Lead/Aluminium Alloy?

Here on Earth, a lead aluminium alloy is impossible as they separate, rather than mixing (due to differences in weight/density) in our gravity.
Could a led aluminium alloy be produced in zero gravity? Any ideas of what its properties would be?


Lead is added to aluminum to improve machinability (cite).


Gah… I feel so dumb!

Now an aluminum-mercury alloy… that’d be something.

A big puddle of goo, but something.

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From what I understand, lead becomes a lubricant, because it “smears” while the part is being machined.

ETA: I think the OP was looking for an alloy with more than .5% lead?

The OP thought that any mixing was impossible in Earth’s gravity. It evidently isn’t.

What does an alloy have to do with gravity? Its about solubility isn’t it?

My friend has a “Scientific American Cyclopedia of Receipts” from 1913 or so–a big book of instructions on how to make everything from soap to cola to steel–that has instructions on how to make an alloy of gold and aluminum that is apparently purple. I want him to make some. :slight_smile:

Yes, it’s all about the elements’ solid solubility in each other, not their densities. ASM has a great index of phase diagrams. Can’t link directly, but the Al-Pb diagram shows they have complete solubility in each other at all compositional percentages. It’s therefore not only possible but *easy * to make a lead-aluminum alloy, and in any ratio you like.

Could be that there is more to this than meets the eye.

from here

*Any * fluid flow in the alloy will break off dendrites, whether originating in gravity or convection or uneven cooling or whatever. Your cite is correct in suggesting that they’ll get bigger before breaking off in the absence of gfavity-induced convection, though.

Dendrites only get to be an engineering issue in incompletely-soluble phases, where liquid metal is unable to reach the spaces between the “branches” before freezing off, leaving voids in the solid material. But there’s no such phase in the Pb-Al binary system.

Dendrite *formation * (as opposed to breakage) is entirely a function of crystal lattice structure and the 2nd Law of Thermo, not gravity, anyway. Atoms from the melt fit themselves into the growing lattice at the minimum-potential-energy positions, and the result (for cubic structures like most metals form) is a bunch of little protrusions at right angles to each other, looking like little trees.

I guess I’ll have to take your word for it on the Pb-Al phase diagram. They are univeersally soluble at all temperatures? I am having difficulty imagining what the phase diagram woulde look like with all temperatures included. It must be a 3d graph.

Notice I know nothing about alloys so I’m not questioning you except to learn.

Yes, Pb and Al are fully soluble in each other at all composition ratios and all temperatures.

Try this: A binary phase diagram has composition (0-100%) along the bottom, and temperature up the sides. A fully-intersoluble pair just has a single curved line across the graph, showing the melting point of the alloy vs. composition. Mix molten lead and molten aluminum together in any ratio you like, let it cool, and there will be a single defined temperature at which it transitions from a fully-mixed liquid to a fully-mixed solid. Heat it back up, and at that same temperature it will transition back to a fully-mixed liquid again.

A phase diagram for a partially-intersoluble material combination has a lot more lines and a lot more phase regions defined, including the transitions to intermediate “mushy” phases where dendritic growth occurs (and lots of other things get complicated too). But that’s tough to explain in a text-only post, so please be merciful.

Gotcha. It’s been a long time since I’ve seen a phase diagram. So % composition on bottom (X) and temp is the Y axis. I don’t suppose you could point me to some examples on the web could you? I vaguely remember a cummulative exam that had something to do with these. What is a eutectic mixture? That word just creeped into my brain.

Wiki’s is a pretty decent summary.

A eutectic mixture is the “sweet spot” in a partially-intersoluble composition where there’s a direct solid-liquid phase change, no mushy alpha or beta phases.

You supply the Gold, I’ll supply the Aluminum :smiley:

Just a moment…

:: digs for change ::