boring question:6061 vs 2011 al 2

[mrPelagic]

Hi There! I am interested in pragmatic details between Aluminum alloy properties as related to an application that I have.

2011-T3 vs 6061-T6 for application of a machined part (involving screw threads) in production. It is used for positioning, so *loads and speed are very low*. we need about 200,000 cycles.

Our legacy is to use a part that is 2011-T3, with type II class 1 clear anodize (we do not specify thickness of plating), nickel acetate seal.
We are contemplating switching to 6061 for cost reasons.

In another life, I worked extensively with 6061, having a "hard" anodize (.002 thick) & a teflon seal. Let me tell you, the screw threads were terrible, squeal-ey, and parts liked to gall together, giving off a puff of smoke when it happened.

So my questions:
why would one choose 2011 to start with? (I can't find any records, it was 20+ years ago)
Do you think 6061, being softer, may have a risk of higher wear?
Is the hard-anodize the reason that my threads were so screechy, or is that due to the softness of the Al?

other thoughts welcome!
thanks

 

[berkshire]

Your question is " why would one choose 2011 to start with? (I can't find any records, it was 20+ years ago)
Do you think 6061, being softer, may have a risk of higher wear?
Is the hard-anodize the reason that my threads were so screechy, or is that due to the softness of the Al?"
So from a 20 year old Alcoa book I can give you the following information ... 2011-T3 ultimate , 55000psi , yield 43000PSI, ( There is a note in the book saying that sections larger than 1.5inches will have a lower strength than this.), 6061-T6 42000 ultimate , yield 40000PSI . 2011 is chosen because it is one of the easiest alloys to machine, 6061 while lower cost, is a little stickier to machine, and will load up on tools unless lots of coolant is used.
This also may be why your anodized threads screeched when you put the screws in, the more resilient material may have left you with a slightly tighter hole.
I am attaching a link to an article on machining Aluminum which may or may not cover your next questions See page 764,
B.E.

You are judged not by what you know, but by what you can do.

 

[tbuelna]

To achieve 2x10^5 operating cycles with aluminum screw threads probably requires some type of hard surface coating. Something like electroless nickel with PTFE would seem like a better option than hard anodize. You just need to carefully adjust the machined part dimensions to allow for the plating thickness.

 

[btrueblood]

Why not use a threaded insert (Keensert, heli-coil, etc.)?

 

[mrPelagic]

thanks berkshire. sounds like it's cheaper to machine 6061 in china than 2011 here.
tbuelna, i agree. surprisingly, we have had great success with just typeII anodizing for many years. I would never have gone there, but speeds and loads are low, and it appears to work.
btrueblood, this is a legacy part- I am just giving a second opinion on the change. it will require some cycle testing... I am lucky that I get to design the new stuff, and going forward, I am hoping to use a different positioning technique.

 

[berkshire]

mrPelagic (Mechanical)
I am surprised that you find it cheaper to machine 6061 in China, since 2011 is known as free machining aluminum ,I would have thought it would be cheaper to get that machined there also.
B.E.


You are judged not by what you know, but by what you can do.

 

[WKTaylor]

1. Per the Aluminum Association Aluminum Design Manual [ADM-2010]...

TABLE 1 - COMPARATIVE CHARACTERISTICS AND APPLICATIONS...

2011 has a Machinability rating of 'A' for all '-Txx' tempers.. and lists 'Screw Machine Products' under 'typical application'...

whereas...

6061-T4 has a Machinability rating of 'C' for all '-Txx' tempers.. and lists 'Heavy-duty structures requiring good corrosion resistance, truck and marine, railroad
cars, furniture, pipelines' under 'typical application'...

Also... I'm mostly sure about this... 'hard anodize' on 6061 has lower hardness/quality/density than for most 2xxx series aluminums... hence poorer performance.

NOTE. A bake-on solid film lubricant [MoS2 based] such as MIL-PRF-46010 on the threads would help a lot!

2. FYI for comparison... typical Aerospace threaded parts made from aluminum alloys...

AN3-thru-AN20 [NASM3-20] DD bolts are made from 2024, forged and HT to -T6 [now -T81]. Threads are roll-formed. Finish is anodized per MIL-A-8625 Type I or II [sealed, may be colored for ID].

Fluid fittings were typically made from bar [simple axial shapes] or forgings [complex shapes] from 2024 HT to -T6 ['D' coded]. HOWEVER, Fittings made from 'D' code material are now [generally] 'not for new design' and have been superseded by 7075 HT to -T73 ['W' coded]. Threads are generally 'cut' to a high quality standard. Finish for 'D' code parts = ANODIZE PER AMS2472 OR MIL-A-8625, TYPE II, CLASS 2, DYE BLUE, DUPLEX SEAL PER PROCUREMENT SPECIFICATION. Finish for 'W' code parts = ANODIZE PER AMS2472 OR MIL-A-8625, TYPE II, CLASS 2, DYE BROWN, DUPLEX SEAL PER PROCUREMENT SPECIFICATION..



Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[mrPelagic]

ok, good. so I am not crazy. thanks again. I used to use tons of 6061-T6 in my marine engineering days.

this decision is being made by procurement. I have heard that the particular shop in China has trouble sourcing 2011?? this whole thing does not give me a warm fuzzy- too many illogical decisions. but I have more important projects on my list...

time to decide if this is a battle worth fighting.