Characteristics Of Medium Thickness Of Titanium Plate Laser-MAG Hybrid Welding

Titanium alloy is famous for its excellent overall performance and plays asignificant role in aerospace structures. The plate titanium alloy laser-MIG weldingprocess and analysis through the weld microstructure is studied, the relationshipbetween mechanical properties and organization was explored.Firstly, the transfer behavior of molten drop was researched. With the increasing oflaser power, the transfer frequency of the globular fDis changed, and the distancebetween globular and laser beam DL-Dis also changed. When it is3Kw, fDtends to bemaximum, and DL-Dtends to be minimum. With the increasing of laser-arc distance, thetransfer frequency increases significantly. When the current of MIG climbs to190A, thetransfer mode turns from big drops to shoot drops; voltage impedes globular transfer,when the voltage exceeds26V, it causes the droplet fail to transfer properly; shieldinggas flows18L/min when the globular transfer axial and stability of transfer are to thebest.The orthogonal test found that in the weld bevel angle of the sample has animportant impact on the backing weld process： the tensile strength is maximum whenbevel angle reaches60°under the same parameters; the weld width and depth of fusionmaximize when melting maximum the bevel angle is90°. As to double-side-welding15mm thick plate, the best practice is to weld2layers on one side before flipping overto weld the other2ones. In roughly the same amount of heat input, the more weldinglayers, the less weld width and heat affect the zone width.Microscopic characteristics of weld bead: part of the area has a large aspect ratio,long and straight α ’martensite ordered, widmanstatten cluster was formed in the shape;other portion has small size, small aspect ratio α’ horse s body, interwoven basket-liketissue formation. Microscopic characteristics of narrow tissue:’martensite morphologyof coarse α elongate lath and needle; between martensite grains exist α-β tissueconsisting of α+β+transition in memory of martensite crystal dislocation structure;residual β.Next, the paper studied the grain growth and structural transfer of the weld zone ofTC4titanium alloy laser-MIG welding under different heat input conditions. Studyshows that the weld zone of TC4titanium is Alpha′martensite mixed with lath andacicular martensite, and within the crystal dislocation and a small amount twin crystals.With the increase of the welding heat input, average width of Alpha′martensite lathincreases from0.49um to0.82um and the dislocation density increases. α-β lamellamicrostructure by the stripes into continuous shape. Finally, interlayer microstructure of multi-layer welding was researched. Inremelting zone, the growth direction of the grains is randomly omnidirectional, thegrain size is relatively small, and the thickness of α′+βsheet in heat-affected zone issmaller. With the increasing of welding layer, the number of thermal cycles betweendifferent layers and remelting that the weld experienced is more, thus the tensilestrength of the weld is stronger and the impact resistance is lower, and fracture mode ischanged, from ductile fracture to mixed fracture. With the increase of interlayer coolingtime, the content of beta is more, the thickness of α-β tissue is bigger, the width of theα lath martensite is changed slightly. When the interlayer cooling time is4min, averagetensile strength is least, elongation is lowest, the impact toughness is worst.