Aerospace brazing and brazing alloys.

Aerospace brazing may be used for repairs to primary aircraft structures only if brazing was originally approved for the particular application. Brazing is not suitable for repair of welds in steel structures due to lower strength values of the  brazed joint as compared to welded joints. Brazing may be used in the repair of secondary structures.

Brazing alloys.

Due to the large number of brazing alloys used, it is difficult to be certain that the material selected for repairing a brazed joint will result in a joint having the  same strength characteristics as the original. In cases where it is necessary to apply copper alloy brazing material, more than once on a steel surface, and particularly if temperatures over 2,000° F. are reached, there is a possibility that brazing metal may penetrate between the grains in the steel to an extent that may cause cracking. Copper brazing of steel is normally accomplished in a special furnace having a controlled  atmosphere, and at a temperature so high that field repairs are seldom feasible. If copper brazing is attempted without a controlled atmosphere, the copper will probably not completely flow and fill the joint. Therefore, in aerospace applications, copper brazing in any other than appropriately controlled conditions is not recommended.