Can't really see a reason to weld the dissimilar metals together? That would be highly specialised. One is a aluminium based alloy, The other iron based. I've repaired a few cast Ali/iron heads for cars/drag cars before. Fully F/G clamped the head to a 2" thick cast iron milled table. Pre heated with the oxy gently/the entire head gradually. Grooved out the crack with Ali Burr on the die grinder, down to where you can't see where the crack started, welding well before where the crack started and finished using cast Ali rods and pure argon. Post heated the head gradually to a cool down. The heat transfer properties and molecular structure of the materials are pretty much a polar opposite. Alloys are loose softer and dance freely, high thermal expansion and contraction. Irons are tighter don't dance and have low thermal expansion and contraction. Alloy's s are a/c welding with tig for castings. Iron's Are d/c - welding with tig for castings. They both have a tendency to spit the filler material out if you weld it too hot, that's where the pre and post heating comes into it. I crank the hot start up a bit because you will create a weak point if you hang around to get the weld puddle pooling. Easy on Ali harder for lower amps on cast. Nature of the beast. The pre-post heat is more critical on the alloy than iron. Just a thought? Our new Kempi tig has a mix setting that combines Ac/dc current and has a synergic setting as well? Can't beat the old analouge Hobart welder so far as I'm concerned. Digital, high low high low, analouge higgghh lowww, higgghh, lowww. Makes for beautiful pulse welding! Alternatively you could mash a heap of bird shit into the corner and hope the flux and slag sticks it togetherB-) bronzing, brazing, solder, pop rivets, silicone. Nuts and bolts etc:-)