Grades of Aluminum

[sfca]

Metallurgists and metalworkers:

Can you explain the differences in the grades of aluminum used in flashlights and their application in the real-world?

For example, how would a higher grade aluminum carry over in a noticeable effect in the application of a flashlight for different purposes?

Fenix: 6061-T6
Surefire: 6020
Tiablo: 7075

 

[jchoo]

I think a good generalization to make about aluminum alloys is that the higher the number, the harder (stronger) it is - but it is also not as malleable (tough, able to dent or bend instead of break). The T is the temper, or heat treat of the billet as it is produced. 6061-T6 is a fairly common, but good, alloy. The 6000 series alloys used by Fenix and Surefire are in the same family, but have slightly different percentages of ingredients.

 

[LukeA]

Also, in general, the harder an alloy is, the worse its heat and electrical conductivity.

 

[sfca]

Does that mean light output would decrease as the LED heats up?
A hot flashlight isn't good but I'd assume the heat has to go somewhere.

Or am I confused? A harder alloy doesn't conduct but it doesn't insulate either.

 

[65535]

Non of the aluminum used by reputable manufactures will have signifcantly different thermal and electrical characteristics. There isn't a large enough difference in strength between the alloys to make a difference in flashlights.

Basically it comes down to what it's made out of, has no effect on the product. Though if too soft threads wear out, generally a heat treated alloy is appropriate.

 

[Mick]

Here is a nice chart from McMaster-Carr.

http://www.mcmaster.com/param/html/aluminum/default.htm

 

[sfca]

The chart explains it well. Interestingly enough, 6020 grade would be a compromise between 6061 and 7075 in hardness and yield strength.
So, higher number isn't always the best.

If a flashlight made out of 7075 grade aluminum would be more brittle then maybe I wouldn't want one cause dropping and chipping it is what I'd fear the most.

 

[gadget_lover]

The numbers describe the types of materials in the alloy. They do not have a direct relationship to a particular strength or stiffness. The number on the dash at the end describes the tempering process.

At the moment, the wiki article at http://en.wikipedia.org/wiki/Aluminium_alloy#Alloy_designations describes what goes into which alloy.

In general, if the light will be anodized you need something that does not have a lot of copper (20XX series or 30XX series)

I built a very nice light from 2011-t3. I chose that alloy because I was not going to anodize it and because it's 20% harder than 6061-t6. The 2011-t3 stood up to scratches better than the 6061.

It was a small light that I wanted as thin as possible. That meant that I had some very thin parts that would have deformed too easily if made from 6061.

I could have made it from 7075, but I liked the way 2011 machined. And I had a stick of 2011 to try out. :)

Daniel

 

[Marduke]

I think a good generalization to make about aluminum alloys is that the higher the number, the harder (stronger) it is - but it is also not as malleable (tough, able to dent or bend instead of break).

Not quite. Also, don't confuse toughness with hardness or strength, as while there is often some general trends, they are independent values.

The numbers describe the types of materials in the alloy. They do not have a direct relationship to a particular strength or stiffness.

Beat me to it.

The chart explains it well. Interestingly enough, 6020 grade would be a compromise between 6061 and 7075 in hardness and yield strength.
So, higher number isn't always the best.

If a flashlight made out of 7075 grade aluminum would be more brittle then maybe I wouldn't want one cause dropping and chipping it is what I'd fear the most.

But it would have excellent wear resistance of the threads vs a softer alloy. Dropping and "chipping" would be very unlikely, but denting would definitely be LESS likely with a harder alloy.

But there are LOTS of choices. Last I checked, there are over 20,000 flavors of aluminum alloys, so selection is anything but limited.

 

[sfca]

I get what your saying.
What would be the chance of chipping a crenelated bezel with a harder alloy vs a less harder alloy, and those vs stainless steel (relatively).

 

[Marduke]

I get what your saying.
What would be the chance of chipping a crenelated bezel with a harder alloy vs a less harder alloy, and those vs stainless steel (relatively).

I have yet to see a light that was "chipped". Dented and gouged (material deformed, but not missing) is MUCH more likely.

 

[combinatorix]

7075 is the clear winner in the strength and hardness. It is true that 7075 is more brittle, but unless you are applying repeated bending loads to your flashlight it probably won't make a difference. Aluminum is still quite soft in the grand scheme of things.

Corrosion resistance and machinability are all good, and not that relevant to the buyer.

It would be interesting to see if there are any differences in heat conduction. I suspect they are very similar.

7075 is generally more expensive than 6061, both are more common that 6020. I've never bought 6020 for anything, so I can't comment on that. For most purposes out there 6061 has more than sufficient properties (can be welded too), and it's relatively cheap and very common, which is why it logically ends up as a flashlight alloy. Once hard-anodized, it's all going to be pretty similar though. Hardness/strength is not really an issue, as I doubt many people ever run into the issue of bending or denting their lights. The coating will be the same, and the HA chipping will be the same as well.

Even so, I'd expect to see more 7075 for the high-end flashlight market. In the mass-produced state it'd likely be adding less than a dollar to $50+ product.

 

[HarryN]

I built some lights from 7075, 6061, and did some small amounts of machining with the 2011 alloy that gadget_lover likes to use. (guess where I was machining it at)

IMHO, 6061 is a PITA for a beginner to use, despite its common usage in all kinds of products. The chips tend to get long, it gums things up, etc. (So - now you know how poor my craftsmanship skills are. :sssh: )

The other two alloys machine MUCH better - almost no comparison for cutting cleanly and user friendly chips.

The 6061 light body I have is easily scratched up, but also easily sanded back into shape, as long as it is not anodized of course.

The 7075 based light body I have is just an amazing beater. Even thin sections are seriously strong, and it wears very well. After several years of EDC and random lost and found, it looks fine - even bare metal.

If you look at the properties of fully tempered 7050 and 7075, they are not all that different than cold rolled steel, sans the rust and with better thermal properties. The nice thing as well, is the ability to anodize the 7000 series materials vs the 2000 series.

I do have to say though, that the lights gadget lover has made from the 2011 came out very nice, and hold up very well in a bare metal format.

 

[sfca]

In terms of weight 2 flashlights the same weight but made of 7075 and 6061, the 7075 would be stronger and harder - but what about using the properties of 7075 to make a lighter flashlight that's still wins in strength and hardness.

Is there a enough difference to make this possible?

 

[gadget_lover]

Yes, there is that much difference. 7075 is close to twice as hard as 6061.

You can make many parts (barrel, head, bezel) thinner using 7075 yet still have the same strength. Because it is lighter, it sustains less damage when it's dropped.

It helps if you analyze what parts of the light will have the most impacts (bezel and tailcap) and make them thicker or stronger. Some areas, like the heat sink or body will take relatively little punishment.

Daniel


Daniel.

 

[sfca]

One more question gadget lover. Would you be able to tell off-hand what grade of aluminum something is made from, with experience and without use of tools. Something perhaps that we could pick up over time?

Cheers.

 

[gadget_lover]

The apearance will not tell you anything. The amount of alloying components are so small that they do not discolor it much.

There are ways to catagorize them using simple scratch tests. I'm pretty sure that tempered 7075 should be harder than a standard straight pin, so the pin will not scratch it. Some of the 2XXX and 3XXX series are pretty gummy, so a file will gum up pretty fast.

I always look at the numbers inked along the side of every stick. :) That's the easy way.

That said, I do seem to tell the difference between the 2011 leftovers and the 6061 bits, though I do not know why.

Daniel

 

[precisionworks]

6061 is a PITA for a beginner to use, despite its common usage in all kinds of products.

+1

6061 is a PITA no matter what your level of experience. Because it's soft (in a relative sense, compared to 7075), tools need to be razor sharp, coated, lubed, and run at the correct SFPM. Whenever drilling 6061, use either a brand new twist drill or one that is freshly sharpened - and the lands need to be in good shape as well. If the lands are worn, hole finish will be awful even with sharp cutting lips. Coatings are really helpful, like the Guhring Firex, as they help avoid BUE (built up edge). Once the tool gets BUE, everything starts to go downhill. Lubrication, like Tap Magic for aluminum, makes a huge difference compared to dry machining.

Correct SFPM is sometimes tough to achieve, as some aluminum tooling will run at 2000+ SFPM. On a small drill or end mill this means spindle speeds above 10k rpm, which is not an option for most of us.

FWIW, if you like to study about metals, get a copy of Metals Handbook Desk Edition. The latest version is $250, but the earlier first edition (1984) is available from Abebooks or Alibris for under $30.

 

[tino_ale]

Basically it comes down to what it's made out of, has no effect on the product.

And what data would back up this theory???

As far as I know, the ability to resist to scratches and dents, for example, is directly related to hard numbers which are the alloy characteristics. I think a customer will find resistance to dents and bumps quite relevant about a flashlight.

Some good info came out of a thread I started a while back about this question.
http://www.candlepowerforums.com/vb/showthread.php?t=176992

 

[65535]

My point is as long as a proven alloy is used, it doesn't really matter what a reputable maker uses in a flashlight, it's not a load bearing device all it has to do is hold threads and usually be anodizable. There isn't enough of a difference in the common alloys to make a marked difference in the product.