I very would really like to check out how this rpeiar progresses. It is normally a challenge to accomplish a weld rpeiar over a non-ferrous cast element. Cleanliness is indeed the critical, not only the element but also the tools employed to prep the welds, the cleaning solutions etc. etc. I employed to need to rpeiar a magnesium gear case on a J-57, plus the trouble was the casting is as you reported, impurities both of those while in the constituent metal and impurities such as lubricating oil and grime that have soaked into the component in excess of the many years. A good soaking in an oven can enable to bake out some of the crud, but as well often the mistake is manufactured to media blast the element which only adds much more impurities. And fantastic stage in that this block could not possess the appropriate alloys to lend itself to welding, (such as 6061, or 5052). I agree that a pre-heat and a pressure relief cycle is in order. Tough part about that is certainly there is no e-book on this, its a little something of an educated guess. Speaking of jet engines, we also had a machine that pre-heated and stress relieved welds on sizzling sections using ceramic coated heat blankets. Question if such a piece of equipment is offered for civilian markets?