6061: further thoughts and new information

[Throttle_monkey1]

For farmboy's example of smashing it against a rock yield strength isn't that important as it's a tensile property. For his example you need toughness and a balance of hardness and ductility.

But I agree 100% with what you're saying. The uppers and lowers just aren't that stressed and the difference between 7075 and 6061 are negligible when used as uppers and lowers.

 

[hori]

But for me, for now, I am no longer concerned about the use of 6061 in the NEA receiver. I have been warned by some people that it will be susceptible to pin hole elongation and I intend to spec mine out when I get it and measure it regularly for the duration of its service life in the hopes that I can provide useful data to people.

But this resolves my concerns.

I forwarded this thread to Colt and they are going to go back to 6061 after the new year. I mean what the hell were they thinking using 7075 all these years when 6061 will do just fine and even better by some
Merry xmas everyone

 

[Lee Enfield]

What you need to be looking at here is Yield Strength and Ductility. You would need a stress-strain curve for each alloy. Another way of putting it is by looking at the alloy's ability to absorb mechanical (kinetic) energy up to the point of failure.

A quick and dirty lab test would be to prepare two identically sized samples, anodize them using the NEA process, and then destructively test both samples using the chary method.

Let me save you the anticipation though... the difference between the two will be, for all practical intents and purposes, negligible.

Ummmnnn that's because annodizing is just a surface finish. In your example the important issue would have nothing to do with the anodizing, and everything to do with the heat treating.

Annodizing is strictly surface finish wear and corrosion resistance.

I bring this up because I believe that you know the difference, but some of the readers do not.

I would offer that the true test would be to heat treat each material to its particular optimum for the purpose and run a side by side destructive comparison.

Or simply reproduce the upper receiver deformation testing on the m4 c website, using a forged 7075T6 flattop against a billet 6061 nea flattop. That should answer my questions, rather than a bunch of regurgitated conjecture.

 

[Lee Enfield]

I'll even purchase 1 of the receivers if someone has the wherewithal to honestly record and report the outcomes.
PM me if your serious about it.

 

[gunny bunny]

Been reading quite a bit about this, and Young's modulus, in my understanding, in basic terms measures elasticity.

So if you took a fore end rail made from 6061 and one of 7075 and stuck each end on a block of wood, and stepped on the middle of each rail, you could use this.

Or if you grabbed each end of the rail and tried to stretch it, you could use this.

What Young's modulus doesn't measure, is if you took those same two rails and smacked them against a rock, which one would come out of it better.



A BCG travelling back and forth inside the upper, doesn't load it.

It's not the same as the load placed on an aircraft wing.

This is my understanding but like yourself, I'm not an engineer either.

Sounds like the important part of measuring whether or not the upper will contain a catastrophic failure, and that the 6061 will do as good of a job as the 7075 forging.

As far as smashing it against a rock, even the DD rails you carry are 6061, so if 6061 is a problem in standing up to external strikes and daily wear and tear most of the rail manufacturers in the world need to quickly find a replacement material.