Aluminum numbering for dummies

[derekg]

Hi All,

I need to order some hex stock and am confronted with a choice of 2011 or 6061 aluminum. As I do not know what the numbering system means (I just use whatever is in my scrap bin), I looked it up on Wikipedia (http://en.wikipedia.org/wiki/Aluminium_alloy) and now I am completely confused. Is there a very simple "rule of thumb" chart or guide to aluminum numbering? I realize nothing is going to be as simple as "good" or "bad", but am hoping I can be directed somewhere that will help me understand why the major alloying element or whether wrought or cast or aerospace vs marine vs automotive matters. I'm not looking to become a metalurgist, but just want to understand the basics so I can make an informed choice.

BTW, the project at hand just requires simple threading and turning on the lathe for an automotive water fitting, so I am sure "whatever is cheapest" would work in this case, but I still would like to gain some knowledge.

Thanks, Derek G

[winchman]

This looks pretty good, and I think it's easier to understand:
http://www.azom.com/details.asp?ArticleID=310

Roger

[mechanicalmagic]

McMaster-Carr

Not a rule of thumb, more like my mouse finger.
I click McMaster, then type Aluminum in the search bar,
then click "About Aluminum"
then read the page.
All sorts of good info, weldability, machining properties, hardness, strength etc.

http://www.mcmaster.com/#about-aluminum/=54ak5e

[Boucher]

Aluminum Alloys for the machine shop.

I bought a bunch of 7075-T6 bushings from a surplus place years ago. It will spoil you. It is my first choice The majority of what I buy is 6061-T? I can't weld AL so that is not important for me.

[Black_Moons]

nifty.. looks like that 2011 stuff might be better to machine but won't weld(easily and/or with a strong bond. Experiance has taught me you can weld just about anything given the right setup, or if you are willing to do with a very weak bond)

6061 machines easily enough however. Mirror finishs half the time on my lathe without trying.

[gnm109]

6061-T6 is very common and is my first choice when making something structural. It welds nicely and machines very cleanly.

A friend who has a professional shop will call me and give me his cutoffs and remnants. Most of it is 2XXX grade and 6XXX. I got some 5XXX angle fiom him a while back and used it to make a bracket to hold my DRO. It is terribly gummy when attempting to machine it. It welds OK but you have to stop now and then and chisel the gummy remnants off of your end mill if you try to machine it.

So 6061 is my favorite if I have a choise.

[Evan]

2000, 6000 and 7000 series are all heat treatable aluminum. 1000 series is pure aluminum, aka electrical grade and soft as butter.

The rest, 3000, 4000 and 5000 are all work hardening only and are all weldable. They machine ok but if they are welded they go to a soft condition and do not regain strength unless peened or otherwise worked.

The heat treatable grades have either copper or zinc as the main alloying ingredient with a small amount of silicon. The 6000 series is easily weldable and if left to sit for a few day will regain much of it's original strength by what is called ageing. 2000 has too much copper to weld well. It can be spot welded and some alloys may be tigged and it can be friction stir welded. It machines beautifully and is nothing like the aluminum your grandma used to make. It's strong as heck and so cannot be bent to a sharp radius without cracking. The most common alloy is 2024 in various tempers, usually T-3, T-4 or T-6.

The 7000 series is even stronger than the 2000 series and every thing I said about 2000 applies to 7000 series except it is even less weldable. The main alloying ingredient is zinc. It can only be bent with a very large radius if it is in a full strength temper such as T-651. It's the stuff they make aluminum keys with. The most common alloy is 7075 in a T-651 temper. It's about 20% harder than mild steel and about the same strength at 1/3 the weight. It's the only grade that makes swarf needles that stick you like steel will. It machines beautifully but has a nasty tendency to grab drill bits. Never try to open a hole in 7075 by just a little bit.

In general the stronger the aluminum alloy the more prone it is to fatigue cracking. The closer it is cycled to it's maximum elastic limit the faster it fatigues. 7075 if taken close to the limit may fail in just a few hundred cycles. When it fails it will suddenly break with a snap and no plastic deformation.

There are many other grades and type with specific applications such as the 8000 series developed expressly for aircraft skins and the entire range of high silicon grades for casting. Some grades are close to aluminum bronze with high amounts of copper and are used in high heat applications such as pistons.

[Black_Moons]

Very cool and detailed discription evan. that combined with mcmasters charts says a whole lot.

Intresting at alloys that can be spot welded but not easily welded by other methods. And intresting that 3/4/5000 series can be welded but goes soft. Those 'weldability' charts often seem to leave out *why* its not recommended to weld. (Ie, porosity, weakening of parent metal, outright horrable bonding, etc)
Sometimes things are designed not for strength but rigidity, where a weld thats weak is fine as the parent metal is dozens of times stronger then whats required.

[lazlo]

And intresting that 3/4/5000 series can be welded but goes soft.

6061 is easily weldable, but loses most of it's strength in the process. Or more accurately, when you weld 6061 you lose (anneal) the heat treatment in the HAZ.

If you let it age harden, it eventually regains a little strength back -- the Alcoa Structural Handbook states says "the expected minimum yield strength of material adjacent to the weld in 6061-T6, in the direction parallel to the weld, is about 11ksi."

6061-T6 is 35ksi yield.

A great reference for welding aluminum, that we were given in the ACC welding classes:

Common Mistakes Made in the Design of Aluminum Weldments

[Pherdie]

I find this as helpful......

http://www.speedymetals.com/informat...erialframe.htm

[Evan]

Robert,

6061 will regain about half of it's strength in a week or so IF it started from a T-6 condition. The loss of strength is dependent on the distance from the actual weld as can be seen in this chart:



You can also increase the strength after welding by artificial ageing. If it is placed in an oven at about 350 degrees F for 6 to 8 hours it will come back about 80% of the way to a T-6 condition.

[mechanicalmagic]

You can also increase the strength after welding by artificial ageing. If it is placed in an oven at about 350 degrees F for 6 to 8 hours it will come back about 80% of the way to a T-6 condition.

This is the process used by sheet metal benders for re-hardening 6061 that has been softened to enable bending.

I use an Acetylene only flame to apply soot to the sheet metal. Then I adjust to a neutral flame and slowly heat the bend area, at the temperature where the soot combines with Oxygen, and leaves the surface clean, it is annealed. Bend material, then artificially age the metal to regain most of the original strength.

[lazlo]

6061 will regain about half of it's strength in a week or so IF it started from a T-6 condition.

That sounds about right, and agrees with the Alcoa handbook: you lose 2/3rd of 6061's strength by welding it (35 versus 11 Kpsi).

You can also increase the strength after welding by artificial ageing. If it is placed in an oven at about 350 degrees F for 6 to 8 hours it will come back about 80% of the way to a T-6 condition.

That's very optimistic. According to the AWS Welding Handbook, to bring 6061-T6 back to even T4 strength (14ksi for extruded tube and 16ksi for drawn tube) requires full solution heat treatment in an environmentally controlled furnace: 970° F for 10 minutes per inch of thickness and a rapid quench.

Point being, once you weld 6061, you've pretty much ruined it. That's the reason there's no such thing as 6061 filler wire, and why you can't weld 6061 autogenously (it cracks -- try it ).

By the way, that's also why aluminum bicycle frames are made from 7005, which gains it strength from the alloy, and not heat treat. So you can weld 7005 all you want, and it doesn't adversely affect the tensile strength.

[tigmusky]

great thread!!!

Daye thanks

[Evan]

By the way, that's also why aluminum bicycle frames are made from 7005, which gains it strength from the alloy, and not heat treat. So you can weld 7005 all you want, and it doesn't adversely affect the tensile strength.

Where did you ever get that idea from? The condition of 7005 T-6 after welding is about the same as all other heat treated alloys of aluminum when welded, with maximum yield strength of only 11 KSI or so. At full T-6 temper it is 42 to 50 KSI, quite a difference. After welding it regains strength by the same ageing process as 6061 or other heat treatable alloys. T-6 means heat treated. In the case of the 7000 series alloys they can be substantially returned to their previous strength quickly by artificial ageing or slowly by natural ageing. They may also be "over aged" which reduces strength slightly but reduces the cracking tendency a lot.

Heat Treating T Temper Codes
T1 - Cooled from an elevated temperature shaping process and naturally aged to a substantially stable condition.
T2 - Cooled from an elevated temperature shaping process, cold worked, and naturally aged to a substantially stable condition.
T3 - Solution heat treated, cold worked, and naturally aged to a substantially stable condition.
T4 - Solution heat treated, and naturally aged to a substantially stable condition.
T5 - Cooled from an elevated temperature shaping process then artificially aged.
T6 - Solution heat treated then artificially aged.
T7 - Solution heat treated then and overaged/stabilized.
T8 - Solution heat treated, cold worked, then artificially aged.
T9 - Solution heat treated, artificially aged, then cold worked.
T10 - Cooled from an elevated temperature shaping process, cold worked, then artificially aged.