Alloy Material Jargon
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Old 07-28-2012, 03:46 PM   #1
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Default Alloy Material Jargon

Been around hunting rifles all my life, but wanting something that's totally different to play with, and like the idea of building to my likes, so I looked at some sites that sell Lower Receivers and am SO CONFUSED on some jargon.
It seems everyone touts 7075-T6 over 6061 aluminum. Ok. The number is larger, but what is the difference? Read a little about it, but it I still can't comprehend the strength difference of maybe 25%. This doesn't seem like much compared to aluminum and steel. I like steel---why NOT a steel receiver for Civilian usage? If a modern receiver isn't even made with 6061 alloy anymore why even mention it. Or are they---and who, so's I can stay away from that Manufacturer.
I know very little about Forged compared to Billet, but other than some casting seams(looks) that generally not ground off before anodizing, is there any strength differences between the two?
Just Today, I found a site that Manufacturered their own lower's and they mentioned something called "Nickel Boron". What is this, and wanting a person to get it for the extra cost? Are their other "coatings" being used in the industry that would make somebody say I have a better "SHTF" gun than you because my cash outlay was more? Why would I want/need this type coating? Is it on inside/outside/all over---what? I want a good gun, but if something is not needed, I don't want to pay for the "end of world" type car salesman BS, just to get a sale when I can save myself $150 for same type reliability in either same manufacturer, but different model/series product, or going to another Manufacturer.
Del

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Old 07-28-2012, 04:39 PM   #2
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The numbers refer to the "recipe" used for that alloy.

The alloy composition of 6061 is:

Silicon minimum 0.4%, maximum 0.8% by weight
Iron no minimum, maximum 0.7%
Copper minimum 0.15%, maximum 0.40%
Manganese no minimum, maximum 0.15%
Magnesium minimum 0.8%, maximum 1.2%
Chromium minimum 0.04%, maximum 0.35%
Zinc no minimum, maximum 0.25%
Titanium no minimum, maximum 0.15%
Other elements no more than 0.05% each, 0.15% total
Remainder Aluminium (95.85%–98.56%)


7075 aluminum alloy's composition roughly includes 5.6–6.1% zinc, 2.1–2.5% magnesium, 1.2–1.6% copper, and less than half a percent of silicon, iron, manganese, titanium, chromium, and other metals. It is produced in many tempers, some of which are 7075-O, 7075-T6, 7075-T651.

Is the difference enough to matter? Beats the hell out of me. I DO know there is a major difference between the aluminum stock used to make beer cans, and the stock used to make aircraft engines. And my beer can does not need to be as tough (or as expensive) asd an aircraft engine. But the beer can cannot be machined or polished the way the engine block can be.

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Old 07-28-2012, 04:45 PM   #3
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Go with what you want, it's your choice. But you'd be wise to stay with 7075 T6 receivers. Over 20 million made and they work. Forged vs. billet? Either works. Steel, why add weight when 7075 works so well? 6061, leave that for accessories, not receivers and the receiver extension.

ETA:

Nickel boron, you don't need it. Just buy something like BCM or Colt and you've invested well.

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Old 07-28-2012, 06:21 PM   #4
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Think Quentin may have summed it up nicely. Some of the ads I see remind my of a line from an old movie- "He's a GOOOOD coffin salesman. He can make you feel like you NEED that bronze and white satin......"

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Old 07-28-2012, 08:34 PM   #5
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C3shooter, what is it about you and great old movies!

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Old 07-28-2012, 09:44 PM   #6
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Quote:
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C3shooter, what is it about you and great old movies!
AGE.
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Old 07-28-2012, 09:55 PM   #7
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Quote:
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C3shooter, what is it about you and great old movies!
Quote:
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AGE.
now that was funny!
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Old 07-29-2012, 03:01 AM   #8
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7075-T6 has a tensile strength of 78,000 psi. Elongation failure is 3-9%

6061-T6 has a tensile strenght of 42,000 psi. Elongation failure is 10%.

So, 7075 is stronger and 6061 is more ductile.

A simplistic explanation would be if you have an application where yield / fatigue strength are important you'd use 7075, and if repeated flexing of a part was required you'd choose 6061.

7075 approaches the strength of steel which is why it's used in AR rifle receivers.

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