Strengthening Aluminum (casting mix)

[Curl]

I want to cast a part out of Aluminum (from scraps). Is there anything I can throw into the melt mix to make it come out stronger (not as gummy and soft) ??

Some sort of ceramic I'm thinking? Very fine sand-like stuff (e.g. CaCO3)?

Any suggestions for heat treatment too? The part will be a shell-type housing, needs to be strong and stiff.

[Astronuc]

See - Aluminum Alloys – Effects of Alloying Elements
http://www.keytometals.com/page.aspx?ID=CheckArticle&site=ktn&NM=55

See also -
http://www.keytometals.com/page.aspx?ID=Articles&LN=EN#p2

Look under +The Basics of Nonferrous Metallurgy

There's a number of articles on Al and alloys.

[Curl]

Good stuff.

So if I add some Iron to the mix, how should I cool in order to keep a homogeneous (as close as I can) mixture after hardening. I don't want to form a distinct two phase composite, as I suspect it will lead to crack formation.

What is it talking about here:
"The solubility of iron in the solid state is very low (~0.04%) and therefore, most of the iron present in aluminum over this amount appears as an intermetallic second phase in combination with aluminum and often other elements."

[Mech_Engineer]

What kind of aluminum scraps are you using? If it's pure aluminum, you can add the components necessary to form a higher-strength alloy like 6061 or 7075. Then after casting, you can apply a heat treat like -T6 or -T651 to get the most stength you can out of it.

If its a mix of different aluminum alloys you don't know, well you'll basically be stuck with what you get...

[Curl]

It is most likely going to be 6061 heat treated aluminum scraps.

And how should the heat treatment go in order to get highest strength? I remember doing this in a lab at some point but I forgot it completely.

[cloa513]

Solution heat treat at 990 F for adequate time to allow for thorough heating and then water quench. Precipitation hardening is done at 320 F for 18 hours and air cool, followed by 350 F for 8 hours and air cooling.

Its easy to find by googling 6061 heat treatment.