I bought a pack of these rods at Oshkosh a couple years ago. Works great for soldering up holes in soda cans. Tried to use it to repair an aluminum SCAT duct flange and could not get it to stick to that aluminum.
We actually repaired as skeg on my outboard motor with these, however we had to use an aceteline torch to get every thing hot enough. Ended up puddling the aluminum rod and the ground it all away to get the shape back. They are right it is much harder than aluminum
Jack