I feel a need to share some of my experiences with cast aluminium, this will be only personal views, not aimed at anyone or trying to spoil anyones fun in trying to make your own as I am all for having a go at something and f@&king it up and trying again as sometimes this is the best way to learn!

Cast aluminium will always be full of aero holes, I once tried to water cool a vacuum forming tool that was made out of 20 chocolate box female aluminium castings which were cast by a foundry that specialized in aluminium. After 40 hours of drilling 1mm holes and then linking all the holes by back drilling the castings then free hand milling all the tracks to link the holes and then mounting them on a nice solid 1" aly plate found out that after I had water tested it that I had made myslef a very expensive and very large water sprinkler!

Threw it straight in the scrap bin and started again, tried it a couple of times again with different grades and methods of cast aly with same results. In the end I gave up and watercooled the 1" extruded aly back plate by drilling and plugging, never bothered with water cooling the castings again.

Personally I don't think you can cast ally without aero bubbles, I may be wrong but would take a lot of convincing!

By the way just bought some T6 aly plate today - £39.70 for a piece of 550x300x20mm. I have not had the fun of making it but can have more fun machining it and for £40 I know what I would rather be doing.....

Still interested to see your results though.