Mechanism of Void Formation during Brazing of Ni Paste Brazing Filler Metal

Abstract:

Automobiles are equipped with EGR (Exhaust Gas Recirculation) coolers to improve fuel economy and exhaust gas suppression performance. Inside the EGR cooler, the moisture in the gas is condensed by cooling the hot exhaust gas. This condensed water is highly corrosive because sulfur oxides dissolve. Therefore, stainless steel and Ni-based brazing metal having excellent corrosion resistance are used for the EGR cooler.Until now, stainless steel has been brazed under a vacuum atmosphere. However, there are increasing opportunities to braze stainless steel in an inert atmosphere gas at atmosphere for cost reduction and mass production. In this case, a paste-type brazing filler metal consisted of a powder brazing filler metal and a binder is used. As is well known, a debinding process that volatilizes the binder is needed. From previous research in this laboratory, it is clarified that the binder causes voids. In addition, it is said that the size and location of voids generated at the brazed joint affect the product performance. On the other hand, the detailed investigation about the influence which the installation position of a paste type brazing filler metal on the void formation process has not yet been made. Therefore, in this study, the arrangement method and influence on heating rate and debinder temperature on void formation were investigated by X-ray CT.

• Periodical: Materials Science Forum (Volume 1016)
• Pages: 1218-1222
• DOI: https://doi.org/10.4028/www.scientific.net/MSF.1016.1218
• Online since: January 2021
• Authors: Mana Sakai*, Tatsuya Sasaki, Yasuyuki Miyazawa
• Keywords: Brazing, EGR Cooler, Joining, Ni Brazing Filler Metal, Paste Brazing Filler Metal, Stainless Steel, Void, X-Ray Microscopy

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