We just had a failure from our vacuum braze process. The braze cycle is good as is the vacuum and temperatures. However, there was no brazing to be had. The core literally was disassembled showing that the 4004 braze sheets were fully intact. This indicated to us that it was in fact not claded brazing sheet at all. The supplier has been contacted and indicates that yes the material is 4004 claded sheet.

My thoughts take me to a test I have used to determine if a dock-plate (in need of repair) was Aluminum or Magnesium. A drop or two of liquid silver solder flux will turn black indicating Magnesium. Alternatively if it stays clear indicates Aluminum.

Is there a test with some sort of solvent to check for the cladding?