# Lead/Aluminium Alloy? **URL:** \ **Category:** Factual Questions\ **Created:** [March 10, 2007, 2:07am UTC](https://boards.straightdope.com/t/lead-aluminium-alloy/395338 "2007-03-10T02:07:12Z")\ **Posts on this page:** 17\ **Page:** 1
**Author:** ![Full\_Metal\_Lotus](https://avatars.discourse-cdn.com/v4/letter/f/df705f/32.png) [@Full\_Metal\_Lotus](https://boards.straightdope.com/u/Full_Metal_Lotus)\ **Post date:** [March 10, 2007, 2:07am UTC](https://boards.straightdope.com/t/lead-aluminium-alloy/395338/1 "2007-03-10T02:07:12Z")
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? Regards FML ---
**Author:** ![Stranger\_On\_A\_Train](https://avatars.discourse-cdn.com/v4/letter/s/13edae/32.png) [@Stranger\_On\_A\_Train](https://boards.straightdope.com/u/Stranger_On_A_Train)\ **Post date:** [March 10, 2007, 2:19am UTC](https://boards.straightdope.com/t/lead-aluminium-alloy/395338/2 "2007-03-10T02:19:45Z")
Lead is added to aluminum to improve machinability ([cite](http://www.key-to-metals.com/Article55.htm)). Stranger ---
**Author:** ![Full\_Metal\_Lotus](https://avatars.discourse-cdn.com/v4/letter/f/df705f/32.png) [@Full\_Metal\_Lotus](https://boards.straightdope.com/u/Full_Metal_Lotus)\ **Post date:** [March 10, 2007, 2:28am UTC](https://boards.straightdope.com/t/lead-aluminium-alloy/395338/3 "2007-03-10T02:28:32Z")
[QUOTE=Stranger On A Train] Lead is added to aluminum to improve machinability ([cite](http://www.key-to-metals.com/Article55.htm)). Stranger [/QUOTE] Gah.. I feel so dumb! Thanks FML ---
**Author:** ![Bryan\_Ekers](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bryan_ekers/32/183_2.png) [@Bryan\_Ekers](https://boards.straightdope.com/u/Bryan_Ekers)\ **Post date:** [March 10, 2007, 3:13am UTC](https://boards.straightdope.com/t/lead-aluminium-alloy/395338/4 "2007-03-10T03:13:24Z")
Now an aluminum-_mercury_ alloy… that’d be something. A big puddle of goo, but _something_. ---
**Author:** ![Santo\_Rugger](https://avatars.discourse-cdn.com/v4/letter/s/e95f7d/32.png) [@Santo\_Rugger](https://boards.straightdope.com/u/Santo_Rugger)\ **Post date:** [March 10, 2007, 3:19am UTC](https://boards.straightdope.com/t/lead-aluminium-alloy/395338/5 "2007-03-10T03:19:52Z")
[QUOTE=Stranger On A Train] Lead is added to aluminum to improve machinability ([cite](http://www.key-to-metals.com/Article55.htm)). Stranger [/QUOTE] \ 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? ---
**Author:** ![samclem](https://avatars.discourse-cdn.com/v4/letter/s/a9a28c/32.png) [@samclem](https://boards.straightdope.com/u/samclem)\ **Post date:** [March 10, 2007, 3:25am UTC](https://boards.straightdope.com/t/lead-aluminium-alloy/395338/6 "2007-03-10T03:25:11Z")
[QUOTE=Pygmy Rugger] ETA: I think the OP was looking for an alloy with more than .5% lead? [/QUOTE] The OP thought that any mixing was impossible in Earth’s gravity. It evidently isn’t. ---
**Author:** ![WarmNPrickly](https://avatars.discourse-cdn.com/v4/letter/w/d78d45/32.png) [@WarmNPrickly](https://boards.straightdope.com/u/WarmNPrickly)\ **Post date:** [March 11, 2007, 6:16pm UTC](https://boards.straightdope.com/t/lead-aluminium-alloy/395338/7 "2007-03-11T18:16:21Z")
What does an alloy have to do with gravity? Its about solubility isn’t it? ---
**Author:** ![Sunspace](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/sunspace/32/1250_2.png) [@Sunspace](https://boards.straightdope.com/u/Sunspace)\ **Post date:** [March 11, 2007, 6:38pm UTC](https://boards.straightdope.com/t/lead-aluminium-alloy/395338/8 "2007-03-11T18:38:54Z")
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. 🙂 ---
**Author:** ![ElvisL1ves](https://avatars.discourse-cdn.com/v4/letter/e/5daacb/32.png) [@ElvisL1ves](https://boards.straightdope.com/u/ElvisL1ves)\ **Post date:** [March 11, 2007, 7:08pm UTC](https://boards.straightdope.com/t/lead-aluminium-alloy/395338/9 "2007-03-11T19:08:49Z")
Yes, it’s all about the elements’ solid solubility in each other, not their densities. [ASM](http://www.asminternational.org/asmenterprise/apd/AdvancedSearchAPD.aspx) 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. ---
**Author:** ![WarmNPrickly](https://avatars.discourse-cdn.com/v4/letter/w/d78d45/32.png) [@WarmNPrickly](https://boards.straightdope.com/u/WarmNPrickly)\ **Post date:** [March 11, 2007, 11:02pm UTC](https://boards.straightdope.com/t/lead-aluminium-alloy/395338/10 "2007-03-11T23:02:53Z")
Could be that there is more to this than meets the eye. > [@](#): > > On Earth, when a melted alloy solidifies, it forms pine-tree-shaped crystals called dendrites. These dendrites play a very important role in determining the properties of the alloy and its subsequent usefulness. Gravity causes fluid flows in the alloy, leading to the formation of irregular dendrites that weaken the alloy or metal structure. This type of processing is so complex that it is difficult to measure and predict, and even more difficult to control. In space, gravity-related phenomena such as convection are reduced, thus simplifying the process for study. from [here](http://www.nasa.gov/centers/marshall/news/background/facts/microgravity.html) ---
**Author:** ![ElvisL1ves](https://avatars.discourse-cdn.com/v4/letter/e/5daacb/32.png) [@ElvisL1ves](https://boards.straightdope.com/u/ElvisL1ves)\ **Post date:** [March 11, 2007, 11:17pm UTC](https://boards.straightdope.com/t/lead-aluminium-alloy/395338/11 "2007-03-11T23:17:54Z")
\*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. ---
**Author:** ![WarmNPrickly](https://avatars.discourse-cdn.com/v4/letter/w/d78d45/32.png) [@WarmNPrickly](https://boards.straightdope.com/u/WarmNPrickly)\ **Post date:** [March 11, 2007, 11:33pm UTC](https://boards.straightdope.com/t/lead-aluminium-alloy/395338/12 "2007-03-11T23:33:16Z")
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. ---
**Author:** ![ElvisL1ves](https://avatars.discourse-cdn.com/v4/letter/e/5daacb/32.png) [@ElvisL1ves](https://boards.straightdope.com/u/ElvisL1ves)\ **Post date:** [March 12, 2007, 11:14pm UTC](https://boards.straightdope.com/t/lead-aluminium-alloy/395338/13 "2007-03-12T23:14:52Z")
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. ---
**Author:** ![WarmNPrickly](https://avatars.discourse-cdn.com/v4/letter/w/d78d45/32.png) [@WarmNPrickly](https://boards.straightdope.com/u/WarmNPrickly)\ **Post date:** [March 13, 2007, 12:33am UTC](https://boards.straightdope.com/t/lead-aluminium-alloy/395338/14 "2007-03-13T00:33:19Z")
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. ---
**Author:** ![ElvisL1ves](https://avatars.discourse-cdn.com/v4/letter/e/5daacb/32.png) [@ElvisL1ves](https://boards.straightdope.com/u/ElvisL1ves)\ **Post date:** [March 13, 2007, 12:40am UTC](https://boards.straightdope.com/t/lead-aluminium-alloy/395338/15 "2007-03-13T00:40:48Z")
[Wiki’s is a pretty decent summary](http://en.wikipedia.org/wiki/Phase_diagram). 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. ---
**Author:** ![Booker57](https://avatars.discourse-cdn.com/v4/letter/b/b9e5f3/32.png) [@Booker57](https://boards.straightdope.com/u/Booker57)\ **Post date:** [March 13, 2007, 2:41am UTC](https://boards.straightdope.com/t/lead-aluminium-alloy/395338/16 "2007-03-13T02:41:29Z")
[QUOTE=Sunspace] 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. 🙂 [/QUOTE] You supply the Gold, I’ll supply the Aluminum 😃 ---
**Author:** ![Sunspace](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/sunspace/32/1250_2.png) [@Sunspace](https://boards.straightdope.com/u/Sunspace)\ **Post date:** [March 13, 2007, 3:00am UTC](https://boards.straightdope.com/t/lead-aluminium-alloy/395338/17 "2007-03-13T03:00:41Z")
[QUOTE=Booker57] You supply the Gold, I’ll supply the Aluminum 😃 [/QUOTE] Just a moment… :: digs for [change](http://boards.straightdope.com/sdmb/showthread.php?t=409463) ::