压铸镁合金TIG焊缝气孔防治措施的研究

发布时间：2018-01-10 12:01

本文关键词：压铸镁合金TIG焊缝气孔防治措施的研究　出处：《重庆大学》2015年硕士论文　论文类型：学位论文

【摘要】：由于压铸母材自身含气量高的原因,在熔焊过程中,压铸镁合金会出现严重的气孔问题。因此,在实际工程应用当中,压铸镁合金通常被认为是不适合熔焊的,这使镁合金压铸件的焊接以及表面缺陷修复技术的发展受到了一定的限制。针对上述问题,本文以压铸镁合金AM60B为对象,采用改变焊接电流频率(50Hz,100 Hz,150 Hz,200 Hz,250Hz)和焊前热处理(温度为150oC,200oC,250oC,300oC)的方法,开展TIG焊焊缝气孔防治的实验研究;实验结果(焊缝气孔的形貌、分布特征以及尺寸等)的检测和表征分别使用了扫描电子显微镜(SEM)、MATLAB软件、X射线衍射仪(XRD)、粒径分析软件Nano measurer 1.2等手段。主要研究结果如下:①焊接电流的频率对焊缝气孔有明显影响:随着交流频率的增加,开口于焊缝表面的孔洞缺陷的数量和尺寸增加,焊缝表面成型有变差的趋势。在纵截面的中部分布着数量较多的大尺寸气孔,在大尺寸气孔根部可观察到小尺寸气孔分布;横截面中气孔主要分布在熔合线附近和焊缝熔融区,少量的气孔分布在焊缝近表面。而且随着交流频率的增加,焊缝气孔率先减少、后增加。②焊接电流的频率对焊缝气孔影响的机理应该是:随着交流频率一定范围内增加,一方面,振动增加,气泡在上浮过程中将与邻近的气泡发生碰撞而合并的几率增加,导致气泡的半径增加,气泡逸出速度增加,气孔率降低;另一方面,促进了熔池液态金属的规律性流动,有利于熔池液态金属温度的均匀性,熔池各个部分的温度梯度降低,熔池的凝固时间延长,有利于气泡的逸出,起到降低气孔率的作用;当交流频率高于一定值的时候,其对熔池的振动作用过于剧烈以及电弧发生不稳定,产生气体卷入现象,焊缝气孔率开始回升。③母材焊前热处理对焊缝气孔有明显影响:与未经焊前热处理母材的焊缝相比,经焊前热处理母材的焊缝表面成型均有不同程度改善,焊缝余高也有所减小,但随着焊前热处理的温度升高,焊缝余高有增加趋势;纵截面上,大尺寸的气孔主要分布在纵截面的中部,小尺寸气孔主要分布在大尺寸气孔根部;横截面上,气孔主要分布在熔合线附近和熔融区,与未经焊前热处理母材的焊缝相比,经焊前热处理母材的焊缝中气孔尺寸和数量均有所减少,但随着焊前热处理温度的升高,气孔大小和数量有增加的趋势。④母材焊前热处理对焊缝气孔影响的机理应该是:随焊前热处理温度升高,一方面有利于母材近表面气体扩散逸出,降低焊缝气孔率;另一方面,母材内部气体扩散均匀化、压强降低,焊接重熔时形成气泡直径减小,不利于气泡浮出,增加气孔率。在热处理温度较低时前者占优;热处理温度较高时后者占优。⑤焊接电流频率和母材焊前热处理对AM60B压铸镁合金TIG焊缝组织无明显影响。
[Abstract]:Due to the high gas content of the die casting base metal, the die casting magnesium alloy will have serious porosity in the welding process. Therefore, in the practical engineering application, the die casting magnesium alloy is usually considered not suitable for melting welding. This makes the development of magnesium alloy die casting welding and surface defect repair technology limited. In view of the above problems, this paper takes die casting magnesium alloy AM60B as the object. The welding current frequency of 50Hz / 100Hz / 100Hz / 100Hz / 100Hz / 100Hz / 100Hz and pre-welding heat treatment (150oC / 200oC) and pre-welding heat treatment (150oC / 200oC) were adopted. The method of 250oC (300oC) was used to study the prevention and cure of TIG welding weld blowhole. The experimental results (morphology, distribution and size of weld porosity) were characterized by scanning electron microscope (SEM), MATLAB software and X-ray diffractometer (XRD). The main results are as follows: the frequency of welding current at 1: 1 has a significant effect on the weld porosity: with the increase of AC frequency. The number and size of holes opening on the surface of the weld increased, and the formation of the weld surface became worse. A large number of pores were distributed in the middle of the longitudinal section. The distribution of small stomata can be observed in the root of large stomata. In the cross section, the porosity is mainly located near the fusion line and the melting zone of the weld, and a small number of pores are distributed near the surface of the weld, and with the increase of AC frequency, the porosity of the weld decreases first. The mechanism of the effect of welding current frequency on weld porosity should be as follows: with the increase of AC frequency in a certain range, on the one hand, the vibration increases. The probability of the bubble colliding with the adjacent bubble increases during the floating process, which leads to the increase of the bubble radius, the increase of the bubble escape velocity and the decrease of the porosity. On the other hand, it promotes the regular flow of molten metal in the molten pool, which is conducive to the uniformity of the temperature of liquid metal in the molten pool. The temperature gradient of each part of the molten pool is reduced, and the solidification time of the molten pool is prolonged, which is conducive to the escape of the bubble. Play the role of reducing porosity; When the AC frequency is higher than a certain value, the vibration effect on the molten pool is too intense and the arc is unstable, resulting in the phenomenon of gas entrainment. The porosity of weld began to rise. 3. Pre-welding heat treatment of base metal had obvious effect on weld porosity. Compared with the weld of base metal without pre-welding, the weld surface of the base metal was improved to some extent. The residual height of the weld also decreased, but with the increase of the temperature of pre-weld heat treatment, the residual height of the weld increased. In the longitudinal section, the large size pores are mainly distributed in the middle of the longitudinal section, and the small ones are mainly distributed in the large stomatal roots. On the cross section, the porosity is mainly located near the fusion line and in the melting zone. Compared with the weld metal without pre-welding heat treatment, the size and number of gas holes in the weld of pre-weld heat treatment base metal are reduced. However, with the increase of pre-welding temperature, the effect of pre-weld heat treatment of base metal on weld porosity should be as follows: with the increase of pre-welding temperature. On the one hand, it is advantageous to the gas diffusion of the near surface of the base metal and the reduction of the porosity of the weld. On the other hand, the gas diffusion in the base metal is homogenized, the pressure decreases, and the diameter of the bubble decreases during welding remelting, which is not conducive to the bubble floating and increases the porosity. The former dominates when the heat treatment temperature is low. When the heat treatment temperature is higher, the frequency of welding current and the pre-welding heat treatment of base metal have no obvious effect on the microstructure of TIG weld of AM60B die-cast magnesium alloy.
【学位授予单位】：重庆大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG444.74

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