Studies Of Sandwich Plates Laser Weldingand Joint Performance With High Strength Steel

Laser welded thin wall lightweight sandwich plate was made by laser welding up anddown plates and core boards, one of the key technology of manufacturing Marine sandwichplate is welding T-joint and lap joint.In order to prove the feasibility of manufacturing welded metal sandwich plates,combining with domestic and foreign studies of laser welding sandwich structure, based onfiber laser welding high strength steel sandwich board as the main research object, themicrostructure and mechanical properties of laser welded joint were system studied byorthogonal test method, nondestructive testing, hardness testing, mechanical performancetest, optical and scanning electron microscope and other methods, studying laser power,welding speed and coke deposition impacting on the weld and the quality of the joint(porosity, slag inclusion and crack, etc); Weld deposited metal and the microstructure ofheat affected zone, distribution characteristics, Vickers microhardness and pulled offperformance was analyzed, the process of T-joint pulled off test, fracture apperance andfracture mechanism were analyzed too; Tensile shear strength, shear fracture morphologyand fracture mechanism of laser lap welding joints, and lap weld width or the constraintwidth which impact on the sample after tensile fracture position, were studied in this paper.Laser welding tests of high strength steel sandwich plates used in ships and warshipsshow that, it have access to welded joint of good forming and suitable cross sectionfeatures size, under appropriate laser welding parameters. High strength steel sandwich structure was welding well and efficient, at the same time, joint structure and mechanicalproperties meet the requirements. Weld width and depth increased when laser powerincreased, weld width and depth decreased when welding speed increased, weld width anddepth decreased when the amount of negative from coke get greater.Microstructure analysis show that, base metal organization are pearlite and ferrite; Weldforming columnar crystal in the process of crystallization, microstructures of weld seamsare lathy martensites; microstructures of heat affected zone coarse grained region mostlyare Lath martensite, and residual austenite, microstructures of heat affected zone finegrained region mostly are Fine pony austenite, residual austenite and a small amount ofcarbide precipitation, and width of heat affected zone is about1mm.Microhardness test of T-joint show that, base metal hardness is about200~230HV0.2, thehardness of heat-affected zone is about230~330HV0.2, the hardness of weld metal is about330~360HV0.2; Grain size of heat-affected zone and weld metal change larger as laser powerincreased, and the hardness decreased; Grain size of heat-affected zone and weld metalchange smaller as welding speed increased, and the hardness increased.T-joint pulled off test show that, T-joint fracture was composite fracture, from both sidesgradually extend to the center; Mechanical performance of T-joint mainly depends on theweld width of faying surface, under the conditions of this test process, it must be at least3times single laser welding, to ensure that the web and panel joint strength is bigger than thestrength of the base metal.The results of tensile shear test of laser welded lap joint show that weld width is the keyfactor which decided location of joint tensile fracture for a certain width and thickness ofsteel plate lap joint. With the increase of weld width, from the weld shear fracture, changeto flexion part fracture, and base metal fracture.