INFLUENCE OF OXYGEN-CONTENT ON BRAZEABILITY OF A POWDER ALUMINUM BRAZE FILLER METAL

Brazeability of atomized Al-10Si powder filler metal was investigated in relation to the processing atmosphere and powder size by evaluating the fillet formability on a T-type joint. Atomized powders were mixed with KAlF4-K3AlF6 system noncorrosive brazing flux and organic binder to obtain a brazing paste. The fillet formability depended on the flu x content, atomizing atmosphere and powder size. The paste made of air -atomized powder required more flux to achieve a sound filler formatio n. On the other hand, the argon-atomized powders formed a sound full l ength fillet using the paste with less flux. Both the powders sorted t o remove fine particles and the powders with low-oxygen content were f ound to be suitable for brazing filler metal powders, because they req uired less flux content to obtain sound fillet formation under tile sa me brazing conditions. Atomizing under protective atmosphere and remov ing fine particles were important to obtain excellent brazeability wit h low flux content. The oxygen content of the powder filler metal was found to be a good way to predict brazeability. The less oxygen conten t powder provided excellent brazeability. Removal of the line particle s with less than 30-mu m diameter is the key to obtaining excellent al uminum powder brazing filler metal, because the smaller particles have higher oxygen concentrations.