Effect of Bismuth Addition to Brazing Sheet Claddings on Fluxless Brazability of Aluminum(Welding Physics, Process & Instrument)

概要

論文の詳細を見る
Fluxless brazing was made in a vacuum down to 2×10^<-5> torr at 600℃ for 3min using Al-10%Si-1%Mg filler alloys containing Bi up to 0.4% in the form of brazing sheet claddings. Fluxless brazing was also made in reduced nitrogen gas atmosphere down to 10^<-1> torr and in purified nitrogen gas 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 use 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.
大阪大学の論文