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Posted: 6/12/2013 11:00:37 AM EDT
| Could somebody explain the difference in these alloys? Which is better for firearms use? Thanks |
| Didn't what... was that a stupid question? Let me explain my ignorance. I've never "built" an AR but have recently decided to build a dedicated 22lr. I'm just now researching various components and I've seen these 2 alloys in billet lowers, just curious of the difference. |
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Thank you for the information. Awe don't get your panties in a wad!! That particular question is the equivalent of Ford vs Chevy around here, hang around long enough and you'll get it. Glad someone answered your question instead of just being a smartass like myself........ 
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While I don't have many posts, it all comes down to the material properties.
Here are two links to the material properties of each: 6061-T6 7075-T6 I purposely chose a site unrelated to weapons so as not to inject any agendas. Starting from the top of the tables and working down. If you look at the makeup of each allow (component and wt%) you will see that 6061 has more aluminum (Al), less Magnesium (Mg) less chromium (Cr), and less Zinc (Zn) as well as some other differences. Generally, 6000 series aluminum will do better at handling corrosion. Many boat manufacturers or builders of stuff for around the ocean will actually use 5000 series aluminum which while even softer has ever better corrosion resistance. When aluminum corrodes, it gets covered with Aluminum oxide which (when left in place) will actually inhibit corrosion. A lot of this is overcome by the hard anodizing (Type III). In above water applications, anodizing is great. But if anodizing is used underwater and is damaged, the corrosion will actually be accelerated by something called cathodic or localized corrosion so sometimes it actually better to not coat the aluminum. no need to go in to all that, but back to my original point, 6061 is better against corrosion but this is negated by the hard coat for land use. Going on to the physical properties 7075 (or 7000 series aluminum in general) had a higher tensile strength...usually almost double that of 6061 (assuming both are the same temper...i.e. T6 which has to deal with the annealing process). Here's a link with a short summary of annealing: http://www.metalreference.com/INFO_Aluminum.html. So why not use 7000 series all the time. Well if you are machining the two, 6061 is a bit easier to machine since it's not as brittle (see the Hardness numbers, higher=more brittle). 6061 is softer and more ductile. It will bend more before it breaks. For course come of this is negated if you are starting with a forged part vice a billet brick; that argument has been well discussed here and in other forums. 6061 is also much easier to weld, but usually that's not required for firearms. In small buys the cost of 6061 is about half that of 7075. In larger buys one may expect the cost difference to decrease. So for a weapon, I'd day (from the material properties) that 7000 series would be better since it's stronger for about the same weight (but higher cost). The machining difficulties can be overcome by a competent machinist. The corrosion issue is negated since you are using it above water (for the most part) and it's Type III hard coated. I would say that the answer is also proven true by the military specification (MILSPEC) of the drawing package for these rifle systems. The Gov't specifies the minimum requirement for a reason. Of course, if you don't use your weapon in combat or shoot 1000+ rounds month (and I am one of those people who has never come close to either but design the stuff those great folks use in combat), then it's quite possible that the difference between 6061 and 7076 are moot. Regards |
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That's a nice write up but the fact is the official report for the change from 6061 to 7075 states it was because of experience gained from Vietnam. The designers Stoner & Sullivan have both stated the same so I tend to go with their findings, no offense. How did this experience dictate the change ? |
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You see 6061 receivers mostly in billets and extrusions because they're much easier to machine.
7075 is better for forging, and that's what the TDP called for. If you took a rifle made from each and threw it down the driveway, they would both still work fine with the only difference being they will look like they were thrown down the driveway. When it comes to 6061 to 7075, it's more of a matter of forged versus billet. If done right, you'll need scientific equipment to tell the difference. Quoted:
Why not read my first post about the corrosion up above or better yet google the info. I didn't make it up, the jungle was eating up the AL. Their words not mine. I googled and found nothing relating to corrosion as the reason for switching from 6061 to 7075, other than a few posts speculating and people smarter than myself disputing it scientifically. Furthermore, 6061 is not corroded by water. Now if you add other metals oxidizing next to it, that's different. The closest thing I found was a picture of some corroded M16's that were left in the dirt in Vietnam for four decades and found later. |
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From a machinist's standpoint, I find that 7075 is actually easier to machine than 6061 even though 6061 is softer. The chief problem with 6061 is that it sticks to highspeed tools, while the chips of 7075 do not. The machines I use are older and designed around highspeed steel tools and do not have flood cooling available. They do not have splash shields either.
With the high RPM and power of CNC machines with carbide cutters and jets of cutting fluid, either alloy machines well. One might get a bit more production from 6061, but you won't see the advantage in fewer than 150 parts. 6061 is very easy to weld, while 7075 is essentially not weldable by normal methods. |
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That's a nice write up but the fact is the official report for the change from 6061 to 7075 states it was because of experience gained from Vietnam. The designers Stoner & Sullivan have both stated the same so I tend to go with their findings, no offense. How did this experience dictate the change ? Corrosion, as he stated earlier. |
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That's a nice write up but the fact is the official report for the change from 6061 to 7075 states it was because of experience gained from Vietnam. The designers Stoner & Sullivan have both stated the same so I tend to go with their findings, no offense. How did this experience dictate the change ? Corrosion, as he stated earlier. Do you have a link? 6061 is most comminly used in marine applications specifically for it's corrosion resistance. |
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That's a nice write up but the fact is the official report for the change from 6061 to 7075 states it was because of experience gained from Vietnam. The designers Stoner & Sullivan have both stated the same so I tend to go with their findings, no offense. How did this experience dictate the change ? This is why the the receivers material changed from 6061 to 7075. 
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That's a nice write up but the fact is the official report for the change from 6061 to 7075 states it was because of experience gained from Vietnam. The designers Stoner & Sullivan have both stated the same so I tend to go with their findings, no offense. How did this experience dictate the change ? Corrosion, as he stated earlier. Do you have a link? 6061 is most comminly used in marine applications specifically for it's corrosion resistance. Chris Bartoccis book, I believe. |
| As a former machinist I'd have to agree that I'd rather machine 7075-T6 than 6061, it gums up your end mills. 7075-T6 is much stronger than 6061, as shown in the references above. 6061 has an A rating for stress corrosion in the short transverse direction, 7075-T6 a D rating. In the aircraft biz we'd never substitute 7075 for 6061 because of a corrosion problem, that just don't make any sense to me. And I think most marine applications are a 5xxx series aluminum- better weldability and corrosion resistance than even 6061. And for beer cans, I prefer something closer to commercially pure, like 1100-H19. Drink responsibly! |
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That's a nice write up but the fact is the official report for the change from 6061 to 7075 states it was because of experience gained from Vietnam. The designers Stoner & Sullivan have both stated the same so I tend to go with their findings, no offense. How did this experience dictate the change ? Corrosion, as he stated earlier. Do you have a link? 6061 is most comminly used in marine applications specifically for it's corrosion resistance. Why don't you look up the information yourself, I found it i'm sure you can. It always amazes me how all the experts come out of the woodwork to say someone or something is wrong but won't do any research because they're mind is closed and they know better. I don't care if you're an engineer, metallurgist or rocket scientist the fact of the matter is the official Govt. report and that of the designers stated the reason for the change. There's even photos of the corrosion available but hey I wouldn't bother trying to look something up I'd just keep preaching that you know it all and it couldn't happen. |
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Quoted: Quoted: Quoted: Quoted: Quoted: That's a nice write up but the fact is the official report for the change from 6061 to 7075 states it was because of experience gained from Vietnam. The designers Stoner & Sullivan have both stated the same so I tend to go with their findings, no offense. How did this experience dictate the change ? Corrosion, as he stated earlier. Do you have a link? 6061 is most comminly used in marine applications specifically for it's corrosion resistance. Why don't you look up the information yourself, I found it i'm sure you can. It always amazes me how all the experts come out of the woodwork to say someone or something is wrong but won't do any research because they're mind is closed and they know better. I don't care if you're an engineer, metallurgist or rocket scientist the fact of the matter is the official Govt. report and that of the designers stated the reason for the change. There's even photos of the corrosion available but hey I wouldn't bother trying to look something up I'd just keep preaching that you know it all and it couldn't happen. In technical threads of old one usually provided cites when presenting claims or statements such as yours. I mean, since you looked it up and all, you either had had the links or material to cite as fact. Instead, when people asked, twice, you showed your ass. That's my opinion, no cite needed. I too am interested in the switch and the reasons why, and will look it up out of curiosity. Perhaps when I find suitable facts I'll present it in this topic.
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Could somebody explain the difference in these alloys? Which is better for firearms use? Thanks Different alloys with different makeups. There is no "better" in an all encompassing answer. For a dedicated .22, you may very well find T6061 is better, as it is cheaper and that is typically the reason for a .22 build. In terms of all out durability, the 7075 materials will hold up "better", but again, that may only be one part of the larger picture. |
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That's a nice write up but the fact is the official report for the change from 6061 to 7075 states it was because of experience gained from Vietnam. The designers Stoner & Sullivan have both stated the same so I tend to go with their findings, no offense. How did this experience dictate the change ? Corrosion, as he stated earlier. Do you have a link? 6061 is most comminly used in marine applications specifically for it's corrosion resistance. Why don't you look up the information yourself, I found it i'm sure you can. It always amazes me how all the experts come out of the woodwork to say someone or something is wrong but won't do any research because they're mind is closed and they know better. I don't care if you're an engineer, metallurgist or rocket scientist the fact of the matter is the official Govt. report and that of the designers stated the reason for the change. There's even photos of the corrosion available but hey I wouldn't bother trying to look something up I'd just keep preaching that you know it all and it couldn't happen. YOU made the claim. I googled and all I got was regurgitated trash saying 6061 rusts on gun forums, and scientic reports stating 6061 is designated marine grade aluminum due to it's high corrosion resistance. Secondly, the anodizing process should be more than capable of protecting the aluminum, even if aluminum was so easily corroded by water. 7075 is obviously stronger, but regardless of what this mythical report claims, water corroding anodized 6061 easily is bullshit. I highly suspect an issue with the finishing process not being friendly with 6061 as the real culprit. 7075 uses zinc, and is actually less corrosion resistant than 6061. Here are some articles expanding on the falsehood of your claims from the military article you say is readily available that no one else knows about first hand. http://ezinearticles.com/?Aluminum-Alloys-7075-and-6061:-Differences-and-Practical-Applications&id=7416798 http://www.aircraftspruce.com/catalog/mepages/aluminfo.php http://www2.galcit.caltech.edu/~tongc/html/data/elastic/Extruded_Alloy_6061.pdf http://www.keytometals.com/page.aspx?ID=AluminumGrades&LN=EN |
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