Good evening. New to the forum. I’m relatively new to casting, but I come from a machining and fabrication background. More to the point… After a good deal of research, I can’t seem to find much info on backyard aluminum alloys. I’m hoping someone could give some insight and share their experiences with alloying their cast aluminum projects. Reasonably available materials like zinc, lead, magnesium, manganese etc. I have even kicked around the idea of trying out melting down some old chroma plated diecast faucet parts. Any info is much appreciated. Thanks.
dont do it! you are just opening yourself up to unnecessary failures, the most important alloying element for aluminum is silicon, and it has been discussed recently and often, it is difficult to get silicon into solution in aluminum because of it's much higher melting point 1,410°C for silicon , same holds true for copper in aluminum, they will not just dissolve into solution when the aluminum is at it's pouring temp 750 C, go hunt down some actual cast aluminum and start casting, dont set yourself up for frustration with mystery metal V/r HT1 P.S. the diecast plumbing parts are probably not aluminum at all but rather Zamak (zinc)
Thanks for the input. Zamak is a useful and reasonably strong material, is it not? I figure as long as I keep like material together, can’t be anything too catastrophic. I’ve got plenty of cast, but I’ve got a lot of other stuff that seems to be worth tinkering around with.
I can't speak to the solubility of silicon but copper does readily dissolve into molten aluminum, I found that out by accident in a failed attempt to embed a copper cooling coil into a cast aluminum heatsink.
That's probably because it's not worth it. The first question is why do you want to do so? The usual answer is because I have all this wrought or extruded stock. Sell or trade it for casting stock at the scrap yard, you'll be miles ahead. One possible exception is casting machining blanks, but most hobbysts are unlikely to achieve wrought properties in the resulting billets when doing so, at least in aluminum. The biggest problem can be knowing what alloy you have to start with and even if you do, it's unlikely you'll make a more suitable casting alloy (or know if you have) than just using recycled castings. Silicon is one of the more common materials added to enhance fluidity. It is soluble in aluminum but not as readily as many other metals. When you buy it from metal suppliers that cater to the casting industry, most of the time it will be offered in 50Al/50Si% waffle chips which much more readily dissolve in aluminum melts. Silicon is relatively expensive and you will likely discover it is cheaper to buy casting alloy or scrap than it is to try to buy and add Si to extrusions or wrought stock......and the less expensive FeSi lump is a poor substitute because though iron can have some enhancing affects at very low levels, it will subatantially degrade mechanical properties of aluminum in relatively low concentrations. Still, if you must, a slightly more practical thing to do is add a high silicon alloy to wrought or extruded stock. Cast engine pistons can have higher Si content, but you need to have a source for them and know the difference between cast and forged pistons and even so, Si content can vary quite a bit. At best you'd probably only be able to use 1lb of wrought per lb of piston. Grain Refiners and Modifiers are another discussion but only really apply to AlSi alloys. Best, Kelly
While I do have a lot of extrusions and 6061 drops/leftovers, my primary concern is with zinc and magnesium, as I understand they add toughness. Maybe lead for weight and density. I’m looking at taking up a Gingery-style lathe (with some modern upgrades) to refine my mold making and such. So trial and error is to be expected. Plus having a lathe on hand would drastically help with some future projects I have in mind. thanks for the in-depth response.
I've both built a Gingery lathe and experimented with adding copper to high silicon piston casting metal. I think experimentation is fine if you want to "see what happens" when you try something. On the other hand it's an experiment, not a certainty, and possibly a long shot that you will see an improvement. The main reasons for a lack of improvement are that you don't know precisely what you have as alloyed metal stock begin with, so your new alloy is unknown, and a lot of named alloys are very specific in requirements. Minute quantities make a difference. So do impurities. So does aging and tempering. And you also need to have some way of measuring any improvement. If not it's just a belief that stock was improved. Anyway, most of us are in this for fun not profit, so sure, why not try something you are interested in? You might learn you don't want to repeat it, but hey, then you learned that. No real loss. And it's not absolutely impossible that you won't see an improvement. As for the Gingery lathe, you absolutely don't need a high grade of aluminum to build one, because every part is way over-built for its scale and function. Most castings are 1/2" or more thick. This is a small lathe, suitable for a 1/4 to 1/2 hp motor and the ways are steel. You will not be able to break any part of it in normal use. It you drop the whole thing onto a concrete, floor maybe. If you absolutely insist on more strength, forget any type of cast aluminum, and build it in Zinc/Zamac. It approaches steel in strength, and is stronger than CI. And if absolutely determined, use purchased virgin Za-12. But you will find zinc in general very difficult to work with without a mill. As a first lathe build, lacking a mill, I'd recommend only doing the half-nut in zinc alloy, and the rest of the castings in aluminum. Then the main wear point in the lathe is zinc (a good tough bearing material) and the rest is easy to work aluminum.
