Liquid Film Migration During Aluminum Brazing

The effects are described in aluminum brazing of a phenomenon known as Liquid Film Migration (LFM). This is primarily encountered when -O temper parts are formed and subsequently brazed. If the combination of material homogenization, alloy and cold work is such that the material does not recrystallize totally before the brazing temperature is reached, then the system begins to equilibrate by rapid solid state diffusional processes. These create a moving liquid interface which sweeps from the clad/core interface into the core of the material. This causes significant compositional changes in the volume through which the liquid film passes. Reduced brazeability (filler metal flow) results from the rapid diffusion of silicon into the core. Additionally, a coarse band of intermetallics is formed upon solidification of the enriched liquid zone which can impair corrosion resistance.