【作者】 王鹏；

【导师】 宋刚；

【作者基本信息】 大连理工大学 ， 材料连接技术， 2009， 硕士

【摘要】 本文在传统直流脉冲MIG焊的基础上,通过脉冲后处理电流和负半波电流的添加,分别采用直流脉冲MIG焊和交流脉冲MIG焊两种工艺实现了对镁合金AZ31B板材的良好焊接。焊后利用光学显微镜、扫描电子显微镜、万能拉伸试验机和显微硬度仪等设备对焊接接头的组织与性能进行了检测分析。采用高速摄像机对电弧及熔滴过渡形式作了分析和研究。实验结果表明:1.在传统直流脉冲MIG焊基础上添加脉冲后处理电流,形成了所使用的直流脉冲MIG焊工艺。采用这种焊接工艺,可以实现镁合金的连续焊接,焊缝表面成形美观。其焊缝区晶粒和母材相比不仅得到细化,而且均匀。热影响区的晶粒大小与母材相比有所长大。但是焊接参数范围比较窄,焊接参数之间的匹配也不太容易。熔滴过渡形式,只能可以实现大滴过渡的熔滴过渡形式。其焊接接头平均抗拉强度为母材的96%,平均延伸率也可以达到母材的58%。2.在传统直流脉冲MIG焊基础上不仅添加脉冲后处理电流,而且添加负半波电流,形成了交流脉冲MIG焊工艺。采用交流脉冲MIG焊工艺,焊接过程电弧更加稳定,焊缝表面成形美观。其焊缝区晶粒和母材相比不仅得到细化,而且均匀。热影响区的晶粒大小与母材相比有所长大。采用交流脉冲MIG焊工艺,其焊接参数范围不仅得到扩大,而且焊接参数之间的匹配也更容易。对焊接过程稳定性起最大作用的是脉冲后处理电流和负半波电流。通过这两个参数的调节,可以实现对焊丝的热输入精确控制。采用交流脉冲MIG焊可以实现大滴过渡和射滴过渡两种过渡形式。其焊接接头平均抗拉强度为母材的97%,平均延伸率也可以达到母材的78%,断面收缩率是母材的199%。3.采用交流脉冲MIG焊工艺,对焊缝的变形和残余应力进行了研究。试验结果表明,平行于焊接方向呈现膨胀的趋势。垂直焊接方向呈现收缩的趋势,垂直于焊接方向上的变形量比平行于焊缝上的变形量要大的多。对于平行于焊接方向的残余应力,在焊缝上,引弧端和熄弧端仍然表现为压应力,与母材应力性质相同;焊缝中段表现为拉应力。在热影响区上,仍然表现为压应力。对于垂直于焊接方向的残余应力,引弧端和熄弧端垂直于焊接方向的残余应力全是压应力,焊缝区压应力有所释放。焊缝垂直平分线上,焊缝区具有较大的拉应力,热影响区压应力有所增加。更多还原

【Abstract】 In present study, direct current (DC) pulsed MIG welding and alternating current (AC) pulsed MIG welding are developed by adding a pulse rework current and negative current, based on traditional DC pulsed MIG welding. AZ31B plates are welded with these two processes separately. The microstructure, mechanical property and hardness were investigated by the metal phase microscopy, scanning electron microscope, tensile testing machine and hardness instrument after welding. The detachment of droplets and arc shape is documented with high-speed-camera. The result shows below.1. DC pulsed MIG welding that we used is formed by adding a pulse rework current based on traditional DC pulsed MIG welding. Continuous weld beads can be obtained. The range of parameters is still narrow, and the parameters can not match with each other easily. Globular transfer form can only be realized. The average ultimate tensile strength of weld beads is 96% of base metal and the average elongation is 58% of base metal.2. AC pulsed MIG welding is formed by adding a pulse rework current and a negative current. A stable welding procedure and continuous joints can be obtained. When this process is used, not only the welding procedure is stable under a wide range of welding parameters, but also the parameters can be matched with each other easily. The most important factors for MIG welding are negative electrode (EN) ratio and pulse rework current Two metal transfer forms of globular and pulse transfer can be realized. The average ultimate tensile strength of weld beads is 97% of base metal; the average elongation is 78% of base metal; the average contraction is 199% of base metal.3. The deformation and residual stress of weld bead are studied using AC pulsed MIG welding process. There are several results. The deformation paralleled to weld bead expands. The deformation perpendicular to weld bead shrinks. For the stress paralleled to weld direction on the weld bead, it is compression stress at arc side. It is tension stress at weld bead. For the stress perpendicular to weld direction, it is compression stress at arc side. For the stress on the midnormal line of weld, it is tension stress at weld bead and it is compression stress at HAZ.更多还原