アルミニウムのフラックスレスろう付性に及ぼすろうへのBi添加の効果

抄録

Fluxless brazing was made in vacuum down to 2 × 10^-5 torr at 600°C for 3 mn using Al-10% Si-1%Mg filler alloys containing Bi up to 0.4% in the form of brazing sheet cladding. Fluxless brazing was also made in reduced nitrogen down to 10^-1 torr and in purified nitrogen at 760 torr using Al-10%Si filler alloys containing Bi up to 0.4%. An addition of Bi particularly 0.05 to 0.1% to brazing sheet claddings improves the length of filled clearance and leg length ratio in all the brazing processes. Although the flow factor is unchanged, the fillet form is homogenized by the usie of Bi bearing brazing sheets. Bi freely exists in Al-10%Si filler alloys, while it combines with Mg in Al-10% Si-1%Mg filler alloys. The mechanism of improving the brazability by Bi addition in vacuum brazing processes is attributed to that Mg and Bi or Bi vaporize at low temperatures breaking down the surface oxide film on brazing sheets, and Mg and Bi prevent reoxidation of the fresh surface produced during heating by gettering oxygen in the brazing furnace.