GE B50TF204

Fast heating should be employed to avoid liquation (melting and flow of only part of the brazing alloy). AMS 4777 will flow into long, narrow joints, particularly at the higher brazing temperature, in reducing atmospheres (- 60F dew point or lower) or inert atmospheres (-80F dew point or lower). In atmosphere brazing, base metals containing more than 0.5% aluminum and/or titanium are often nickel-plated (0.0005 in. to 0.0015 in. thick depending upon brazing temperature and cycle), if difficulties in wetting and bonding are encountered. On thinner sections or less ductile base metals, brazing should be done at the low end of the brazing range with small clearances, fast heating/cooling cycles, and a minimum quantity of brazing alloy. Recommended joint clearance at brazing temperature for AMS 4777 is 0.001 in. – 0.004 in. (0.03 mm – 0.10 mm).

The properties of a brazed joint are dependent upon numerous factors including base metal properties, joint design, metallurgical interaction between the base metal and the filler metal. Joint ductility, strength and high temperature properties, and alloy re-melt temperature, increase with increasing temperature and heating cycles, and decreasing joint clearances. The hardness decreases, due to diffusion of the boron onto the base metal and greater brazing-alloy/base-metal alloying.