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Brazing for Magnesium Alloys

Brazing for Magnesium Alloys - Many magnesium alloys can be brazed using techniques similar to those used on other metal except for the temperatures, filler metal and fluxes used. Magnesium thorium alloys developed for high temperature uses, largely in aerospace applications, cannot be brazed. All parts to be brazed are thoroughly cleaned off oil, dirt, grease, coatings, etc., and are made free from burrs. The filler rod for brazing is a magnesium base alloy so that the characteristics of the brazed joint are similar to those of a welded joint. Torch, Furnace or Dip brazing methods are commonly employed for brazing various magnesium alloys. Given below are the flux constituents:
1. For Torch brazing- Potassium chloride, lithium chloride, etc. 2. For Torch, Dip and Furnace brazing Potassium chloride, sodium chloride, lithium/chloride, etc. Torch Brazing Flux paste is made in alcohol. Brazing filler metal is placed on the joint and fluxed before heating or it may be fed as usual. Torch brazing is carried out with a neutral flame. Heat is applied to the job until the flux melts and is continued until the filler metal melts and wets the surface of parent metal. Furance Brazing Components that are to be brazed together are assembled with the filler metal prep laced in or around the joints. In this case, the joints are designed with slotted or recessed grooves to allow for placement of the ring or band of filler metal.
	Joint clearances of 0.10 mm to 0.25 mm should be used for maximum capillary attraction of the brazing filler metal. The joint clearances can be maintained by: (i) Using a brazing jig, (ii) Tack welding, (iii) Staking, (iv) Using self-locking joints. Better results are obtained if instead of flux pastes, dry powder flux is sprinkled along the joint. An electric or gas heated furnace with automatic temperature controls to hold furnace temperature within ± 5°F should be used for furnace brazing. Dip Brazing Filler metal is prep laced in or around the joints. Joint clearance is of the order of 0.10 to 0.25 mm. The parts to be brazed are held in a stainless steel fixture, are preheated in a furnace to 454 to 483°C and then immersed into a molten brazing flux bath.

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