There is a special kind of solder that sticks well to non-ferrous alloys. It's melting temperature is about 300 F degrees less than aluminum and will join dissimilar metals very well. It takes some practice to be good at using it because it doesn't stick very well unless you are just below the melting point for aluminum. Just a little too hot and everything quickly turns into a blob. I saw some of this solder in the JCWhitney catalog, but couldn't find it just now. It's there somewhere. Walt Tampa, FL