Thread: Identifying Aluminium

Aluminium is mostly graded on it's hardness. Could you find someone who has access to a harness tester? Or go to an aluminium distributor and ask them? Otherwise I don't think you can identify aluminium by it's look. I could be wrong though

If you're trying to determine certain alloys then I think I remember from one of my textbooks that the various alloying elements will react with certain types of acid and turn an exposed surface black or some such. I reckon the copper bearing alloys were the ones they mentioned in particular. Hardness could be a bit ambiguous as the heat treatments also vary a great deal. I've played with 2024 and some 6xxx series for things that I don't think I could tell apart in any way at all. Hardness, machinability or otherwise. Although 1xxx series will usually be very malleable and oxidise very quickly to a dull finish! Certainly an interesting quest. Good luck!

For casting purposes, you'd be better off sticking to collecting aluminium from existing castings, such as lawnmower bodies or mag wheels.

Originally Posted by Master Splinter

For casting purposes, you'd be better off sticking to collecting aluminium from existing castings, such as lawnmower bodies or mag wheels.

Thanks for all the replies guy's.

It is mostly castings I am talking about.

Eg. Car carburettors and fuel pumps are I believe cast from zinc.

I dismantled an old sat dish and found castings which were much too heavy for ali.

The one that decided me to post this question was a heat sink from a car stereo which was quite large but I was unsure as to the weigh versus volumn. It had a section across the full width about 15mm square.

It would be easiest to stick to "known" castings if I knew which ones to use. I mentioned mag wheel use to the boss where I get my tyres fitted and he said they were magnesium. Not sure about this one.

Dean

Mag wheels havent been magnesium for decades. They stopped that once they realised that overheated brakes could ignite the rims. After that you have the world's brightest car for a few minutes. Also, magnesium is both more expensive and and less resistant to corrosion. If you have a real old rim you want to check, strike it with a knife. In theory, magnesium should spark like a flint.

I can't say I've heard of carbys being cast from zinc, but auto ones may differ. All the one's I work with (aero jobbies) are aluminium for the vast majority.

Originally Posted by Durdge39

Mag wheels havent been magnesium for decades. They stopped that once they realised that overheated brakes could ignite the rims. After that you have the world's brightest car for a few minutes. Also, magnesium is both more expensive and and less resistant to corrosion. If you have a real old rim you want to check, strike it with a knife. In theory, magnesium should spark like a flint.

I can't say I've heard of carbys being cast from zinc, but auto ones may differ. All the one's I work with (aero jobbies) are aluminium for the vast majority.

Interesting about the mag in mags. I remember seeing a news article years ago about a racing car belonging to Allan Moffat being stolen and found burnt out. The article mentioned the expensive magnesium rims that were fitted. I think the finding of it burnt out was a second article later. It showed a picture of the car sitting on its expensive but still intact magnesium (alleged) rims.

Some car castings have a slight yellow cast to them. I had heard they were zinc. The problem is how to tell the difference. Put a heap of them together and you get a huge range of appearances caused by numerous factors.

Dean

If they were zinc then they might melt at an appreciably lower temperature - Wiki says zinc will melt some 200 degrees lower than aluminium. Might be worth a shot?

Originally Posted by Durdge39

If they were zinc then they might melt at an appreciably lower temperature - Wiki says zinc will melt some 200 degrees lower than aluminium. Might be worth a shot?

Thanks for that tip. I did not even think of melt temp as ali has a relatively low melting point. Worth checking out.

Dean

Lots of old carbies are a high zinc content alloy. A rough way to figure it out is if it has really small detail (part numbers or whatever) cast in, and it feels heavier than it should, then it's one of the various zinc based pot metals.

I've heard that a drop of hydrocholric acid on zinc will fizz rapidly and go yellow, while it will just bubble slowly and stay clear on aluminum, but I've never tested this.

die cast " carbie parts " would be zink with any thing from 8% too 25% aluminum
die cast is easy to see , the marks from the die , look the same as plastic die marks , cast aluminum wont have die marks

the die cast Zamak25 ( 75% zinc 25% aluminum ) is worth keeping , mixed 89%copper and 11% zamak25 will make a nice " false gold " brass

Originally Posted by Master Splinter

Lots of old carbies are a high zinc content alloy. A rough way to figure it out is if it has really small detail (part numbers or whatever) cast in, and it feels heavier than it should, then it's one of the various zinc based pot metals.

I've heard that a drop of hydrocholric acid on zinc will fizz rapidly and go yellow, while it will just bubble slowly and stay clear on aluminum, but I've never tested this.

What you would have created here is soldering fluid. Another thing I did not think of until reminded. What is happenning to my brain? Don't answer.

Dean

It is becoming much clearer now. I took some pictures of an old stationary motor carby of unknown source but they did not show the colour as required. Now it seems I don't need the pics. Thanks for your help SawDustSniffer and Master Splinter, I do know what you mean by the casting marks.

I cut a small piece from the carby and tried to melt it with my mini butane torch. Melted very quickly. Ali did not melt at all.

I have started collecting the zinc bits now. What sort of things could zinc be used for. It is going to be easy to melt it.

Dean

pure zinc shrinks a lot
7000 series alloys are zinc based , i was making some end caps for a home made Air Ram and added 8%zinc and 4% copper to extruded ( 99.9%) aluminum , dam its hard , and machines well , nice ring to it when struck as well

the difference between copper and brass is only the zinc added , bronze is Tin

with straight zinc , you have to watch the shrinkage , shrink bobs nice and close to thick parts to feed in extra metal as it cools , the surface finish is way better than aluminum , and it will flow into thinner areas easier , its good stuff , machines better than most aluminiums

its a lot heaver than aluminum , but what do you make thats weight critical ? , its a dull grey , 90% of people would not know , and even more would not care what its made of , zinc is good

Extruded aluminum is pretty well pure 98% at the worst , but they will add Magnesium ( less than 1 % ) , less than 1% silicon ,or Manganese , a lot of it is 1000 series , i called "carpil " the makers of the scrap i get ( window manufacture off cuts ) and they said they use 3050 aluminum , so its a good start to know what alloy it is , the trace elements 1%manganese , 0.5%silicon , 0.2% magnesium , are common to most alloys
Pure aluminum dose not cast well , its thick and gluggy and freezes quick , aluminum from cast parts of unknown alloy would be better than pure aluminium , as the manufacture knows what he's doing and byes ingots of selected alloy that cast well , engine heads would be the best machinable , bell housing aluminum proberly wont machine up as well , but would have better structural stiffness , lawn mowers ? the last one i sledge hammered apart i put in my Zamak ( zinc / aluminum ) pile , was not impressed ( guess that it was zinc , but it was definitely not majority aluminum )

Watch out for Magnesium , its all fun and games until , you destroy your crucible , furnace , and burn a hole to china , even worse would be if some one seeing the magnesium fire decides to squirt water on it , if you ever get one , just agree . your crucible / furnace wont survive , and watch it burn , dont move it , squirt it with water , oh and make shore you start your furnace in an area where a problem like that wont matter

scratch up a suspect peace with a screw driver , and put vinegar on it , if it foams , dont put it in your furnace , trace magnesium in low % is fine
i once noticed a lighter coloured heat sink in the " about too melt " pile , it just looked sus , and it misses out being fried , later i vinegar tested it and it was magnesium ,

dont forget

click on the banner to see some students get splattered in molten aluminum ( utube )


and a bit of good reading

click on the banner

degassing of your aluminum is a different topic , but when you melt aluminium it absorbs hydrogen , and the hydrogen forms bubbles as the aluminium cools , bubbling argon through it works , but i use "Pool Shock " chlorine , wrapped in al foil , ( make sure its dry, leave near the exaust hole to heat above 120c ) , and plunged to the bottom of the crucible in a graphite tube , you have about 7 seconds to run , the chlorine bonds with the hydrogen and come to the surface where it pops in a blue flame , spitting molten aluminium at you , after 30 seconds it calms down , and just chlorine powder comes to the top( no blue flames , still pops ) , if it keeps popping all the way through , a second " pool shock " wrap is needed , i use 4 tablespoons of chlorine to a full A10 crucible of aluminum

I have a heat sink, as mentioned previously that I am not sure about! I will test it and any other suspect bits with vinegar.

Dean