Joe Gandalf fired this volley in
:

So, should I (or, more likely, the shop I take it to) still use the
pure Mg rod, as the manual suggests?


Yup... just lotsa-lotsa inert gas and a low enough amperage so that you
can have the weldment cool enough before leaving the gas shield.

Magnesium is fine for welding magnalium; though not quite as strong.

The aluminum was originally added simply because magnesium alone doesn't
pressure-cast very well without crystallizing (fractures), and doesn't
have the tensile strength of magnalium. The aluminum makes the mix more
plastic.

Lloyd