Heat treating alu bike frames

[Dingo2024]

Hi, just came across this article;

http://www.pinkbike.com/news/To-the-Point-Heat-Treating-Aluminum-Frames.html

Ian

 

[Dlogic]

Excellent article. Thank you. That´s why i´ll stick to steel when building my frames. It´s heavier but more forgiving and easier to handle.

 

[Farfle]

Excellent article. Thank you. That´s why i´ll stick to steel when building my frames. It´s heavier but more forgiving and easier to handle.

Absolutely, steel is the ideal metal for homebrew frame building. And its not heavier when done right, but doing it right requires a lot of small ladder frames and thin wall tube that's a bitch to weld.

 

[Dlogic]

Absolutely, steel is the ideal metal for homebrew frame building. And its not heavier when done right, but doing it right requires a lot of small ladder frames and thin wall tube that's a bitch to weld.

That´s true. The last build ended up with a total of 52 pieces welded together. The biggest issue was the deformation due to the heat whilst welding. But that´s where the torch and my hydraulic press come into the game.

 

[Chalo]

The process in the article is for 6061 aluminum alloy. Most commercial bike frames now use 7005 alloy, which is about the same strength as 6061, but naturally solution heat treats (the first step) at air cooling rates after welding. The frames are then artificially aged (the second step) or in the case of the least expensive frames, naturally aged by letting them sit around awhile before they are assembled and sold.

The switch to 7005 alloy was all about simplifying the heat treatment process to reduce manufacturing costs.

 

[speedmd]

Hi Chalo

I have been working with both 6061 and 7005 tubes the last 15 years and can tell you that properly tempered 7005 is way stronger, harder and resilient than the 6061 in any temper. IMO it is Not even close. All the tube makers I have dealt with classified the 6000 series are as soft alloy and the 7000's as hard alloys. Zinc in most of the 7000 series alloys adds the hardness. They artificially age (oven soak) relatively the same. The Extruders I have been working with water quench and stretch them sightly in some tempers to achieve max / various physicals.. Not sure you can do much of that once its built up in a frame. Not sure you would want to loose much of that in the tubes away from the welds if they are a good temper to start. Interesting what simple local tempers /methods could work on a frame if you want to preserve temper in the main tubes away from the welds.

 

[full-throttle]

Intense Cycles (interviewed in the article) mostly use Easton EA6X alloy for its compatibility with 6061 billet. It's also said to be stronger than 6061.

The Intense frame that I own actually started cracking on both sides in the middle of a machined part, not next to a weld

The part is simply under designed. Read the comments. Search for "Intense frame fail or crack".

Jeff Steber can talk all he wants about "heat treating in house" and "made in USA", but he will never convince me to buy Intense again. The interview is an attempt to get the reputation back.

 

[Hyena]

Jeff Steber can talk all he wants about "heat treating in house" and "made in USA", but he will never convince me to buy Intense again

Never mind that the article was written by Richard Cunningham :lol:

 

[full-throttle]

Never mind that the article was written by Richard Cunningham :lol:

I'm a bit slow today - what's the connection? :?

 

[Hyena]

Might have been a bit obscure - he was a central character in the TV show happy days.

 

[Chalo]

I have been working with both 6061 and 7005 tubes the last 15 years and can tell you that properly tempered 7005 is way stronger, harder and resilient than the 6061 in any temper. IMO it is Not even close.

The specs suggest it is closer than you think. 7005-T6 has 42,000 psi tensile yield, 6061-T6 has 40,000 psi. So that's pretty comparable, but remember: 7005 as-welded plus artificial aging (common practice in the industry) is not quite T6 temper. As-welded and naturally aged is even less so. All frames made of 6061 are manufactured in true T6 temper as far as I know.

I have not welded anything from 7005, but I can tell you from experience that a bike frame made of 7005 is no more difficult for me to align than one made of 6061.

I really like machining parts from 7075, 7050, 7040, and 7068 alloys. Those alloys are as you describe, way stronger and harder than 6061. But they can't be welded by conventional means.

I think 7005 alloy has proven to be superior to 6061 for bike frames. But that's because it costs less to produce a frame of equal strength and quality, not because the material is stronger.

 

[speedmd]

Hi Chalo

The specs are not close at all. Ultimates are some 25% stonger and the fatigue strength some 80% higher on the 005. Don't be fooled by the closeness of some of the less meaningful tensile numbers. They use it because it is way better. Raw material / tubes are much more expensive / harder to make in the 005. Thin walled bike tubes even harder. Much better when done however.

cheers

 

[Chalo]

The specs are not close at all. Ultimates are some 25% stonger and the fatigue strength some 80% higher on the 005. Don't be fooled by the closeness of some of the less meaningful tensile numbers. They use it because it is way better. Raw material / tubes are much more expensive / harder to make in the 005. Thin walled bike tubes even harder. Much better when done however.

Ultimate tensile makes almost zero difference in a bike frame. Once you yield your frame in an unplanned "event", you usually throw it away. It's really only yield that matters.

Back when Sheldon Brown was still around, he got inside-the-industry information that a run-of-the-mill Taiwanese aluminum frame cost $8 to make before painting. Materials are more expensive now, and the dollar ain't what it used to be, but even if that number is now $20, it ain't much. Those are 7005 aluminum frames. Yes, you can get as fancy as you please with thin-walled/butted/tapered/tempered versions, but that's just not the nature of most aluminum frames. They are using 7005 because it saves a step of the process, and thus saves them money.

Cannondale used 6061-T6 to bring aluminum bikes to the level of sophistication they have now. It took careful stress analysis, and elaborate forming and wall thickness manipulation, which can be done with any aluminum alloy. What I am saying is right in the data sheets: 7005-T6 is 5% stronger than 6061-T6. Whether that is "a lot stronger and harder" to you is a matter of personal judgment. To me, it's not much. And most bikes made of 7005 are not in true T6 condition, because the advantage of the alloy is getting to skip some of the normal T6 process.

The (heavy) aluminum bikes at Walmart are made from 7005 alloy. Pacific (Schwinn) and Kent (GMC) are using it for the same reason most other manufacturers are using it-- because it's cheaper for them.

7005 is better; I am with you on that point. But it is better because it's cheaper, not because it's stronger.

 

[speedmd]

Hi Chalo

Good topic. Agree, best to get the design correct and forget the fancy stuff until you work out the hot/ weak spots. Good material does not compensate for poor design.

I have test data putting 7005 t53 at over 390mpa consistently. Hard pressed to find anything in the 6061 family to get to 300mpa and that if all goes well. Yield of over 340 vs max of 275mpa, Fatigue limits of 150 vs best of 96 mpa for the 6061.

Good point on the variation in tempers in the supply chain. Agree, this is significant and can swing results quite a ways to the negative and I believe more so in the 6000 alloys.

If you were to play with something like a long x country ski poles made with each, I believe you would quickly see what I mean.

7005 will be cheaper if thats all the supplier is running as many running bike tubes are. 20000-40000 pound minimums make it hard to run too many types and no extra time. In the US the 7000 series alloys are much more money and most extruders will not deal with them as they push slow.

I would not believe anything on a w-mart bike sticker. Not anything.

 

[ions82]

The way I understand it, 7005 and 6061 weldments are pretty close in terms of their strength when they've both had PWHT. However, I don't think 7005 "loses" as much during the welding process. So, that's why cheap bikes are made out of thick 7005. If identical frames were produced out of each alloy and then heat-treated, there would (for all intents and purposes) probably be no difference in their fatigue/service life. Design and manufacturing shortcomings would probably be a bigger factor than the difference in tensile strength between the two alloys. If heat-treating facilities are available, I'd take a frame made out of either.

Also, steel/chromoly is susceptible to the same issues when it comes to welding. There will always be a heat-affected zone. With steel, PWHT can make a big difference, too. I sure wish I had an oven that was big enough to handle different types of bike frames.

 

[speedmd]

Agree, welds are soft. All else is much better on the 005. Good reading here if you not have seen this report. http://www.wpi.edu/Pubs/E-project/A...n_Optimization_for_an_Aluminum_Bike_Frame.pdf

They had to conclude it was some 10% better if I recall when they built in a frame. I view 10% as a break through in performance, 20% as revolutionary.

 

[rocwandrer]

Hi Chalo

Good topic. Agree, best to get the design correct and forget the fancy stuff until you work out the hot/ weak spots. Good material does not compensate for poor design.

I have test data putting 7005 t53 at over 390mpa consistently. Hard pressed to find anything in the 6061 family to get to 300mpa and that if all goes well. Yield of over 340 vs max of 275mpa, Fatigue limits of 150 vs best of 96 mpa for the 6061.

Good point on the variation in tempers in the supply chain. Agree, this is significant and can swing results quite a ways to the negative and I believe more so in the 6000 alloys.

If you were to play with something like a long x country ski poles made with each, I believe you would quickly see what I mean.

7005 will be cheaper if thats all the supplier is running as many running bike tubes are. 20000-40000 pound minimums make it hard to run too many types and no extravagant time. In the US the 7000 series alloys are much more money and most extruders will not deal with them as they push slow.

I would not believe anything on a w-mart bike sticker. Not anything.

Neither of these alloys has an endurance limit stress in fatigue. What do you mean by fatigue limit?

 

[speedmd]

Neither of these alloys has an endurance limit stress in fatigue. What do you mean by fatigue limit?

YES. The terms Fatigue limit, endurance limit, and fatigue strength are all used in many circles to describe roughly the same thing. Wiki has more on the terms and exact meanings. http://en.wikipedia.org/wiki/Fatigue_limit

Aluminums as most have seen, have a significantly shorter life than steel when flexed repeatedly. This coupled with it's more sudden failure mode makes this something to pay attention to when making a flexible frame such as a bike. Having had frames completely fail under me, it is something you do not wish to happen. Very different SN curves than steel.

 

[rocwandrer]

Neither of these alloys has an endurance limit stress in fatigue. What do you mean by fatigue limit?

YES. The terms Fatigue limit, endurance limit, and fatigue strength are all used in many circles to describe roughly the same thing. Wiki has more on the terms and exact meanings. http://en.wikipedia.org/wiki/Fatigue_limit

Aluminums as most have seen, have a significantly shorter life than steel when flexed repeatedly. This coupled with it's more sudden failure mode makes this something to pay attention to when making a flexible frame such as a bike. Having had frames completely fail under me, it is something you do not wish to happen. Very different SN curves than steel.

I'm assuming then from this post that it is convention where you live in the world, or possibly in your industry, to call the stress that averages 10^7 cycles to failure the "fatigue limit" for materials that don't exhibit a knee?

 

[speedmd]

Looks like a somewhat curved knee to me. Not as well formed as steel certainly. I agree that lack of a horizontal section is not a comforting graph for a bike frame builder that is using aluminum.

The terms are as it is listed in some data sheets. http://www.makeitfrom.com/material-data/?for=6061-T6-Aluminum

I have seen very little data published on the 7005 T5, but it is out there.

 

[DIY_turbo]

Interesting thread. Learned alot here. So what is the proper heat treatment of 7005 so you get the best out of it?

Oops just googled it


Artificial age for 7005 frames:
Age 6 hours at 200 degrees F (± 10 degrees F) plus 4
hours at 320 degrees F (±10 degrees F). This process
must be performed by the builder on all Easton
7005 tube sets.

 

[DIY_turbo]

When you build or repair a frame of 7005, what should be the ideal temper for the tube before welding it, should it be 0, T4 or T6?

Does this depend if I want to heat treat it the frame afterwards&

My understanding is that if you heat treat any temper of alloy after welding, you can bring it all to T6.Is this correct?

How would you do it?

 

[speedmd]

Hi DIY_turbo

I am no expert, but know enough to be dangerous. Tubing is one of the shapes that commonly is drawn (work hardened) or stretched as part of ideal temper/ heat treatment after extrusion. They give it a slight tug, something like 2%. Some places call it stress relief but it acts more as a form of grain alignment. Usually a T51 T53 or a T651 or other several digit temper designations on the extruded parts I have been getting. You can not get to the best properties of most of the alloys starting off soft and just solution treating (Oven /air quench) it after welding. You can get acceptable hardness and properties but nothing close to a seamless drawn or stretched as in a properly tempered extruded tube shape material will give. Depending on alloy and process to form the shapes, it will change the temper numbers a bit. (some more reading) http://www.engineersedge.com/aluminum_tempers.htm Talk to a good extruder and they can tell you much more. Alcoa is always a good source.

I have some experience welding aluminum but have not built any full frames out of aluminum and always used chrome moly steel in the few dozen frames I built years ago. Can not say for certain what the proposed heat treatment will do to the whole frames alignment. I would be very cautious to do a whole frame without fixturing it or at least expecting to do a bunch of bending/ straightening afterwards. I think best always to start with the best drawn/ temper grades of tubing you can still weld (Look up the material properties of the temper/grade and 10% elongation has been traditionally ideal for bike frames) and not worry about the heat effect zones other than some stress cracking you may induce from the residual weld cooling stresses. You will see these right away after cooling if it happens so you can take care of them on the spot. Just over design the joints with huge gussets and watch for cracking as the welds cool. Stagger the welds, heat/cool smaller areas and always end or start at the center line of the frame so it does not twist. This way you have the best structurally acting tubes in the middle of their spans and no worry of warping of the frame in heat treatment. You can also lightly torch weld areas as they cool (small plumbers solder torch)allowing the area to cool slowly and allow some of the critical elements to stay in solution. Keep us posted on the developments, and best wishes.

Cheers

 

[DIY_turbo]

Hi speedmd,

Thanks for the info. Useful stuff. I'll be forging ahead.

DIY_turbo

 

[John in CR]

Not that I would ever try to weld on aluminum bike, but is there a way a DIYer can tell if a frame is 6061 or 7005?