Coupla things you can check

1. is the crack *fully* (100%) routed out before you attempt repair?

2. Most Al is alloyed with Mag and most Mag is alloyed with Alum. Which do have? If you can get a word from the manufacture we can sort this out quickly.

3. you can take mag wire and weld it right into aluminum, than as it cools strike it with a hammer and the Mag. weld bead will often pop right out.. (its cute for keychains)

4. Since its just a lawnmower deck (and not the head) you might go on experimenting with mag. AZ101 is most forgiving. of the aluminum alloyed mags.. But maybe its not aluminum alloyed, in that case EZ33 might do the trick.

Have fun

Lawrence