additive Repair Process

In recent years,China has paid more and more attention to marine resources,and the number of marine engineering structures is increasing.Therefore,the restoration of underwater structures is becoming more and more important.In view of the problems of poor arc stability,microstructure hardening and size limitation of repair structure in the actual repair work of underwater wet welding technology,this paper proposes a mechanical constrain-assisted underwater wet arc additive repair method.The evolution behavior of arc bubbles is controlled by auxiliary device to improve arc stability during repair process.At the same time,through the multi-layer additive process to improve the repair layer structure,finally achieve the purpose of improving the quality of underwater repair and expanding the scope of repair.Firstly,the evolution behavior of arc bubbles in the multi-layer additive process and the bead-on-plate process under different conditions was compared and investigated.Based on this research,a mechanical restraint device with holes was designed on the basis of a mechanical restraint device without holes.The results show that the arc stability of the two processes with the assistance of non-porous mechanical constraints is significantly improved compared with that without device,but the arc bubble evolution behavior in the multi-layer additive process is more unstable than that in the bead-on-plate process,so the arc stability is worse.In order to solve this problem,a mechanical constraint device with holes was designed based on controlling the evolution behavior of arc bubbles in multi-layer additive process.Based on the mechanical constraint device without holes,the arc stability was further improved.The results show that the reciprocal sum of the coefficient of variation of voltage and current in the multi-layer additive process with mechanical constraint device with holes assistance increases by 20%,and the proportion of unstable combustion process decreases by 67%,compared with the non-porous mechanical constraint assistance,thus achieving higher arc stability in the underwater wet arc additive repair process.Then the influence of technological parameters on the formation of deposition layer and arc stability during deposition is studied.The results show that with the increase of welding voltage,the width and height of the deposition layer increase gradually,and the arc stability firstly increases and then decreases.The arc stability is the best when the welding voltage is 32 V.With the increase of wire feeding speed,the width and height of the deposition layer increase gradually,and the arc stability first increases and then decreases.The arc stability is the best when the wire feeding speed is 8.5m/min.With the increase of welding speed,the width and height of the deposition layer decrease gradually,and the arc stability first increases and then decreases.The arc stability is the best when the welding speed is 2.5mm/s.Finally,the microstructure and mechanical properties of the repaired deposition layer were investigated with the sample of the additive wall.The results show that the thermal effect of the multi-layer additive process is beneficial to improve the plasticity of the repaired deposition layer.The microstructure of the repaired deposition layer is mainly polygonal ferrite,and the microstructure of the heat-affected zone of the base metal is mainly tempered martensite.The thermal effects of the subsequent deposition layer on the previous deposition layer are similar to the normalizing on nearby area and tempering on distant area.The thermal effect of the second deposition layer on the heataffected zone of the base metal is similar to the low temperature tempering effect,which reduces the maximum hardness of this zone from 309 HV to 216 HV.The longitudinal tensile strength of the additive wall is 433 MPa,which reaches 78.3% of the actual tensile strength of the base metal.The elongation is 10.8%,reaching 95.6% of the actual elongation of the base metal.The tensile fracture of the additive wall is a typical ductile fracture,and the fracture morphology is mainly dimple.At last,a simulated repair test was carried out.The plates with a spacing of 20 mm were successfully connected by the additive repair method in the water environment,which proved that the method was feasible and could realize the repair of a larger structure.