A Study on Penetration of Molten Silver Brazing Filler Metal into Capillary Space and Formation of Void in it by X-ray Fluoroscopy

Abstract

The behavior of molten silver brazing filler metal which is rising a vertical capillary space has been investigated by X-ray fluoroscopy. The specimen used in this experiment, is made of a pair of metal plates and a clearance of capillary space is set from 0.05mm to 0.5mm by metal spacer. After heated to a certain temperature in furnace, the molten metal begins to penetrate into capillary space from lower side of specimen which contacts with it. The movement of the molten metal is observed with 16mm cine camera using X-ray image intensifyer. The penetration rate of molten metal and ratio of void in it are examined from these films. The following results are obtained.
(1) The penetration rates, of molten metals for the specimens of copper are faster than those for mild steel and stainless steel.
(2) With increasing a clearance of capillary space, the initial penetration rate increases but equilibrium penetration height becomes lower, as shownin Fig.6 and 7.
(3) In the experiment, varied the kind of silver brazing filler metal, all kinds of molten metals show good penetration for the specimen of copper, while for the specimen of stainless steel two kinds of molten metals, BAg-7 and BAg-1, exhibit well penetration but a molten metal, BAg-3, is unsatisfactry.
(4) The voids included in capillary space of copper specimen are easy to move, but in the case of mild steel and stainless steel, the voids are hard to move. In general, void tends to increase in the following case of lower heating temperature, narrower clearance and specimen interface roughly scratched by belt sander etc.
(5) In the experiment using the fluxes of KF-H₃BO₃-Na₂B4O₇ systems, with decreasing the viscosity of fluxes, the voids become to decrease considerably.