Research On Fiber-MAG Hybrid Welding Of Low-Alloy Ultra High Strength Steel

D406A is a kind of low-alloy ultra high strength steel, which is independentlyresearched by our country and widely used in aerospace field. Because of its complicatedchemical composition, D406A owns good mechanical properties, but the welding processof D406A has become relatively complicated.Fiber laser–MAG hybrid welding technology collects the advantages of laser weldingand arc welding together. One side welding double forming can be achieved by thistechnology. Compared with laser welding, Fiber laser–MAG hybrid welding hasovercome the disadvantages of harsh installation accuracy. In this paper, a large quantityof experiments on fiber laser–MAG hybrid welding of10mm thick mild steel has beenresearched, forming a systematic process database about fiber laser-arc hybrid welding of10mm thick mild steel. Under the condition of other parameters constant, welding plasmaform of laser-arc hybrid welding was researched by CCD high speed camera. Weld shapewas more perfect under the condition of arc leading laser-arc hybrid welding. The power-penetration speed curve was achieved by performing deep penetration laser weldingexperiment. After analysis of the heat input to the influence of the weld, heat input shouldbe controlled in less than60000J/m. With the increasing of laser-arc distance, theinteraction between the two heat sources was reduced. Laser-arc distance effects on weldpenetrate more than width. The larger penetration can be obtained under the condition ofnegative defocusing distance but it can cause more plasma shielding in too much negativedefocusing distance and decreases penetration. The best range of fit-up gap was between0.5and0.7mm.On the basis of basic experiment, the parameters of laser-arc welding10mm thickD406A were optimized. Welding current was280A, laser output power was4.2kW,welding speed was1m/min, welding voltage was28V, the proper gap-up range was0.5to0.7mm, dry elongation was15.0mm, wire feed speed was3.0mm, shielding gas wasAr80%+CO₂20%25l/min, defocusing distance was-2.0mm. And then mechanical properties test of the welding bead was performed, the largest tensile strength was1670MPa, extension rate was20.83%. The fracture surface of welding bead is belongingto dimple fracture after analysis of SEM analysis. Through metallographic analysis, SEManalysis and hardness test, the welding microstructure characteristic was analyzed.Welding bead was divided into laser weld area, laser-arc composite area and arc area.Microstructure of the three areas was uniformity. Depending on the hardness test, thehardest area appeared in the HAZ area.