Brazing manufacturing technology of plate-fin heat exchanger for solid oxide fuel cells

• Published in: International journal of hydrogen energy 2023-02, Vol.48 (11), p.4456-4468
• Main Authors: Wan, Yu, Jiang, Wenchun, Dong, Zhilong, Xiao, Chengran, Xie, Xuefang, Song, Ming, Zhang, Yucai
• Format: Article
• Language: English
• Subjects: Brazing; Mechanical performance; Microstructure; Plate-fin heat exchanger; Post bonding heat treatment; Solid oxide fuel cell
• ISSN: 0360-3199; 1879-3487
• DOI: 10.1016/j.ijhydene.2022.10.272

The plate-fin heat exchanger (PFHE) is the core equipment used to achieve the high efficiency of solid oxide fuel cell (SOFC), however, the issues of high-performance brazed joints in the manufacturing of the PFHE have been a challenge due to the poor mechanical properties. This study proposes a brazing manufacturing technology of isothermal solidification with the optimized post bonding heat treatment strategy, to synergistically improve the strength-ductility property and homogenize microstructure of brazed joints, aiming at guaranteeing the high energy efficiency of SOFC. The results show that brazing at 1065 °C for 25 min achieves the complete isothermal solidification and an intermetallic-free joint centerline with numerous borides generating in the diffusion-affected zone. Solution treatment then dissolves large quantities of acicular and blocky borides. The uniformity of grain size and kernel average misorientation distribution is also improved due to recrystallization, which becomes more pronounced after solution aging treatment. In addition, solution aging treatment results in an improvement in the ultimate tensile strength of the brazed joint, which is more prominent than that after solution treatment. However, the increase in elongation after solution aging treatment is smaller than after solution treatment, while still much higher than the as-brazed joint due to the dissolution of boride precipitates and growth of twin boundaries. The results demonstrate that the proposed brazing manufacturing technology not only homogenizes microstructure, but also significantly improves strength and ductility, further promoting the long-life operation of SOFC. •A proper brazing technology to fabricate plate-fin heat exchanger of SOFC is proposed.•An appropriate heat treatment strategy to enhance strength and ductility is proposed.•Solution aging gets superior strength but inferior ductility to solution treatment.•Borides dissolution, solid solution and precipitation strengthening enhance strength.•More uniform microstructure, increased recrystallization and twins raise ductility.