For those of you that are serious about metal casting as a hobby avoid extruded, die cast, plate and structual. Some of my favouit alloys are automatic trnsmission cases, engine blocks, cylinder heads, rims, hydraulic pumps, outobard marine engines.
Some of the above alloys have resistance to abrasion, some to errosion with the high silicon alloys able to fill the most intricate cavitys like the air cooled fins small air cooled engines.
After removing dross I use a deagassing tablet just befor pouring the metal into the sand mold, always arrange your core box so that the bottom side is topside. This way any small bits of dross going into the pour will make a small imperfection on the non usualble side.
On my fishing weight molds had these imperfections showed up on the inside where the finish of the lead casting is criticle the casting woiuld have to be discarded. Imperfections on the backside are easily cleaned up.
Foundrys use ceramic filters during the pour to keep out contaminants from entering the mold.
This SCUBA weight mold would have been poured with the bottom side up keeping the inside free of imperfections.
Message for the OP I have made serveal posts on this topic which you may find of interest http://www.scrapmetalforum.com/metal-casting/
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