Welded Samples

Hello "Guest". I have just noticed this plea for assistance and it's been sitting around for a few days.

Please understand that welding is NOT my field, nor is metalurgy so the following is only a guess, but might start some other discussion.

I suspect that what you are seeing is one of two effects.

My first guess is that the galvanic potential of the materials is causing the effect that you see where the AL-6XN is becoming like a sacrificial annode in the joined material.

The second guess is that the process of welding (heat induced) has caused local metalurgical changes in the materials that has made them susceptible to corrosion.

As I say, just a guess, but hope this helps.