[rowow]

I want to cast some 6061 aluminum round/bar stock for my lathe and soon to be built cnc machine due to the obvious cost savings. However after a test melt on some quality 6061 aluminum extrusions into a rough rectangle, I put the cast on my lathe and cutting it came out very poor. The texture was just awe full compared to a factory extruded round stock, or even round stock from melted aluminum rims/wheels. What is causing this softness and poor quality? Do I need to harden it through quenching? How could I get the same or similar quality to extruded 6061?
I was looking at flux and degassing would that help? And whats the purpose of flux (degassing is obvious)? Does anyone have any cheap alternatives/substitutes to flux and degassing that I could buy locally or online if needed.

[awerby]

Extruded aluminum and cast aluminum use different alloys. Melting down old castings will give you better results than melting extrusions. If you don't provide enough riser (which seems to be the case with that ingot you made), then the resulting billet will be porous. Flux is necessary; degassing helps a lot. Bad results in turning are probably due to lack of heat treatment; raw aluminum tends to be extremely gummy, and doesn't machine well at all. But if all you want is round stock for turning, try to find some drops of factory-made 6061 t6 round rod; it's going to work better than anything you cast and try to heat-treat yourself, and it's not really that expensive, considering.

[rowow]

Extruded aluminum and cast aluminum use different alloys. Melting down old castings will give you better results than melting extrusions. If you don't provide enough riser (which seems to be the case with that ingot you made), then the resulting billet will be porous. Flux is necessary; degassing helps a lot. Bad results in turning are probably due to lack of heat treatment; raw aluminum tends to be extremely gummy, and doesn't machine well at all. But if all you want is round stock for turning, try to find some drops of factory-made 6061 t6 round rod; it's going to work better than anything you cast and try to heat-treat yourself, and it's not really that expensive, considering.

What do you mean by riser? As for costs a 6" round stock 4 inches length can cost around $50 and only cost $5 in scrap aluminum. I am also using a electric foundry which runs about $1 a hour in electricity and takes 30 mins to melt around 40lbs of aluminum. AKA its cheaper no matter how you look at it.
But ill try flux and degassing then heat treating, but do you have any recommended cheap flux/degassing that I can get locally? And what exactly does flux do?

[beone]

Cast 6061 will not have the same characteristics as bar due to it not being cold worked. As cast it is brash and works poorly. You can improve it greatly by heat treat. Six hours or so at 400 to 450 farienheight will make it machine much better. Your normal oven will work fine.

[RotarySMP]

To solution heat treat 6061 back up to the T6 hardness, you need to take it up just under the melting temp, to 980°f, hold for about an hour (depending on cross section) and then rapidly quench it, followed by artificially age hardening it for more hours at lower temps.

Can your electric furnace control temperature within 5-10°? That would be great for heat treament.

Aluminum Workshop: Achieving T6 designation for 6061 - The Fabricator

I have tried Beone's suggestion of only artificially age hardening some of my castings, but found it ineffective. The samples I compared were just as nasty and gummy to machine before and after.

A mix of sodium and patassium chorlide (table salt and light salt) is supposed to work for degassing, but never worked well for me. Then again I started controlling temp with a punge pyrometer at the same time as maknig a degassing lance for argon. Together they greatly reduced porosity.

Flux is supposed to aid the separation of the oxides from the molten metal. Wash soda (dry it first) is supposed to work. Havent seen much beefit from it myself. If you raw stock is at all dirty of painted/anodised etc, I get better ours by first pouring ingots and then remelting for castings.

Are you on AlloyAvenue network. That is the best hobby casting forum.
Mark

[rowow]

Yes my electric furnace can control the temperature but I dont know how accurate (since I made it myself) but ill try to getting it as close as possible. And thank you so much for the detailed answer and the links, you answered exactly what I needed, now all I have left is to testing some melted aluminum. As for AlloyAvenue, I am on it but when searching for aluminum flux information I found alot more posts on this website so I thought I could get more information here. But agian thank you for all the help, I had alot of confusion due to mixed information and was worried I would mess things up.

[awerby]

It seems that most of your questions have been answered. But if you buy aluminum drops as scrap, they don't cost nearly that much. A riser is a volume of metal that feeds the casting as it shrinks. You want to design one that's thicker in section than the casting it's feeding, so it stays hot longer.