Aluminium numbers. What do they mean?
Comments
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Different aluminum alloys and treatments are designated by a numerical code.
They indicate what other stuff is mixed in with the aluminum. Pure aluminum isn't all that strong. Add some silcon, magneisum, zinc, copper, and other things, and the result will be far stronger.
The first digit tells what "family" it belongs to:
1xxx Commercial aluminium (more than 99 per cent Al)
2xxx Copper
3xxx Manganese
4xxx Silicon
5xxx Magnesium
6xxx Magnesiun and silicon
7xxx Zinc
8xxx Other elements
The other 3 digits can be looked up in a table, to tell you how much of each they get, and how good the result is. They are assigned in order requested, they don't have any relationship to how much of each ingredient is used, or the properties of the result. (unlike steel alloys, whose numbers (1020, 4130, 4340) include the carbon content.)
If you see things like -T6, following the alloy series, those describe any heat treating the stuff got after it was made. Getting this done correctly, is critical to the strength of the frame. For most aluminum frames, it is done after the frame is welded, as the heat from the welder will change the metal (usually makes aluminum alloys softer) Heat treating typically involves heating to near melting (900-1000F, it melts around 1100F, your oven self cleans at 800-850), holding it there for some amount of time (for thin tube, 1/2-2 hours or so) cooling suddenly (dunk in water), then a long bake (8 or more hours) at a lower temprature (like 350F).
The different alloys vary in tensile strength, corrosion resistance, welding compatibility, ductility, and machineability. The density of aluminum alloys don't vary much at all (under 5%) and the stiffness, doesn't change.
Each alloy has good points, and bad points. What counts as good, and what is bad depends on what you are going to do with it. Some very strong alloys can't be welded, so they make bad frames, and great chainrings. Another might give up some absolute strength, but gain some resistance to cracking. One may cost more, but the heat treating process is cheaper. If you are bolting or bonding things together, you can mix alloys. If you are going to weld, all the welded parts have to use identical filler material, and heat treating schedule. (so you can't mix 6061, and 7005 in the same welded structure)
It's the designers job to chose correctly amoung the various tradeoffs. If the desinger chose well, even a not particularly exotic material can do the job just fine. Pick wrong, and even exotic super-alloys will break.
Double-Butted:
Not a strange anatomical problem, but a method of making bikes lighter. The tubes are thick at the joints for strength, but get thinner in the middle for weight saving, because the stress on the centre section of the tube is lower than that at the ends where it is welded. This is a sign of quality0 -
"Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
Parktools :?:SheldonBrown0 -
how do you double butt a tube? Is it something that can be done in your average metalworking workshop, or do you need specialist drawing.cold-forming equipment?0
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ride_whenever wrote:how do you double butt a tube?
I'd imagine it's done by variable die "size/wall thickness" during extrusion of the tube. I don't think aluminium extrusion would be done too easily at home.0 -
there are many ways.
cutting. hydro forming, drawing at differing speeds....
External butting is easier."Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
Parktools :?:SheldonBrown0 -
As far as I knew, the extrusion process doesn't allow for changes in cross section...
Butted tubing is made by drawing over a mandrel.
It's explained very well in terms of bicycle tubing here:
http://www.desperadocycles.com/The_Lowd ... _page2.htm0 -
apreading wrote:Different aluminum alloys and treatments are designated by a numerical code.
They indicate what other stuff is mixed in with the aluminum. Pure aluminum isn't all that strong. Add some silcon, magneisum, zinc, copper, and other things, and the result will be far stronger.
The first digit tells what "family" it belongs to:
1xxx Commercial aluminium (more than 99 per cent Al)
2xxx Copper
3xxx Manganese
4xxx Silicon
5xxx Magnesium
6xxx Magnesiun and silicon
7xxx Zinc
8xxx Other elements
The other 3 digits can be looked up in a table, to tell you how much of each they get, and how good the result is. They are assigned in order requested, they don't have any relationship to how much of each ingredient is used, or the properties of the result. (unlike steel alloys, whose numbers (1020, 4130, 4340) include the carbon content.)
If you see things like -T6, following the alloy series, those describe any heat treating the stuff got after it was made. Getting this done correctly, is critical to the strength of the frame. For most aluminum frames, it is done after the frame is welded, as the heat from the welder will change the metal (usually makes aluminum alloys softer) Heat treating typically involves heating to near melting (900-1000F, it melts around 1100F, your oven self cleans at 800-850), holding it there for some amount of time (for thin tube, 1/2-2 hours or so) cooling suddenly (dunk in water), then a long bake (8 or more hours) at a lower temprature (like 350F).
The different alloys vary in tensile strength, corrosion resistance, welding compatibility, ductility, and machineability. The density of aluminum alloys don't vary much at all (under 5%) and the stiffness, doesn't change.
Each alloy has good points, and bad points. What counts as good, and what is bad depends on what you are going to do with it. Some very strong alloys can't be welded, so they make bad frames, and great chainrings. Another might give up some absolute strength, but gain some resistance to cracking. One may cost more, but the heat treating process is cheaper. If you are bolting or bonding things together, you can mix alloys. If you are going to weld, all the welded parts have to use identical filler material, and heat treating schedule. (so you can't mix 6061, and 7005 in the same welded structure)
It's the designers job to chose correctly amoung the various tradeoffs. If the desinger chose well, even a not particularly exotic material can do the job just fine. Pick wrong, and even exotic super-alloys will break.
Double-Butted:
Not a strange anatomical problem, but a method of making bikes lighter. The tubes are thick at the joints for strength, but get thinner in the middle for weight saving, because the stress on the centre section of the tube is lower than that at the ends where it is welded. This is a sign of quality
Great explanation! But where does Scandium come in the equation?0 -
Yes it was a very good explanation. I read through all posts about Materials Science and normally find something which indicates to me that they don't know what they're on about... I didn't think that aluminium was water quenched though. :?
Scandium is simply another alloying element they can use. They add ~0.5%.
http://www.scandium.org/Sc-Al.html0 -
synchronicity wrote:As far as I knew, the extrusion process doesn't allow for changes in cross section..
I guess that's why I screwed up my polymer processing module. I'm more of a ceramics guy
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