Welding Tips and Tricks

Hey guys. I'm more of a reader than a poster but I've been stumped today.

I've had an original 1961 Lambretta TV175 Horncasting come in for repair on a large crack but I cannot find information about the type of aluminium used in said casting. It's colder than 4043 should usually feel in my shop and has a much sharper ring when struck.

If any of you know what it is then awesome, what is it?! lol
Failing that, what do you suggest is the best selection for an unknown alloy? I was thinking 4043 as thats generally seen as the best option for unknown castings however it is only 2mm thick so if anyone has a different suggestion which may provide a little more flexibility in the joint after repair then please, suggest away.

Thanks in advance,
Jonty

Actually, nevermind, I think I've just discovered that it's a zinc casting so a repair is highly unlikely unless it can be reliably brazed. It's not structural or safety related so a braze might work. What do you think?

perhaps this might work?

I've used HTS2000 for things like this & had good results - only down side is it goes almost instantly from solid to near water consistency so can be hard to control - you can't readily build up things for reinforcement on a repair without making some sort of perimeter enclosure - strength wise it's amazing & it bonds with almost any alloy.