Aluminum 6061 weld cracking with improper filler wire selection

Tom develops the textbook case (from Sindo Kou) of 6061 base metal welded with 1100 filler producing a wide freezing range and consequent cracking — the central teaching example for heat-treatable aluminum weldability.

To give you an idea of some of the cracking you get — this comes out of Sindo Kou's book. The first one is 6061 where they used 1100 filler metal, and I'll explain why this is a problem. The reason it's a problem is 1100 filler metal is nearly pure aluminum, and the 6061 is highly alloyed as a precipitation-hardenable alloy. If you look at the phase diagrams for aluminum, almost all of them start out as some eutectic. This is aluminum-magnesium-silicon, so it's magnesium and silicon added to the alloy. This is temperature. This is a phase diagram. We've got liquid up here.