Filler-Deficient Zone in Arc Welds

不同的填充金属是指填充金属的组成与工件的组成不同。它们通常用于电弧焊，以防止开裂并获得理想的焊接性能。填充金属液滴通过大体积焊接熔池中的强对流与熔化的基底金属混合，并且除了在基底金属附近的区域中焊接金属成分不同于填充金属的区域之外，所得到的焊缝在成分上是均匀的。这种填料不足区（FDZ）的形成归因于弱的焊接熔池对流，因此池边界附近的混合不良。需要对不同的填充金属如何影响焊接熔池凝固过程以及为什么熔化的基底金属可以快速凝固而不与周围的大块焊接熔池混合有基本的了解。本研究的目的是更好地了解电弧焊接FDZ的形成。这些任务包括：（1）通过首先用母材金属（TLB）和焊缝金属（TLW）的液相线温度清楚地限定熔池边界来提出FDZ形成的机制;（2）用可以使TLW与TLB显著不同的所选异种填充金属焊接;（3）检查整个所得FDZ的微观结构和成分分布;（4）计算TLB和TLW以帮助解释所观察到的FDZ形成;以及（5）研究焊接参数对FDZ形成的影响，例如热输入、焊接速度和保护气体。铝和镍铜合金焊接在调查的初始阶段。选择铝合金是因为考虑到不存在固态转变，凝固微观结构比钢或不锈钢更容易理解，并且可靠的数据库和计算机软件可用于计算铝合金中的TLB和TLW。选择Ni-Cu合金是因为简单的类质同晶Ni-Cu相图为TLB和TLW的变化提供了宽范围。该研究的智力价值包括推进对异种填充金属焊接的基本理解，并为更好地理解钢和不锈钢中FDZ的形成提供基础，这对氢裂纹和应力腐蚀开裂敏感。该研究的更广泛影响包括通过更好地理解FDZ的形成来改善焊缝均匀性。鉴于汽车中铝的使用越来越多，以减轻重量和空气污染，这一点非常重要。教育内容包括焊接科学研究生的培训以及固化计算机软件和数据库的相关使用。有用的材料提供焊接冶金教学，涉及焊接本科生，并演示焊接过程中的K-12学生和他们的家长。

Dissimilar filler metals refer to filler metals that differ in composition from that of the workpiece. They are routinely used in arc welding to prevent cracking and to obtain desirable weld properties. The filler-metal droplets mix with the melted base metal by strong convection in the bulk weld pool and the resultant weld is uniform in composition except in the region near the base metal where the weld metal composition differs from that of the filler metal. The formation of this filler-deficient zone (FDZ) has been attributed to weak weld-pool convection and hence poor mixing near the pool boundary. Fundamental understanding is needed on how dissimilar filler metals affect the weld-pool solidification process and why the melted base metal can solidify quickly without mixing with the surrounding bulk weld pool. The objective of this research is to better understand the FDZ formation in arc welds. The tasks include: (1) proposing a mechanism for the FDZ formation by first clearly defining the pool boundary with the liquidus temperatures of the base metal (TLB) and the weld metal (TLW); (2) welding with selected dissimilar filler metals that can make TLW significantly different from TLB; (3) examining the microstructure and composition profiles across the resultant FDZ; (4) calculating TLB and TLW to help explain the FDZ formation observed; and (5) investigating the effect of the welding parameters on the FDZ formation, such as the heat input, the welding speed, and the shielding gas. Aluminum and Ni-Cu alloys are welded in the initial stage of the investigation. Aluminum alloys are selected because in view of the absence of solid-state transformations the solidification microstructure is much easier to understand than in steels or stainless steels and reliable database and computer software are available for calculating TLB and TLW in aluminum alloys. Ni-Cu alloys are selected because the simple isomorphous Ni-Cu phase diagram offers a wide range for varying in TLB and TLW. The intellectual merit of the study includes advancing the fundamental understanding of welding with dissimilar filler metals and providing a basis for better understanding of the FDZ formation in steels and stainless steels, which are susceptible to hydrogen cracking and stress corrosion cracking.The broader impact of the study includes improving weld homogeneity through a better understanding of FDZ formation. This is significant in view of the increasing use of aluminum in automobiles to reduce weight and air pollution. The educational components include the training of graduate students in welding science and the related use of solidification computer software and databases. Useful materials are provided for teaching welding metallurgy, involving undergraduate students in welding, and demonstrating the welding process to K-12 students and their parents.