New Technology Enables to Braze Al Without Flux

Jul 8, 2014
Motohiko Hamada, journalist

Taiyo Nippon Sanso Corp developed a technology to braze aluminum (Al) without a flux by using a brazing material containing argon (Ar) and magnesium (Mg) in cooperation with Mitsubishi Aluminum Co Ltd.

The company aims to apply the technology to the coolers of the control units of HEVs (hybrid electric vehicles) and electric vehicles (EVs) as well as heat exchangers that use high-strength parts containing Mg and are for automobiles and residential air conditioners.

Al brazing is used for the production of heat exchangers having many junctions such as automotive heat exchangers. Currently, there are two mainstream methods. One is a brazing method that uses a noncorrosive fluoride-based flux in a nitrogen gas atmosphere. The other is a vacuum brazing method that uses a vacuum atmosphere.

The brazing method using a noncorrosive flux is used for many automotive heat exchangers. However, because fluorine (F) in the flux reacts with Mg existing in the Al alloy, causing defective brazing, the method is not suited for Al alloys containing Mg. Therefore, it cannot be used for high-strength Al alloys.

On the other hand, with the vacuum brazing method, Mg contained in the brazing material evaporates when it is melting, removing the remaining oxygen (O2) and moisture in the furnace and reducing the oxide film on the surface of Al. However, in a high-vacuum atmosphere, zinc (Zn) contained in the Al alloy evaporates, too, lowering corrosion resistance.

To solve the problems of the two methods, Taiyo Nippon Sanso engaged in the research on a brazing technology that does not use a flux under ordinary pressure. As a result, it developed a new brazing method that uses an Ar gas atmosphere and a brazing material containing Mg and does not use a flux. It enables to eliminate the process of applying a flux, use an alloy containing Mg and prevent quality determination caused by the evaporation of Zn.

Furthermore, because O2 and nitrogen (N2) in the atmosphere inhibit the wettability of melted wax, Taiyo Nippon Sanso developed a technology to control the densities of O2 and N2 in Ar gas. As a result, it becomes possible to reduce the usage of Ar gas by about 40%.