钢的热源辅助搅拌摩擦焊装备与工艺研究

发布时间：2018-04-05 12:46

本文选题：热源辅助　切入点：搅拌摩擦焊　出处：《南京理工大学》2017年硕士论文

【摘要】：针对钢等高强度、高熔点材料难以直接实现搅拌摩擦焊、搅拌头易磨损等问题,本文设计了薄钢板专用搅拌头和热源辅助搅拌摩擦焊装置,研究了工艺参数对薄板Q235钢和304不锈钢热源辅助搅拌摩擦焊工艺成形、组织、显微硬度、力学性能的影响规律,分析了断口形貌与断裂机制,揭示了强化组织形成与增强机理。通过对Q235和304不锈钢焊缝表面成形评级研究发现,一般情况下,转速和焊接电流增加或焊速降低,表面飞边金属堆积量和匙孔前熔化凝固金属量增加,反之减少。转速过高或过低,匙孔前侧熔化凝固金属量变化不明显,是因为转速过低,FSW产热不足以使TIG电弧区材料升温熔化。转速过高,摩擦系数降低,搅拌头产热趋于稳定值,总热输入趋于稳定。焊接热输入过大时,焊缝背部前进侧附近出现凹槽。对TIG影响区截面宏观形貌的研究结果表明,FSW产热与电阻热和电弧热叠加,电弧影响区熔深增加;搅拌头高速旋转挤压使软化材料填充至对接缝间隙,在高温强流变作用下形成挤压塑变焊接区,转速越高,挤压塑变焊接区厚度越大。通过对Q235钢和304不锈钢焊缝组织研究发现,焊缝横截面微观组织基本分为轴肩搅拌区、热机影响区、热影响区、电阻加热区、母材金属5个区域。表层细晶区为铁素体或奥氏体再结晶细晶层,"根茎状"组织为再结晶铁素体或奥氏体细晶,Q235焊缝存在马氏体"根须状"组织和过渡层。焊缝整体硬度高于母材硬度,Q235钢近表面区硬度最高达252.9HV,304不锈钢厚度中心线最高硬度达360HV。转速和焊接电流越高或焊接速度越低,接头硬度升高。力学性能研究结果表明,对Q235,当转速为800r/min,焊速为40mm/min,电流为60A时,接头抗拉强度最高达514MPa,比母材强度高20%,是因为焊缝中细晶区和马氏体过渡层提供了细晶强化和相变强化。并且转速为800～1200r/min时,转速越高,接头抗拉强度越低;对304不锈钢,正交试验参数对接头抗拉强度的影响顺序为焊接电流焊接速度搅拌头转速;当转速为800r/min,焊接速度为50mm/min,焊接电流为60A时,抗拉强度最大达650MPa,与母材近等强。
[Abstract]:In view of the problems of high strength and high melting point materials such as steel, it is difficult to realize friction stir welding directly, and the friction stir head is easy to wear, this paper designs a special stir head for thin steel plate and a heat source assisted friction stir welding device.The effects of process parameters on the forming, microstructure, microhardness and mechanical properties of FSW for Q235 steel and 304 stainless steel were studied. The fracture morphology and fracture mechanism were analyzed, and the formation and strengthening mechanism of strengthened microstructure were revealed.Through the research on the surface forming rating of stainless steel Q235 and 304 stainless steel, it is found that, in general, the rotating speed and welding current increase or decrease, the amount of surface flash metal and the amount of melting solidified metal before keyhole increase, whereas the amount of solidified metal decreases.If the rotational speed is too high or too low, the amount of molten solidified metal in front of the keyhole does not change obviously, because the low rotational speed of FSW is not enough to heat up and melt the material in the TIG arc region.When the rotational speed is too high, the friction coefficient decreases, the heat production value of the mixing head tends to be stable, and the total heat input tends to be stable.When the welding heat input is too large, the groove appears near the forward side of the back of the weld.The results of the study on the macroscopic morphology of the section of the influence zone of TIG show that the heat production of the affected zone is superimposed with the heat of resistance and arc heat, and the penetration of the zone affected by the arc increases, and the high speed rotating extrusion of the stirring head makes the softened material fill the gap of the butt joint.The extrusion plastic welding zone is formed under the action of high temperature and strong rheology. The higher the rotational speed, the greater the thickness of extrusion plastic deformation welding zone.The microstructure of weld of Q235 steel and 304 stainless steel is studied. The microstructure of cross section of weld is divided into five regions: shaft-shoulder stirring zone, heat affected zone, heat affected zone, resistance heating zone and base metal.The surface fine grain area is ferrite or austenite recrystallized fine crystal layer, the "rhizomorphic" structure is recrystallized ferrite or austenite fine crystal Q235 weld metal, there is martensite "root whisker" structure and transition layer.The overall hardness of the weld is higher than that of the base metal. The highest hardness of the near surface area of Q235 steel is 252.9 HVC304 stainless steel thickness centerline and the highest hardness is 360 HV.The higher the rotating speed and welding current or the lower the welding speed, the higher the joint hardness.The higher the rotational speed is, the lower the tensile strength of the joint is, and for 304 stainless steel, the influence of orthogonal test parameters on the tensile strength of the joint is in the order of welding current welding speed and stirring head speed.When the rotational speed is 800 r / min, the welding speed is 50 mm / min and the welding current is 60 A, the maximum tensile strength is 650 MPA, which is nearly as strong as the base metal.
【学位授予单位】：南京理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG453.9

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