中空構造体の真空ろう付性に及ぼす内外部でのろうの溶融•流動開始時間差の影響

抄録

The object of this study is to improve poor fillet formation at the inside of vacuum brazed-joints in aluminum hollow structures such as drawn-cup type of heat-exchangers. No desirable fillets were formed at the inside of brazed-joints of test specimens which were brazed with an alloy A4004 (Al-10Si-1.2Mg). This fact has so far been ascribed to the surface oxide film. However, we noticed the existence of a certain time-lag in melt and flow of the filler metals between the inside and outside in heating sequence. At the inside the filler metals began to melt and flow above 560°C in the braze heat-cycle as Al-Si-Mg ternary eutectic, and then this molten metal effused to the outside and formed the outside fillets. On the other hand, the outside filler metals did not flow until about 577°C (Al-Si eutectic temperature). Such metal flow mechanism caused the poor fillet formation at the inside. In the test specimen using Al-10Si filler metals for one of the components in order to reduce this time-lag, large fillets were obtained both at inside and outside. In addition, amounts of magnesium vaporing from this test specimen decreased remarkably. Thus the combination of Al-Si-Mg and Al-Si alloys for component filler metals of hollow structures is expected to bring great rationalization in this vacuum brazing process.