Porosity on silicon bronze cast iron brazing

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Tried practicing some SIB braze on cast iron, and got massive porosity.Made some coupons out of an old brake disk, cleaned off most of the rust by soaking in phosphoric acid and hit the belt sander to give a bevel.First try was DC, 150A and the top of the bead didn’t look terrible, sure had some holes.Tried AC on the other side, 10% cleaning and that was a disaster. It seemed to pull all sorts of crap out of the cast iron and contaminate the tungsten right away. Gave it a break test and OMG, whole thing full of holes.One guess is I didn’t clean the middle lands where the parts touched, and they still had the black phosphate from the acid clean, IDK, maybe this was contaminating the weld???So what settings do you guys like for cast iron TIG braze? Here’s the disastrous first attempt:




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Reply:Never had any bgreat luck with tig brazing cast iron. Gets to hot too quick and cools too quick. Brazing cast is a slow process of bringing up to temp and getting penetration as it wicks into the crack and wets out in the pores then cools slowly since large area is brought up to high temps. It doesn't really take to the casting when casting is only heated locally with tig.  Oxy-Acetylene is more user friendly for brazing cast.