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Occurrence of sub-critical heat affected zone liquid metal embrittlement in joining of advanced high strength steel
Journal of Materials Processing Technology ( IF 6.3 ) Pub Date : 2021-02-01 , DOI: 10.1016/j.jmatprotec.2020.116917
C. DiGiovanni , A. Ghatei Kalashami , F. Goodwin , E. Biro , N.Y. Zhou

Abstract Advanced high strength steels (AHSS) used in automotive structural components are commonly protected using zinc coatings. However, the steel/zinc system creates the potential for liquid metal embrittlement (LME) cracking during welding. In this study, the effect of angular welding electrode misalignment as recommended by industry was investigated and resulted in LME cracking in the sub-critical heat affected zone (SCHAZ) which is a region where LME has not been previously observed. The largest misalignment case of 6° resulted in bending of the work piece and an angled weld nugget/heat affected zone (HAZ), causing LME cracks in the lower temperature HAZ regions. SEM and EBSD analysis characterized the LME crack area as the SCHAZ and below the Ac1 transformation temperature. Furthermore, dilatometry analysis showed the Ac1 temperature to be approximately 660 °C, meaning LME occurred below the traditional 700 °C minimum threshold. In addition to this novel observation of LME before transformation and at low temperature, it was also noted that only misalignment beyond 2° promoted LME cracking. The low angle 2° case was observed to be statistically the same using a Student’s t-test (α = 0.05) on 6 welded samples for LME crack severity compared to a standard 0° case.

中文翻译:

先进高强钢连接中亚临界热影响区液态金属脆化的发生

摘要 用于汽车结构部件的高级高强度钢 (AHSS) 通常使用锌涂层进行保护。然而,钢/锌系统会在焊接过程中产生液态金属脆化 (LME) 开裂的可能性。在这项研究中,研究了行业推荐的角度焊接电极错位的影响,并导致亚临界热影响区 (SCHAZ) 中的 LME 开裂,这是以前未观察到 LME 的区域。最大的 6° 错位情况导致工件弯曲和成角度的焊核/热影响区 (HAZ),导致低温 HAZ 区域出现 LME 裂纹。SEM 和 EBSD 分析将 LME 裂纹区域表征为 SCHAZ 且低于 Ac1 转变温度。此外,膨胀计分析显示 Ac1 温度约为 660 °C,这意味着 LME 低于传统的 700 °C 最低阈值。除了在转变前和低温下对 LME 的这种新颖观察之外,还注意到只有超过 2° 的错位才会促进 LME 开裂。使用Student's t-test (α = 0.05) 对6 个焊接样品进行LME 裂纹严重程度观察,观察到低角度2° 情况与标准0° 情况在统计上相同。
更新日期:2021-02-01
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