Welding to the subframe.

[911monty]

First off you can not just "weld" the aluminum without knowing exactly what it is. Forged, heat treated or just cast require different welding techniques. Welding will change the metallurgy of the material near the weld from the heat. Aluminum is much more sensitive to heat than steel and can become brittle if not not done properly. Since this is a suspension component it is likely at least heat treated. You also stated that the suspension is being stressed under heavy load. Since the spot that has failed is directly where the control arm is bolted to and is in the middle of the support you can bet the forces are highest there. Now ask yourself, What would happen if this component fails during any aggressive driving?

[rusty69911]

those whole brackets are less than $100 on ebay, I paid that shipped to Australia as mine was missing all together, not a hard job to swap out