【作者】 范玮；

【导师】 闫久春；

【作者基本信息】 哈尔滨工业大学 ， 材料加工工程， 2011， 硕士

【摘要】 在进行紫铜厚板的气体保护电弧焊时,热裂纹成为构件失效的主要原因。通常认为热裂纹的产生是由于在焊接过程中母材的氧化使晶界处偏聚Cu₂O与Cu的低熔共晶,在收缩应力下产生局部应力集中。本文首先从使用ERCu焊丝焊接紫铜厚板的研究出发分析氧元素在热裂纹中起的作用;降低氧含量对裂纹的影响以及氧对金属高温性能的影响。随后通过理论分析和试验研究指出ERCuNi焊丝可有效抑制热裂纹。采用刚性拘束裂纹试验评定不预热GTAW焊接紫铜厚板的裂纹倾向。当ERCu焊丝为填充材料时,宏观裂纹几乎贯穿整条焊缝,在一次结晶的柱状晶晶间有微裂纹。研究表明,在柱状晶晶界处的Cu₂O与Cu的低熔共晶使晶界弱化,在应力的作用下开裂。由此可知ERCu焊丝中的脱氧元素Si、Mn、P的含量不足,无法去除焊缝中的氧。为了考察降低焊缝含氧量对热裂纹的影响,自制了氩气仓,以实现良好的氩气保护,达到排除空气中氧的干扰的目的。并在这样的保护条件下用ERCu焊丝再次进行刚性拘束裂纹试验。焊缝表面无宏观裂纹产生。随后通过ERCu熔敷金属和ERCu焊丝高温性能的比较得出结论氧可以使脆性温度区间变宽。综上所述,对于紫铜厚板的GTAW,焊缝中的含氧量对热裂纹的产生与否起决定作用,因此可通过在焊丝中加足够多的脱氧元素来抑制热裂纹。当用ERCuNi焊丝作为填充材料时,焊缝成形良好,表面裂纹率、断面裂纹率均为零。研究表明,Ni可与Cu₂O发生反应,生成Cu和NiO,在焊缝中起到脱氧的作用,进而抑制了Cu₂O与Cu的低熔共晶的产生,使热裂纹得到控制。同时由于ERCuNi焊丝的熔点高于母材熔点,使得焊缝凝固时最薄弱位置不在受热应力最大的焊缝中心,相当于减小了焊缝薄弱位置受到的应力,从而减小热裂纹倾向。更多还原

【Abstract】 Hot cracking has became a main problem which plays a passive role in usage of copper, when we weld the copper plates with large demension. In general, the oxidation of base metal lead the low melting point of Cu₂O and Cu to get together in the boundary of crystals and stress concentration may occur in the effect of stress. In this paper, from the resarch on the rigid restraint cracking test using ERCu filler matal, we analyse the effect of oxygen on the hot cracking, the cracks in the condition of oxygen reducing greatly and the influence of oxygen on tensility in high temperature. In additon, ERCuNi is proved to suppress the hot cracking after the theoretical analysis and the experiments.In the rigid restraint cracking test where ERCu is used as filler matal, the craking almost lies through all the joint. That’s because the deoxy element Si, Mn is insufficient, so in the boundary of the columnar crystals there is the low melting point of Cu₂O and Cu and the stress lead the boundary to crack.A box for an anaerobic environment has been made and the rigid restraint cracking test in the box to make sure the effects of the tiny oxygen content on the cracking. The cracking has been suppressed well. Then from above all the results we can get conclusion that the oxygen content in the joint plays a crucial role in the existance of the hot cracking and we can use the filler metal which is added enough deoxy element to suppress the cracking for copper.While ERCuNi is used in the rigid restraint cracking test, the joint is formed very well, and there is not a surface cracking and section cracking at all. Form thermodynamics anysis, we know Ni is more active than Cu, and it can deoxidize form the joint, then the low melting point of Cu₂O and Cu can be eliminated so that the cracking got be controlled. On the other hand, due to ERCuNi filler metal’s higher melting point, compared with Cu base metal, the weakest position doesn’t locate at the centre line of joint in the process of the solidification. So it can avoid the great tensile stress, and get little tendency of the hot cracking.更多还原