AZ31镁合金MIG焊熔滴过渡行为研究

发布时间：2018-07-04 13:11

本文选题：AZ31镁合金 + 直流MIG焊　；参考：《中北大学》2017年硕士论文

【摘要】：AZ31镁合金由于具备良好的综合性能,现已广泛应用于各行各业,正成为结构镁合金材料领域的研究热点。镁合金结构件在使用过程中,必不可少需要对镁合金进行补焊或连接,因而探究镁合金焊接具有重要的现实意义。目前镁合金焊接并不成熟,镁合金焊接依然面临着诸多问题,镁合金的焊接问题兹待人们进一步解决。本论文基于MIG焊接方法,研究焊接工艺对AZ31镁合金焊接过程的影响,试验中通过改变工艺参数(焊接电流、干伸长度、保护气流量),添加不同的活性剂(KCl、Zn Cl2、Ca Cl2、Cd Cl2、Mg Cl2)进行多组实验,采集焊接过程中电弧及熔滴过渡的图片,获得不同工艺下焊后的焊缝接头,对实验结果进行观察、测量、计算、并研究分析相关机理,本文可得出以下结论:(1)焊接电流对电弧及熔滴影响显著,采集的图片显示电流从小到大的过程中,熔滴依次经历了滴状过渡、喷射过渡、射流过渡,其中滴状过渡的可调参数范围广,临界电流值在220A左右,此时电弧稳定,熔滴尺寸与焊丝直径相近。电流从125A逐渐增大的过程中,电弧形态发生了显著的变化,弧长由长变短,弧宽逐渐增大,熔滴过渡尺寸也发生了变化,熔滴尺寸由大变小,过渡频率加快。电流通过影响电弧及熔滴过渡作用到焊缝成形上,熔宽增宽,熔深加深,余高增高。(2)实验结果表明干伸长度会影响熔滴过渡中的临界电流,干伸长度增加,临界电流变大。在其他条件一定的情况下,干伸长度增大,焊丝的电阻值增加,电压增大,熔滴尺寸变大,弧长变长。对焊缝的研究发现干伸长度过小,会造成焊缝过高,成形不良。干伸过大,电弧不稳,产生大量飞溅,焊缝成形性差。(3)在一定的范围内,保护气流量增大,电弧会发生收缩,电弧越来越稳定,熔滴尺寸有所减小。气流量过小,会卷入空气,电弧紊乱,造成飞溅,且保护效果不良,造成焊缝氧化;气流量过大,电弧吹力加剧,易造成飞溅。(4)添加不同的活性剂对电弧及熔滴过渡会产生不同的影响,Ca Cl2活性剂使得弧宽增大,熔滴尺寸明显增大,熔滴过渡周期延长,阻碍了熔滴的过渡,熔深变浅,余高稍有减小。Cd Cl2活性剂和Zn Cl2活性剂收缩了电弧,使熔滴尺寸变小,焊缝的余高和熔宽大大减小。添加KCl活性剂后,电弧扩展很大,变为伞状,电弧宽度变宽,熔滴尺寸变小,沿竖直轴向方向过渡,过渡周期减小,过渡平稳,由滴状过渡转变为喷射过渡,KCl活性剂促进了熔滴过渡,余高熔深均增大,熔宽的增加幅度很大。Mg Cl2活性剂对熔滴过渡影响不大,电弧稍有收缩,焊缝熔深加深,但加深幅度不大。
[Abstract]:AZ31 magnesium alloy has been widely used in various industries due to its good comprehensive properties, and is becoming a research hotspot in the field of structural magnesium alloy materials. In the process of using magnesium alloy structure, it is necessary to weld or connect magnesium alloy, so it is of great practical significance to explore the welding of magnesium alloy. At present, magnesium alloy welding is not mature, magnesium alloy welding is still facing many problems, magnesium alloy welding problems need to be further solved. Based on the MIG welding method, the effect of welding process on the welding process of AZ31 magnesium alloy is studied in this paper. Different kinds of active agents (KCl-Zn Cl2Ca-CaCl2Cd-Cl2Mg-Cl2) were added to the experiments. The images of arc and droplet transfer during welding were collected, and the weld joints after welding under different processes were obtained. The experimental results were observed, measured and calculated. The results are as follows: (1) the welding current has a significant effect on the arc and droplet. The collected pictures show that the droplet has experienced droplet transition, jet transition and jet transition. The adjustable parameters of the droplet transition are wide, the critical current is about 220A, the arc is stable and the droplet size is close to the wire diameter. In the process of increasing the current from 125A to 125A, the arc shape changed significantly, the arc length became shorter, the arc width gradually increased, the size of droplet transfer changed, the size of droplet changed from large to small, and the transition frequency was accelerated. Through the influence of arc and droplet transfer on the weld formation, the weld width widens, the penetration deepens, and the residual height increases. (2) the experimental results show that the dry elongation will affect the critical current in the droplet transfer, the dry elongation will increase, and the critical current will become larger. Under certain other conditions, the dry elongation increases, the wire resistance increases, the voltage increases, the droplet size becomes larger, and the arc length becomes longer. It is found that the weld is too high and badly formed if the dry elongation is too small. When the dry extension is too large, the arc is unstable, a large amount of spatter is produced, and the welding seam formability is poor. (3) in a certain range, the flux of protective gas increases, the arc shrinks, the arc becomes more and more stable, and the droplet size decreases. If the gas flow rate is too small, it will be involved in the air and the arc will be disordered, causing spatter, and the protective effect is not good, resulting in the oxidation of the weld; if the gas flow rate is too large, the arc blowing force will be aggravated. It is easy to cause spatter. (4) addition of different active agents to the arc and droplet transfer will have different effects on arc width, droplet size and droplet transfer cycle. The residual height decreases slightly. CD Cl 2 active agent and Zn Cl 2 active agent shrink the arc, which makes the droplet size smaller, and the residual height and weld width greatly decrease. With the addition of KCl active agent, the arc expands greatly, becomes umbrella-like, widens the arc width, decreases the droplet size, and transitions along the vertical axis. The transition period is reduced and the transition is stable. The transition from dripping to jet transfer promoted the transfer of droplet, and the remaining high penetration increased. The increase of melting width was very large. The flux of MgCl _ 2 had little effect on the transfer of droplet, the arc contracted slightly, and the weld penetration deepened. But the depth is small.
【学位授予单位】：中北大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG444.74

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