Vacuum brazing tests on powder aluminum brazing filler metals

Vacuum brazing tests on powder aluminum brazing filler metals were conducted using various atomized Al-Si-Mg powders to investigate their applicability for the vacuum process. The effect of atomizing condition, powder size and filler metal composition has been studied to obtain an optimum powder for the vacuum process. After brazing a part of each filler metal used made no contribution to the fillet formation and coalesced on the base metal. This indicated non-wetting tendencies among filler metal powders. Brazability was evaluated by the percentage of the filler metal remaining as fillet by measuring the weight change before and after brazing. After brazing, voids were found in the formed fillet. Although, completely sound fillets were not obtained, fine powders and air atomized powders gave better brazability than coarse powders and those atomized in argon gas atmosphere. The difference in vaporization characteristics of magnesium in the filler metals seemed to be responsible for void formation and poor brazability of the powder filler metals. Mixing of the filler metals with Al-Mg powder was found to be effective for the improvement of the fillet formation, however, completely sound fillets were not obtained. It is believed that both the control of magnesium vaporization rate and improvement in the quality of the vacuum are important to obtain sound fillets.