【作者】 梁瑛；

【导师】 胡绳荪；

【作者基本信息】 天津大学 ， 材料加工工程， 2018， 博士

【摘要】 本课题提出“TIG-CMT复合焊接”新方法与新工艺,主要是指TIG电弧在前、CMT电弧在后,双电弧之间有一定距离,与一般电弧复合、通过电弧相互作用来增加电弧能量的方法和机理不同,TIG和CMT电弧没有直接的相互作用,为两个相互独立的电弧,既保证了CMT焊接熔滴过渡的可控性,又可以提高工件的热输入,从而扩大了CMT焊接板厚的适用范围,改善焊缝成形与接头显微组织结构,提高接头性能。通过高速摄像和电信号同步采集系统对铝合金材料直流CMT的稳定短路过渡的临界点进行了确定。在焊机一元化试验条件下,能够保证稳定短路过渡的焊接电流临界点为96 A(对应的送丝速度为5.3 m/min);并对不同参数下的TIGCMT复合焊的电信号,电弧形态和熔滴过渡模式进行了试验,分析了复合焊电弧在交互作用下的形态和熔滴过渡形式的变化规律。发现通过提高CMT电流,拉大CMT焊丝与TIG钨极间的距离和保持两枪垂直的方法可以提高TIG-CMT复合焊的焊接稳定性。利用ABAQUS软件建立了TIG-CMT复合焊的温度场模型,通过编写子程序成功将面热源与体热源同时加载到工件上,提高了计算的准确性。对比了CMT焊、TIG焊和TIG-CMT复合焊这三种焊接方法的温度场和热循环曲线,可知复合焊热循环曲线具有双峰特点,表明了TIG焊和CMT焊对工件的复合热作用,工件加热温度较高,冷却速度较慢。开展了TIG-CMT复合焊6061铝合金对接工艺试验研究。结果表明:TIG电流和焊接速度对焊接接头的宏观形貌影响较大;随着热输入的增大,焊缝的微观组织粗化,热影响区和部分熔化区宽度增加,接头力学性能降低;焊接接头力学试验表明,其主要为延性断裂,断口内分布大量韧窝;接头中存在力学性能薄弱区,而接头中的析出相转变机制,是导致其力学性能下降的主要原因。开展了TIG-CMT复合焊6061铝合金堆焊工艺试验研究。试验表明:通过TIG电弧的加入,起到了对母材的预热效果;TIG-CMT复合焊显著降低了CMT堆焊焊缝的接触角,得到了良好的堆焊成形;与CMT焊缝相比,复合焊焊缝出现了明显的部分熔化区;通过对单道复合焊采用正交试验得到了焊接工艺最优参数,并利用最优参数成功实现了复合焊的多道堆焊,焊缝具有良好的力学性能。更多还原

【Abstract】 The dissertation proposed a new method and new technology: "TIG-CMT" hybrid welding.This method mainly refered to the TIG arc in front and CMT arc in back,a certain distance between the two arcs.Compared with general hybrid arc,the mechanism was different from the method of through arc interaction to increase the arc energy,TIG-CMT hybrid had no direct interaction between two arcs,TIG arc and CMT arc were independent of each other.It was not only to ensure the controllability of the droplet transition of CMT welding,but also improve the thermal input of workpiece,so as to expand the application range of the plate thickness of CMT welding.In this way,the performance and microstructure structure of the joint could be improved.Under the CMT synergic welding process,the critical point for stable short-circuit DC CMT welding in aluminium alloy was determined by high-speed camera and synchronous electrical signal acquisition system,and its critical point was welding current: 96 A(wire feeding speed: 5.3 m/min).Under different parameters of TIG-CMT hybrid welding,the experiment of electrical signals,arc shape and droplet transition were examined.Subsequently,the morphology of hybrid welding arc under the interaction and the changing discipline of droplet transfer mode were analyzed.The result showed that with the increase in CMT current,widening the CMT wiretungsten electrode distance and maintaining two torches vertical to the workpiece could improve the process stability of TIG-CMT hybrid welding.The temperature field model of TIG-CMT hybrid welding was established by using ABAQUS software.Subroutine were programmed to load;both surface heat source and body heat source were successfully loaded onto the workpiece at the same time,which improved the accuracy of calculation.The temperature field and thermal cycle curves of CMT,TIG and TIG-CMT welding methods were compared.The thermal cycle curves of the hybrid welding had both the characteristics of TIG and CMT welding in time sequence.The overall temperature field was higher and the cooling rate was slower.Experimental on butt joining of 6061 aluminum alloy by TIG-CMT hybrid welding process was conducted.With the increase in heat input,the microstructure of the joint grew,the width of the HAZ and PMZ increased,and the mechanical property decreased.There was a weak zone of mechanical property in the joint.The tensile experiment of welding joint showd that it was mainly ductile fracture,and the fracture was composed of dimples.Besides,the precipitated phase transformation mechanism in the joint is the main cause for the decrease of mechanical property.Experimental on cladding of 6061 aluminum alloy by TIG-CMT hybrid welding was also conducted.The experimental results showed that TIG-CMT hybrid welding could significantly reduce the contact angle of CMT cladding and provide better weld shaping.Compared with CMT welding,the cladding by hybrid welding had apparent partially melted zone(PMZ).The optimized parameters of welding process were obtained by orthogonal experiment.The multi-passes clad was successfully obtained by using the optimized parameter,and good mechanical properties were obtained.更多还原