This is plating to prevent corrosion, due to cathodic "sacrificial corrosion" of the Zn and Al, which are higher in the electrochemical series and
also resist corrosion themselves through forming thin oxide layers which unlike Fe2O3 or FeO(OH) are impervious to further attack by atmospheric O2.
See http://www.key-to-metals.com/Article21.htm
If I recall correctly, there are a number of zinc/aluminum alloys, many of which are known as pot metal or white metal, think carburetor or metal toy.
Zamak is the name of at least one of them that also has magnesium and copper http://en.wikipedia.org/wiki/Zamak
[Edited on 16-5-2006 by urbs]Eclectic - 16-5-2006 at 09:14
Is it my imagination, or did the second post answer the question allready?12AX7 - 16-5-2006 at 16:57
If you'd like to get more particular about how completely you can check this: http://web.met.kth.se/dct/pd/element/Al-Zn.html
-They aren't very soluble solids much under the melting point, but the liquids are infinitely soluble.
Timenhzflep - 16-5-2006 at 20:46
Quote:
-They aren't very soluble solids much under the melting point, but the liquids are infinitely soluble.
Infinitely miscible?12AX7 - 16-5-2006 at 22:01
..Whatever...Zinc - 21-2-2007 at 11:06
A little OT but does molten zinc dissolve steel?not_important - 21-2-2007 at 13:20
Quote:
Originally posted by Zinc
A little OT but does molten zinc dissolve steel?
Very little. You would need t oworry if your are building factilities that will have those conditions day in and day out, for months or years.
Otherwise it's not really a problem, remember that galvanised iron/steel is a zinc coating on the ferrous metal, often put on by passing the iron
through a bath of molten zinc.12AX7 - 21-2-2007 at 16:07
No, actually it dissolves quite a bit. Let me dreg up a phase diagram here...ah.
Galvanizing consists of a layer of zinc on top of several extremely thin layers of intermetallics (as shown), depending on process. Hot dip
galvanized steel is going to have a thicker diffusion/dissolution layer and an equilibrium amount of zeta phase in the zinc coating, while
electroplated stock may have a diffusion region of, I would SWAG, a few hundred nanometers (more if heated at some point in processing).
It is very easy to dissolve through tin cans, even with a layer of iron oxide, when melting zinc.
Interesting to note that zinc is so soluble in alpha iron (ferrite). I wonder what the characteristics of such a "steel brass" would be; probably
harder than ferrite, and able to be precipitation hardened much the same as aluminum (indeed, about the same temperature even). Large amounts of Zn
reduces gamma-Fe (austenite), which should reduce the influence of carbon, as martensite can't(?) form on quenching the absent austenite. (Something
this rich in Zn is probably uselessly hard and/or brittle though. Maybe some nickel would mellow it out.)
Timnot_important - 22-2-2007 at 04:00
Interesting. I based my comments on two things.
The first was when I was trying to grow metal whiskers. I'd used junk bits of pipe to make a J shape, with the short arm capped and with a small tube
for feeding in N2, the longer arm had a close fitting ceramic tube insert and a small vent. It was held in verted, with zinc in the short arm which
was in a small furnace; the long arm was just out in the air. When I was done I'd unscrew the short arm, invert it in a large clay pot, and heat it in
the furnace to melt the zinc, then use tongs to remove the pipe from the zinc.
The pipe interior was well galvanized, but didn't seem to be really chewed up, although I wasn't paying much attention to that area. The zinc didn't
look odd, and it melted about where expected, but it was just cheap alloy grade metal.
I never ran much above the melting point of zinc, furnace limitations. It is likely I was below the melting points of most if not all of the mixed
phases. But there were runs where pure zinc should have been molten, and if it were a good solvent for iron and the mixed phases I would expect some
visable damage to be done to the pipe. Could some ofthe mixed phases be less soluble in zinc, and formed a protecting layer? The pipe was much
thicker than a tin can, but if it were really soluble I'd expect to have seen the inner surface chewed up.
The second item behind my comments is that zinc's cousin mercury is a very poor solvent for iron. Mercury is shipped in iron flasks, power plants
boiled mercury in ferrou alloy tubing. So I extrapolated from that and my experience with zinc.
There might be a practical problem with iron-zinc alloys. Given the high vapour pressure of zinc, the lost of it during melting, casting, and working,
might make it difficult to maintain tight control of the alloy composition, and to uneven product quality.12AX7 - 22-2-2007 at 08:53
Ah, understandable.
Metallurgically, zinc resembles aluminum quite a bit. They are completely miscible, and completely soluble in solid solution just below the melting
point (the phases seperate at lower temperature however). They do not form an intermetallic.
Zinc also resembles metals in its row, such as gallium, copper, nickel and iron; however, because it's so much more like aluminum (probably due to the
behavior of its electrons, being seated at the end of the d-block), it tends to fit in less well. Brass, for instance, is a solid solution up until
about 25% zinc, where a beta phase starts to form because the alpha phase can't tolerate any more stress (since Zn atoms are a little larger(?)).
This is explained nicely here.
I once attempted to produce zinc oxide by boiling zinc in the end of a pipe. I took a piece of 1.5" pipe and welded a plate to the bottom. I melted
zinc in it in the furnace and attempted to blow combustion air in, but I got little more than aerosol out. Afterwards, I noticed that the zinc was
rather well caked on. In fact, that caking survived quite well even having cut off the end of the pipe to use the sealed portion as a crucible with
my induction heater. Eventually, I cleaned that crucible with HCl, revealing a craggy surface (in part due to Zn intermetallics and also due to
scaling from generally being orange hot in a pure air atmosphere).
TimZinc - 21-3-2007 at 07:26
A little OT but is copper soluble in molten Al?
Also what is the melting point of a mixture containing 60% Al and 40% Cu?
Does it still have a golden collor?12AX7 - 21-3-2007 at 08:16
10%wt Al, 90%wt Cu looks like a light brass. I would imagine pure gamma is silver.
Theta is about 50/50 by weight (Al2Cu) and has about the same melting point as aluminum. Aside from the nature of it obviously being an intermetallic
(with all its appearance, habit and mechanical properties), it looks about like aluminum.
TimZinc - 21-3-2007 at 08:28
What is the melting point of the 10% Al and 90% Cu?12AX7 - 21-3-2007 at 10:16
Not much below Cu's.
If you want to cut the amount of copper to make it cheaper or lower-melting, the best you can do is yellow brass circa 35% (on the verge of white
(beta) brass), melting point about 1600F (870C).
TimZinc - 21-3-2007 at 10:23
Would lead brass have a lower melting point than the aluminum version?
Also what would be the minimum amount of copper that it should contain to remain golden collored?12AX7 - 21-3-2007 at 13:15
Lead does not dissolve very well in copper. With processing and technique, you might end up with what would be better called a composite, copper
particles soldered together by lead. If the surface has a smooth layer of copper (perhaps produced by etching (with dilute HNO3) and burnishing), you
could get a copper color with a low softening point (that is, a "mushy" state, not actually molten).
What's it matter, anyway? Copper and bronze are easy to melt in a furnace.
TimZinc - 21-3-2007 at 13:40
Quote:
Originally posted by 12AX7
What's it matter, anyway? Copper and bronze are easy to melt in a furnace.
I don't have a furnace and I still don't have all the materials and equipment to build one.12AX7 - 21-3-2007 at 20:22
Geesh, even African natives have the materials, just where are you? The Moon? Wait, no...
TimZinc - 5-5-2007 at 02:26
How about a mixture of Zn and Mg instead of Al and Mg? Would it be also very brittle? Also in the ratio 50:50.12AX7 - 5-5-2007 at 08:47
Yes. The Zn-Mg system contains the brittle laves intermetallic, Zn2Mg, which is 15.7% Mg by weight.
As I recall, most of the other intermetallics aren't as brittle, and the regions containing pure metal are varying degrees of hardness and strength
(ranging from malleable pure metal to strong, hard alloy to brittle intermetallic-rich compositions). It is similar to the Al-Mg system's behavior,
but contains more intermetallics and in different ratios.
View it as an easy way to pulverize zinc that has slightly more reactivity.
TimZinc - 7-5-2007 at 12:53
Quote:
Originally posted by 12AX7
Yes. The Zn-Mg system contains the brittle laves intermetallic, Zn2Mg, which is 15.7% Mg by weight.
View it as an easy way to pulverize zinc that has slightly more reactivity.
Tim
So it can be pulverised in a mortar and pestle as magnalium can be?
Also can I use the magnesium from pencil sharpeners to make the alloy or is it not pure enough? I have mixed powdered pencil sharpener with sulfur and
ignited it and it burned very fast like when I mixed pure Mg powder with sulfur. I read somewhere that pencil sharpeners are made of a alloy of
magnesium and aluminum but I belive that the one I have is pure Mg. Does the alloy of magnesium and aluminum become dark after some time (the pencil
sharpener is very old)? Also is the alloy magnalium or some other aluminum-magnesium alloy? I don't think that it is brittle as magnalium.
[Edited on 8-5-2007 by Zinc]12AX7 - 8-5-2007 at 13:50
Pencil sharpeners...magnesium!?? That makes no sense, they would use hardened steel for the cutting edge.Elawr - 8-5-2007 at 17:04
I have a concrete float which is apparently made almost entirely of Mg. These are available at the hardware store for around $20 as Magnesium Float.
Basically a rectangular slab of lightweight metal with a wooden handle, to use for smoothing out wet concrete.Zinc - 9-5-2007 at 03:18
Quote:
Originally posted by 12AX7
Pencil sharpeners...magnesium!?? That makes no sense, they would use hardened steel for the cutting edge.
The blade if made from steel. But the other part is probably made from Mg.Eclectic - 9-5-2007 at 03:31
More likely a Zn based "pot metal". Mg castings make no economic sense for a pencil sharpener.DrP - 9-5-2007 at 04:59
Quote:
Originally posted by Eclectic
More likely a Zn based "pot metal". Mg castings make no economic sense for a pencil sharpener.
Quite.. Also, I'm sure ALL of the school kids would have a field day setting fire to their pencil sharpeners. I know I would have done.. Zinc - 9-5-2007 at 10:35
I don't think that they are made of Mg anymore. The one I have is very old.
A little off topic but does anyone know in what ratio should Al and Zn be mixed to obtain a alloy that shrinks at least that can be obtained with
those two metals?
[Edited on 9-5-2007 by Zinc]12AX7 - 9-5-2007 at 16:16
Shrinks how much?
I don't have a graph of (or data on) shrinkage vs. alloy, but I would imagine it's roughly linear between the two metals.
TimZinc - 28-6-2007 at 04:02
Quote:
Originally posted by 12AX7
If you want to cut the amount of copper to make it cheaper or lower-melting, the best you can do is yellow brass circa 35% (on the verge of white
(beta) brass), melting point about 1600F (870C).
Tim
Can it be made by melting Al and adding solid Cu to it so the Cu dissolves? Will it dissolve? If yes how long would it take?
What is the lagest amount of Zn that can be added to Cu so that the alloy has a brass collor? What would be the melting point of that alloy? Can it be
made by dissolving Cu in molten Zn?12AX7 - 28-6-2007 at 13:49
What the devil does aluminum have to do with brass?
Around 35% Zn is the end of yellow brass and the beginning of beta (white) brass, with a melting point in the 1600F range. This can all be looked up
on an alloy database such as www.matweb.com.
Brass is made by adding zinc to copper. Hold the solid metal over the melted copper until it starts dripping, then firmly drop it into the melt and
stir vigorously. It will splatter. This procedure results in the least splatter. The worst thing you can do is let the zinc float on top of the
melt and sputter away. It needs to be stirred quickly. Use a slag cover to reduce evaporation.
As the melting point falls (towards the end of the addition, maybe >20% Zn), you will have to worry less about splatter.
TimZinc - 28-6-2007 at 13:57
Quote:
Originally posted by 12AX7
What the devil does aluminum have to do with brass?
Tim
I don't know. I just want to know if Cu dissolves in molten Al. Does it?
Quote:
Originally posted by 12AX7
Brass is made by adding zinc to copper. Hold the solid metal over the melted copper until it starts dripping, then firmly drop it into the melt and
stir vigorously. It will splatter. This procedure results in the least splatter. The worst thing you can do is let the zinc float on top of the
melt and sputter away. It needs to be stirred quickly. Use a slag cover to reduce evaporation.
Tim
So I can't add solid Cu to molten Zn and wait for it to dissolve?
[Edited on 28-6-2007 by Zinc]not_important - 28-6-2007 at 15:32
Zinc's boiling point is below the melting point of copper, you tend to lose a lot of zinc when you keep it very hot. It might work if the copper were
in small peices, to maximise the surface area. Brass was once made by reducing zinc ores along with copper ores, or in the presence of metallic
copper. The zinc would vapourise and diffuse into the copper, this method was used until the technology of producing metallic zinc was developed.
Yes, copper dissolves in aluminium. At one time aluminium bronze was made by electrolysing molten salts containing aluminium compounds, using copper
electrodes. The copper would dissolve in the aluminium being formed, resulting in a pool of the alloy at the bottom of the tank.
The solution of copper in aluminium is slow enough and has other problems. These days it seems to be common to melt copper and add some aluminium to
it to get a high copper alloy, which melts at a much lower temperature. That is added to molten aluminium to get the final alloy.
For many alloys the melting point is between the melting points of the two metals. At the lower end of the temperature range the higher melting point
metal may not be all that soluble in the alloy or other metal, to get a good mix you have to fully melt the mixture. These two effects mean that you
may have problems attempting to make alloys the way you want to.JohnWW - 28-6-2007 at 15:57
I think that this ebook, posted recently on todoquimica.net by Persseux, is pertinent to this thread:
Metals Handbook Desk Edition
Second Edition 1998 | ISBN: 0871706547 | Publisher: ASM International | English | Format: PDF OCR | 23 MB | 2571 Pages
The Metals Handbook Desk Edition is intended to serve as a comprehensive single-volume reference source on the properties, selection, processing,
testing, and characterization of metals and their alloys. Although the information presented in this Volume is drawn principally from the 20 volumes
of the ASM Handbook series, it should not be considered simply an abridged version of the larger work. Instead, the Metals Handbook Desk Edition draws
upon the complete arsenal of ASM products--both print and electronic--as well as other key sources of information originating from other publications,
company literature, technical societies, and government agencies.
Posted By: persseux | Date: 27 Jun 2007 08:1512AX7 - 28-6-2007 at 17:31
Copper metal dissolves poorly in aluminum and zinc primarily due to oxides interfering, and secondarily due to kinetics (it's relatively cold, isn't
it?). Therefore, a flux is needed. A lot easier to fuse the copper, add some aluminum or zinc (not both) to make your master alloy, then add that to
the finished product.
50%wt Al/Cu master alloy melts about the same temperature as aluminum, so is an excellent source. It is essentially the theta intermetallic. It is
quite brittle.
TimZinc - 4-7-2007 at 15:00
I have heared that copper should be melted under a cover of charcoal. So when I add zinc to it to make brass do I have to remove the charcoal or stir
in the zinc with the charcoal that would later seperate and be easily skimed before pouring?12AX7 - 4-7-2007 at 17:56
Charcoal is preponderously bouyant in molten copper. Think about it
TimZinc - 7-7-2007 at 16:05
When I make brass do I have to melt the copper under a charcoal cover before I add zinc or not?12AX7 - 7-7-2007 at 18:18
If it works better with charcoal, then it does.
I mean really, think about it (did I say that before?), you're adding zinc, which is reactive and a deoxidizer, which is the purpose of the charcoal.
So is it really needed? Obviously, you can if you want to.
Tim
Laves Intermetallics
ciscosdad - 25-7-2007 at 23:18
Hi Tim,
I found your info on the Intermetallic compounds most interesting, and I have assiduously downloaded all the phase diagrams on that website. It also
took me on a bit of a detour trying to find out more about the Laves intermetallic compounds.
While I now know more than I did, the question that first came to mind is as yet unanswered.
How many (if any) of these Laves Intermetallics are as brittle and crumbly as the MgAl (and presumably MgZn). Is there anything one could look for in
the phase diagrams to identify this sort of behaviour? Have you made any of the MgZn?
Pardon my ignorance. My knowledge of metallurgy is very scanty. I have made the MgAl compound but no others.
I have speculated on the idea of using any of these easily powdered compounds that include Al as a means of obtaining extremely fine powders of the
associated metal.
eg Dissolve the MgAl in alkali (plus possible some chromate) to leave the Mg as obsecenely fine particles. If successful I guess it may be too fine
and reactive.
I believe the Raney Nickel catalyst is made in similar fashion, but have not explored that at all.
Do you have anything to add?12AX7 - 26-7-2007 at 14:22
MgZn is most assuredly brittle. I have made it myself; in a pyrotechnic mixture it is slightly more reactive than zinc, and much easier to powder as
I don't have a ball mill. I might say it's even more brittle than MgAl, but the residual hardness of each may be due to different alloying impurities
in my stock.
I've heard of Laves used in the context of precipitates for hardening, which is probably suitable. Most intermetallics interrupt deformation of the
surrounding matrix, improving its strength, almost regardless of the material's strength (but not necessarily of its shape, as can be seen in gray
cast iron, which consists of soft alpha ferrite with sharp-edged graphite flakes; contrast to ductile or malleable irons, where spheroidized graphite
does not impact the tensile strength).
Raney nickel is made by dissolving aluminum from nickel, which occurs with acid or base; magnesium can't ever be exposed to solution, base or
otherwise, due to its high reduction potential (in excess of aluminum's, even). If you know of a solvent and complexing agent which will dissolve
aluminum, leaving magnesium, you might have a shot.
