A stronger alternative to 7075-t6? 3

[SorryOciffer]

Looking to make some parts (nuts, about 1.5" diameter with a 1.25" bore) that will be torqued to about 30 ftlbs several times. Is 7075 adequate or is a stronger alloy available?
Thanks.

 

[Maui]

Why are you using aluminum? Why not steel?

 

[winstonsk]

Maybe 2099 or 2199? Those are fairly new alloys from Alcoa.

Sorry--my memory didn't seem to serve me well. These alloys are tougher than 7075, not stronger (at least according to a quick search).
That might be pertinent to your design goals, but I don't think there's enough information here to properly advise you.

 

[CoryPad]

It is not possible to answer your question about suitability of 7075-T6 or any other alloy for your specific application based on the information provided.

If you need another aluminium alloy that is stronger than 7075-T6, then try:

2090-T8X
7001-T6
7034-T6
7055-T7X
7068-T6
7150-T7X
7178-T6

 

[SorryOciffer]

Use will be for a barrel nut for a savage scout rifle and an ar15. The AR nut has a series of teeth around it that a barrel wrench engages and deformation from repeated installs or removals is a concern. Reason, to save weight. This is just a pet project. Material sciences interest me but are not my strong point.

Thanks guys...

 

[gruntguru]

Sounds like a minimal torque for a 1.25" thread. I have seen 1.5" wheel-nuts in 7075-T6 that are repeatedly torqued to over 150 ft lbs with no issues.

A typical torque for 1.25" steel bolts is over 1000 ft lbs. 7075-T6 has about 1/2 the tensile strength so shall we say 500 ft lbs?

je suis charlie

 

[SorryOciffer]

It's not much the overall tq I was concerned with, but the teeth the tq is delivered too. If you Google image search "ar15 barrel nut", you will see the "teeth" the wrench engages. If people belive 7075 is adequate, I'll run with it as 7075 is among the most common aluminum in the firearms industry...

Thanks!

 

[tbuelna]

The barrel nut of a standard AR15 is not that highly loaded. It is normally made from alloy steel because it has a very thin wall section at the relief undercut for the internal threads. If you simply change the barrel nut material from alloy steel to 7075-T6 aluminum, you might experience stress/fatigue problems at the thin wall section around the undercut. The alloy steel barrel nut does not weigh much. Are you sure the tiny amount of weight reduction from the aluminum barrel nut is worth the trouble?

 

[imcjoek]

It's not much the overall tq I was concerned with, but the teeth the tq is delivered too.

Hardcoat anodize? You need more wear-resistance/surface hardness and/or slap the operator. Yield strength is not going to help you.

 

[tbuelna]

Hardcoat anodize?....

The external threads on the upper receiver the barrel nut mates with are coated with PTFE-impregnated hard anodize.

 

[ornerynorsk]

My concerns would be aluminum-on-aluminum galling and over-torquing if you need to go another half a notch to get the gas tube lined up. I don't think it's worth the couple of grams weight saved.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[Maui]

I'd simply use a low grade off-the-shelf steel that's easy to machine and thread.

Maui

 

[ornerynorsk]

V7 makes a titanium Grade 5 barrel nut that weighs 22 grams, for only $67.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[WKTaylor]

SorryOciffer

There are several light-weight aerospace grade Titanium, Steel and CRES nuts that might work fine... off-the shelf... with SFL coatings. However, most are self-locking and could damage softer male threads.

There are specialty aluminum nuts for aerospace, however they require careful torque-control and a usually dab of lubricant such as cetyl-alcohol, oil or other lube such as SFL, to minimize thread-on damage... especially for multiple re-use. And YES installation torques must be carefully controlled/monitored... not eyeballed/WAG'd.

CAUTION. Multiple removal and reinstallation cycles often result in nut or bolt thread damage/wear that erodes thread quality... especially with aluminum parts.

NOTE
Steel/CRES/HRA/Titanium alloy parts can be made lighter while maintaining reasonable strength durability using tricks of the trade. The losses in strength and durability are relative to the location and amount of material removed and remaining surface quality [rough, sanded, polished, etc].

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true.
o For those who believe, no proof is required; for those who cannot believe, no proof is possible.
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion"]
o Learn the rules like a pro, so you can break them like an artist. [Picasso]

 

[gruntguru]

The torque values mentioned by the OP are a fraction of allowable values. Plus or minus 50% isn't going to do any damage.

je suis charlie

 

[WKTaylor]

BTW...

7XXX series aluminum alloys, heat treated/aged to -T6xxx are highly susceptible to Stress Corrosion Cracking [SCC] and Exfoliation Corrosion [EXCO]... really bad/unpredictable failure modes. These alloys should always be HT/Aged to -T7xxx temper(s) which grossly reduces SCC & EXCO susceptibility.

NOTE, for grins: Hi-Lok aluminum collars, intended for shear applications, would work well here... 'cept they always have to be replaced since the hex-drive element is [almost always] sheared off during installation.

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true.
o For those who believe, no proof is required; for those who cannot believe, no proof is possible.
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion"]
o Learn the rules like a pro, so you can break them like an artist. [Picasso]

 

[IRstuff]

These guys make theirs out of 7075-T6

http://aeroprecisionusa.com/ar15-bar-barrel-nut.html

http://www.jlbillet.com/308-7075-t6-barrel-nut-dpms-profile/

http://2a-arms.com/products/aluminum-barrel-nut

TTFN
I can do absolutely anything. I'm an expert!
homework forum: //

http://www.engineering.com/AskForum/aff/32.aspx

faq731-376 forum1529

 

[SorryOciffer]

Sounds like 7075 with a good assembly lube will work fine. Thanks for the info/suggestions guys.

 

[tbuelna]

wktaylor-

The material specified for the M4A1 upper receiver forging is 7075-T6 IAW QQ-A-367. After machining, the upper receiver is shot peened all over including the barrel nut threads. And then it is hard anodized IAW MIL-A-8625, type III, cl. 2. Seems to have performed OK over the past 2+ decades for hundreds of thousands of US military M4 carbines.

 

[ornerynorsk]

Yeah, there's not much force in play on an upper receiver as the bolt locks into the rear barrel recess. If you ever have one fire out-of-battery, which is not likely but it has happened, they fail spectacularly.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.