2195铝锂合金焊接热裂纹敏感性和焊接材料研究

【作者】 李小飞；

【导师】 李晓红； 熊华平；

【作者基本信息】 北京航空材料研究院 ， 材料学， 2007， 硕士

【摘要】 2195铝锂合金具有强度高、密度低的特点,是新一代运载火箭和航空结构的备选材料。近年来,国内外对该合金成分和性能进行了大量的研究,但对其焊接性的研究较少。因此本文对2195合金焊接热裂纹敏感性和焊接材料进行了研究。试验中对板厚为2mm的2195合金板材进行了钨极氩弧焊接,选用横向变拘束试验评定焊接热裂纹敏感性,并通过鱼骨形试验研究控制焊接热裂纹的措施。运用传统光学金相技术并结合扫描电镜(SEM)、透射电镜(TEM)分析方法以及焊接热模拟技术对裂纹形貌和接头组织进行观察和分析。与LC9CS和д16qчT等其他铝合金相比,2195合金具有较大的焊接热裂纹敏感性,它的临界应变量εmin<0.19%。2195合金的焊接热裂纹主要分布于焊缝(WM)、焊缝边缘等轴晶区(EQZ)、弧坑等部位,其中焊缝和焊缝边缘等轴晶区对焊接热裂纹最敏感。裂纹均沿晶界或枝晶间产生和扩展,这与这些部位存在共晶液相有关。它的产生机理是:在焊接非平衡凝固过程中,溶质元素在晶界和枝晶间偏析,形成低熔共晶组织,以液膜形式铺展润湿晶界;同时由于共晶液相数量较少不能通过“治愈”效应回填凝固过程中已产生的裂纹,造成2195合金具有较大的焊接热裂纹敏感性。在2195合金焊缝边界存在精细等轴晶区域(EQZ),等轴晶的晶界具有共晶成分,造成EQ2区域也易产生焊接热裂纹。通过填充焊接材料不能消除EQZ。在ER2319焊接材料成分基础上,研制了A1-Cu-Ag-Mg和Al-Cu-Sc两类合金化体系的焊接材料,并与商用ER4043焊接材料作对比。焊接接头性能测试和组织分析结果表明,不同合金化体系焊接材料对应的焊缝力学性能差别明显。含Sc焊接材料焊缝强度较其他焊接材料焊缝强度高,高于330MPa,这是由于Sc对焊态焊缝金属产生了细晶强化作用。Sc元素在焊缝中最佳含量范围为O.14%~0.32wt%:当Sc含量超过0.32wt%)后,将对力学性能产生不利影响。通过本项目的研究,Sc含量在一定范围内的焊接材料具有较低焊接热裂纹倾向和较好的接头综合力学性能,可以用于2195合金的实际焊接生产。商业ER4043焊接材料也具有较好的抗焊接热裂纹性能,在接头力学性能要求不高的情况下,可用于2195合金的焊接。更多还原

【Abstract】 The aluminum-lithium (Al-Li) alloy 2195 is a candidate material for the next generation of launch vehicles and aero-engineering structures because of its low density and high strength. While considerable research efforts have been devoted to composition and properties of the base metal, little attention has been paid to the study of its weldability. The purpose of this thesis was to study the welding hot cracking susceptibility and welding materials of 2195 Al-Li alloy.Domestic 2195 Al-Li alloy plate, 2mm in thickness, was welded by argon tungsten-arc welding (GTAW). By using the transvarestraint test, the welding hot cracking susceptibility of 2195 alloy has been evaluated; and by houldcroft test, the possibility for improving the welding-cracking -resistance has been discussed. The fractography of cracking and microstructure of welded joint were systemically investigated by means of optical microscope, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and welding simulation technology.The results have shown that the critical strain is below 0.19%. As a result, the welding hot cracking susceptibility of 2195 alloy was larger than other aluminum alloys such as LC9CS andд16qчT . The welding hot cracking of 2195 alloy took place among the following locations: weld metal, fusion boundary equiaxed zone and weld pool crater, in which the weld metal and fusion boundary equiaxed zone (EQZ) were the most susceptible to the welding hot cracking. All of the cracks originated and propagated along the grain boundary or boundary between dendrites. This is associated with the eutectic constituent. The mechanism of welding hot cracking susceptibility of 2195 alloy can be described as the follows: during the weld metal solidifying, due to the solute element segregation between grains or dendrites, liquid film formed and wetted the boundaries, but the amount of the eutectic liquid was insufficient to heal those formed cracks. For this reason, 2195 alloy exhibited great weld cracking susceptibility.Microscopic examination of the joint microstructure has revealed that fine equiaxed grains zone (EQZ) existed adjacent to the fusion boundary within the fusion zone. Furthermore, the grain boundaries have an eutectic constituent, resulting in the severe welding hot cracking. The EQZ could not be eliminated by selecting any welding filler.Based on the composition of ER2319,two kinds of welding fillers were developed, that is Al-Cu-Ag-Mg and Al-Cu-Sc. The properties of joints welded by these developed welding fillers were contrasted to those of ER4043 welding material. The results have shown that the effects of different microalloying elements such as Sc or Ag+Mg on the mechanical properties were different. The Sc element could eliminate the dendrites of the as-welded weld metal, and cause grain refinement. As a consequence, the properties of welded joints with Sc as alloying element were found to be:σb > 330MPa. The optimum content of Sc element should be within the range from 0.14wt% to 0.32wt% for the mechanical properties of the joints.Taking account of the welding hot cracking susceptibility and the properties of welded joint, the developed Sc-containing welding material could be selected as filler metal for the welding of 2195 aluminum-lithium alloy. In addition, ER4043 can also be used as welding filler for 2195 alloy ,if the requirement for the joint properties is not very high.更多还原