【作者】 赵旭；

【导师】 刘黎明；

【作者基本信息】 大连理工大学 ， 材料加工工程， 2007， 硕士

【摘要】 镁及镁合金材料是目前可应用的最轻的结构材料，被广泛应用于航空、航天、汽车、计算机、通讯和家电等行业。钢是目前应用最广泛的材料之一。这就必然要面临到这两种不同合金的连接问题，焊接是工程材料连接的一种主要方法，因此将镁合金材料与钢进行焊接在工程应用方面有着重大的意义，可以充分发挥镁合金和钢的性能优势，收到“物尽其用”的效果，但目前关于镁合金材料与钢的连接的相关研究方面的报道较少，至今还没有关于两种金属熔焊的报道。本课题采用钨极氩弧焊(TIG)对AZ31B镁合金和304钢异种材料进行焊接，由于镁的熔点低，大约为650℃，沸点为1100℃，而钢的熔点为1539℃。物理性质的巨大差异使得两种金属很难进行焊接进而得到满意的焊接接头。在试验中，我们采取了搭接焊的方式，镁合金在焊接过程中熔化而钢板不熔化，液态的镁润湿固态的钢基体形成了异种金属镁合金和钢的焊接接头。镁基体在焊接的过程中产生烧损、氧化等现象，流失严重不能得到满意的焊缝成型。镁和钢极难互溶，镁钢基体的界面处镁原子和铁原子没有相互扩散形成紧密的结合，同时金属氧化物的大量产生使得焊接接头的性能较低，大约为60MPa。采用激光—氩弧复合热源焊接异种金属AZ31B镁合金和304钢，得到较好的焊缝成型，其焊缝成型为典型的“钉子”形貌，接头性能为90MPa以上。熔深的大小是影响焊接接头性能的重要因素之一，焊接速度、激光离焦量、激光斑点与电弧中心距离等焊接参数的变化会引起焊缝熔深的较大变化。通过电子探针(EPMA)和扫描电镜(SEM)对界面分析发现，采用不同的焊接参数得到镁合金和钢异种金属界面有所不同：在焊接过程中，当选择的参数无法使接头处熔化的镁合金产生蒸发现象，激光能量密度较小时，在界面处镁和钢之间没有明显的相互扩散区域，两种合金在其界面各自凝固；当选择的参数使接头处熔化的镁合金产生蒸发现象，激光能量密度较大时，在界面处镁和钢之间存在明显的扩散区域，镁原子向钢基体中扩散，在扩散区域是镁的氧化物和铁的氧化物组成的混合相。拉伸试验时，断裂总是发生在镁合金和钢的界面上，X射线衍射结果表明拉伸断裂面上存在着大量的金属氧化物。镁钢界面上的氧化物是影响接头性能的关键因素。更多还原

【Abstract】 The joining of dissimilar magnesium alloys to steel is of great industrial significance as it allows design engineers to take advantages of the excellent property sets of both materials. To date, rare reports have been published on joining the two dissimilar metals. Moreover, no reports have been published on the fusion welding of the two dissimilar metals.The dissimilar materials are difficult to weld on their wide difference in physical and mechanical properties. The melting point of magnesium alloy is 650°C and the melting point of steel is 1539°C, so it is difficult for the two metals to melt at the same time and to form a joint. In this paper, dissimilar magnesium alloy and copper were lap welded by TIG welding. During the welding, the magnesium alloy melt but the steel do not, the liquid Mg wetting the solid steel and form the weld joint. The good weld appearance is not obtained because the Mg alloy is heavily oxidized during the process. Magnesium and steel do not mix in the liquid state, Mg atom and Fe atom do not join together with interatomic force at the interface of Mg-Fe and many metallic oxides produced. The shear strength is about 60 MPa.Dissimilar magnesium alloy and copper were lap welded by Laser-TIG hybrid welding, the over-lapped weld joint between Mg alloy and steel could be obtained. Good welding shape was formed, and the weld penetration which determines the mechanical properties of the welded joints is mainly influenced by the laser power. The shear strength is about 90 MPa. The depth of the weld penetration is mainly influenced by the welding parameters. The interface of Mg-Fe is different at the dissimilar welding parameters which are observed by the SEM and EPMA. Mg element diffused into the Fe matrix by form of oxides and reaction, and the two atoms join together with interatomic force when the laser energy density is large; Mg alloy and steel recrystallized separately at the interface of Mg-Fe when the laser energy density is small. The weld fractured at the interfacial region between iron plate and magnesium alloy. Metallic oxides were observed in the interfacial region between iron plate and magnesium alloy. It was the main reason influenced the strength of weld.更多还原