 |
 |
 |
 |
 |
|---|---|---|---|---|
 |
 |
 |
 |
 |
Aluminium Page
I have put below a table of Aluminium specifications so that we know what we are working with, It is as accurate as the data I using which comes directly from Aluminium alloy data books.
It cross-references both U.K./ISO/&Imp; U.S.A. Aluminium alloy specifications along with there chemical compositions, freezing ( melting ) range, and patternmakers shrinkage's.
| Alloy | ISO | USA AA/ASTM | Cu | Mg | Si | Fe | Mn | Ni | ZN | Pb | Sn | Ti | Freezing point | Shrinkage allowance |
| LM0 | AL-99.5 | 150 | 0.03 | 0.03 | 0.3 | 0.04 | 0.03 | 0.03 | 0.07 | 0.03 | 0.03 | 0.0 | 657~643°C | 1.6% or 1/62 |
| LM2 | AL-Si10CuFe | 384 | 0.7~2.5 | 0.03 | 9.0~11.5 | 1.0 | 0.5 | 0.5 | 2.0 | 0.3 | 0.2 | 0.2 | 570~525°C | 1.3% or 1/75 |
| LM4 | AL-Si5Cu3 | 319 | 2.0~4.0 | 0.02 | 4.0~6.0 | 0.8 | 0.2~0.6 | .03 | 0.5 | 0.1 | 0.1 | 0.2 | 625~525°C | 1.3% or 1/75 |
| LM5 | AL-Mg5Si1 AL-Mg6 AL-Si12Fe | 514 | 0.1 | 3.0~6.0 | 0.3 | 0.6 | 0.3~6.0 | 0.1 | 0.1 | 0.05 | 0.05 | 0.2 | 642~580°C | 1.3% or 1/75 |
| LM6 | A413 | 0.1 | 0.1 | 10.0~13.0 | 0.06 | 0.5 | 0.1 | 0.1 | 0.1 | 0.05 | 0.2 | 575~565°C | 1.3% or 1/75 | |
| LM9 | AL-Si10Si2Mg | A360 | 0.2 | 0.2~0.6 | 10.0~13.0 | 0.06 | 0.3~0.7 | 0.1 | 0.1 | 0.1 | 0.05 | 0.2 | 575~550°C | 1.3% or 1/75 |
| LM12 | AL-Cu10SiMg | 222 | 9.0~11.0 | 0.2~0.4 | 2.5 | 1.0 | 0.6 | 0.5 | 0.8 | 0.1 | 0.1 | 0.2 | 625~525°C | 1.3% or 1/75 |
| LM13 | AL-Si12CuFe | 336 | 0.7~1.5 | 0.8~1.5 | 10.0~13.0 | 1.0 | 0.5 | 1.5 | 0.5 | 0.1 | 0.1 | 0.2 | 560~525°C | 1.3% or 1/75 |
| LM16 | AL-Si5Cu1Mg | 356 | 1.0~1.5 | 0.4~5.5 | 4.5~5.5 | 0.6 | 0.5 | 0.25 | 0.1 | 0.1 | 0.05 | 0.2 | 620~560°C | 1.3% or 1/75 |
| LM20 | AL-Si12CuFe | A 413 | 0.4 | 10.0~13.0 | 10.0~13.0 | 1.0 | 0.5 | 0.1 | 0.2 | 0.1 | 0.1 | 0.2 | 575~565°C | 1.3% or 1/75 |
| LM21 | AL-Si6Cu4 | 308 | 3.0~5.0 | 5.0~7.0 | 5.0~7.0 | 1.0 | 0.2~0.6 | 0.3 | 2.0 | 0.2 | 0.1 | 0.2 | 615~520°C | 1.3% or 1/75 |
| LM22 | AL-Si5Cu3 | 319 | 2.8~3.8 | 4.0~6.0 | 4.0~6.0 | 0.6 | 0.2~0.6 | 0.15 | 0.15 | 0.1 | 0.05 | 0.2 | 625~525°C | 1.3% or 1/75 |
| LM24 | AL-Si18Cu3Mg | A380 | 3.0~4.0 | 7.5~9.5 | 7.5~9.5 | 1.3 | 0.5 | 0.5 | 3.0 | 0.3 | 0.2 | 0.2 | 580~520°C | 1.3% or 1/75 |
| LM25 | AL-Si7Mg | A356 | 0.2 | 0.20~0.6 | 6.5~7.5 | 0.5 | 0.3 | 0.1 | 0.1 | 0.1 | 0.05 | 0.2 | 615~550°C | 1.3% or 1/75 |
| LM26 | AL-Si19Cu3Mg | 332 | 2.0~4.0 | 8.5~1.5 | 8.5~10.5 | 1.2 | 0.5 | 1.0 | 1.0 | 0.2 | 0.1 | 0.2 | 580~520°C | 1.3% or 1/75 |
| LM27 | AL_Si5Cu3 | U/K | 1.5~2.5 | 0.35 | 6.0~8.0 | 0.8 | 0.2~0.6 | 0.3 | 1.0 | 0.2 | 0.1 | 0.2 | 605~525°C | 1.3% or 1/75 |
| LM28 | AL-S19CuMgNi | U/K | 1.3~1.8 | 0.8~1.5 | 17~20 | 0.7 | 0.6 | 0.8~1.5 | 0.2 | 0.1 | 0.1 | 0.2 | 575~520°C | Tall Feeders are required to prevent shrinkage pipes extending into the casting. |
| LM29 | AL-Si23CuMgNi | U/K | 0.8~1.3 | 0.8~1.3 | 22.0~25.0 | 0.7 | 0.6 | 0.8~1.3 | 0.3 | 0.1 | 0.1 | 0.2 | 770~520°C | |
| LM30 | AL-Si17Cu4Mg | 390 | 4.0~5.0 | 0.4~0.7 | 16.0~18.0 | 1.1 | 0.3 | 0.1 | 0.2 | 0.1 | 0.1 | 0.2 | 650~505°C | |
| LM31 | AL-Zn5Mg | U/K | 0.1 | 0.25 | 0.5 | 0.5 | 0.1 | 0.1 | 4.8~5.7 | 0.05 | 0.05 | 0.25 | 615~570°C | 1.3% or 1/75 |
So now that we know what to use, where do we get some, well the best way is to buy some, or if your any thing like me then go to the local scrap yard and lets see what there is to hand.
If your lucky you might find some Aluminium wheel rims, these, especially from speedwell, have there Aluminium alloy specification cast on the inside of the wheel, most likely in the form ( ALSi7Mg or G-ALSi7Mg The German spec.). But given the fact that most scrap Aluminium will not have it's specification neatly attached, the next best way is to look at the following rule of thumb guide.
LM0; ( pure Aluminium) Electrical wire, food and chemical plant, typical pouring temperature of 740°C.
LM;2 Almost any form of die cast Aluminium as this is the most common alloy used, typical pouring temperature of 615~700°C.
LM4; cylinder heads, inlet manifolds crank cases etc. the only problem with this source is the oil contamination because the oil will cause hydrogen absorption into the melt and cause porosity, but has fairly good machining properties typical pouring temperature of 720°C.
LM5; marine applications, food plant, door furniture, car fittings, decorative uses, and chemical plant, this alloy has superior machining properties and will take a high polish typical pouring temperature of 700°C.
LM6; and LM9; both of these alloys have marine applications and have excellent fluidity which enable thin sections to be cast but is difficult to machine due to the high silicon content, typical pouring temperature of 725°C.
LM12; humm. according to the book, this alloy is most commonly used on hydraulic components, well if you fancy striping down this stuff.........and its properties aren't that good either a bit similar to LM6, typical pouring temperature of 710°C.
LM13; this is alloy is most commonly used on pistons has good fluidity, and is a general good casting alloy with reasonably good machining properties and is probably one of the best all round alloy's to use, typical pouring temperature of 710°C.
LM16; Air compressor pistons, Aircraft alloy, Fuel Pumps, and water cooled cylinder heads, This alloy has farley good machining properties and reasonable fluidity with a typical pouring temperature of 710°C
LM20; Domestic and office fittings &, street lighting, This alloy has excellent Fluidity and can be cast into thin and intricate castings, but has poor machinability typical pouring temperature of this alloy is not stated..
LM21; general engineering alloy, tool handles, gearboxes, electrical tools, this alloy good fluidity and good machinability, possibly better than LM4, typical pouring temperature of 720°C
LM22; Road transport vehicle cross-bearers, structural components good fluidity, the stated machinability is good with chill castings with a typical pouring temperature of 720°C but no mention of sand casting.
LM24; General die castings, we all know this metal the one that regularly welds it's self to the tools, but with good lubricant a reasonable cut can be expected, good fluidity and typical pouring temperature of 700°C
LM25; aircraft pumps, and fittings along with nuclear energy instillations( don't do it! your castings might have a nice friendly glow in the dark) good machinability if heat treated good fluidity ok for thin sections typical pouring temperature of 710°C
LM26; Pistons diesel and petrol engines this alloy has good machinability better than LM1, good fluidity with a typical pouring temperature of 700°C
LM27; my favourite, commonly found in car wheels Good machinability, good fluidity and a typical pouring temperature of 710°C.
LM28~31; are all to be found in high performance components like unlined die cast engines and due to there high silicon content are difficult to machine to a high finish, below average fluidity and pouring temperatures are not stated these alloys are tricky to work and like critically controlled conditions.
Aluminium Porosity its causes and how to avoid it.
The following section deals with Hydrogen absorption
Hydrogen has a low solubility in solid
Aluminium and a high solubility in liquid Aluminium (which increases with temperature).
There is, therefore, a large change in solubility at the melting point of the alloys.
93-96% of dissolved hydrogen comes out of solution from the liquid Aluminium on solidification and this excess hydrogen will form gas pockets in the solid metal.
The alloying elements, Silicon, Copper, Manganese & Zinc lower the hydrogen reduce hydrogen solubility, while Magnesium, Nickel, & Titanium increase hydrogen solubility.
Some hydrogen in molten metal comes from dissociation of water vapour from the atmosphere on contact with liquid Aluminium, Water vapour from burner fuels, from damp flux, from the crucible it's self, or refractory's, from oily scrap charges and from dirty foundry tools, these all provide sources of hydrogen that dissolve in the melt.
The simplest method to reduce hydrogen absorption is to leave the dross floating on the top of the melt until the last possible moment prior to pouring,
This layer of dross will form a barrier, which protects the melt from atmospheric contact.
All metal that is to be added to the melt should be thoroughly heated to the point at where it becomes brittle with heat, so that all water, paint and oil are burnt off. The gas flame should be run slightly "Oxidising" that is deep blue so as to reduce hydrogen in the combustion products.
And never over heat the melt as the hotter the melt temperature the more hydrogen will be absorbed, so it is important to only use just enough heat to melt the metal and avoid local heating (see stretching photo) there you can clearly see the bottom of the crucible is definitely hotter than the top!
You can of course use de-gassing tablets but these will give off fumes and are unlikely to be good for your health, alternately you could very, very, slowly bubble fine dry nitrogen bubbles through the melt to de-gas, I have not tried this as special ceramic nozzles are required.
Finally you could of course just keep the lid on!
Whist researching for this page I have noticed several sites advocating the use of steel crucibles, I would strongly advise against this for two reasons.
- When Aluminium is fully molten it is highly acidic and will attack the steel in which it is held, and ultimately dissolve the crucible and or the weld holding it together, and having the bottom drop out of the crucible when you are least expecting it is not good, as I have already dropped one pot of Aluminium I can defiantly say it is not the thing to do.
-
The products of this acidic attack (iron) heavily modify the Aluminium alloy with this effect " High iron contents decrease castability as sludge phases form with manganese and chromium etc, shock resistance is decreased as with ductility, machinability and corrosion resistance"
So having trooped around several scrap yards to gain the correct Aluminium alloy you then turn it into a useless chunk of sludge by melting it in a steel/iron pot, this does not sound good sense to me!
The cost of a clay graphite crucible is not great but is benefits are, and with careful use and cleaning it will out last any steel pot.
( so long as you don't drop it or let it get wet!!!)