Help regarding heat treatment of 6061-T6 for a bicycle part

I have a question which I was hoping that someone here can help me with. Please forgive my ignorance
of metallurgy, as it is not my field :^)

I'm working on a bicycle handlebar, to be fabricated from 6061-T6 aluminum. While a somewhat
unorthodox (read:aerodynamic) design, my engineer designed it to have the stiffness of an equivalent
length of 1 in. diameter 6061-T6, wall thickness .08". In other words, stiffer than much of what is
out there on the market in this niche.

Here's the rub...while shopping fabricators to make my prototype bar, I have gotten a couple of
different opinions. One firm tells me that the 6061-T6 alloy loses approx 10% strength with welding.
This I can live with, as the bar has been overengineered to begin with. The rep said, "Unless you
are building an airplane out of it, don't worry".

Another firm has informed me that there will be a loss of over 50% strength, and that I absolutely
must have it heat treated (cost $200 dollars) or risk certain doom. This particular fellow has done
more bicycle work...which in one sense makes me trust him. On the other hand, the first guy was from
a pretty big aluminum fabrication house.

Would anyone care to weigh in on the subject? My R&D budget is not huge, and I will probably need to
go through a few revisions of the project based on rider input...so I am trying to be as economical
as possible. However, I will certainly spend the money to get a safe end result, as I don't want to
kill my test riders (of which I am one)!

Thanks, Phil

 

there are proprietary materials handbooks that directly and authoritatively answer these questions.

"Phil Spengler" <[email protected]> wrote in message
news:[email protected]...
> I have a question which I was hoping that someone here can help me with. Please forgive my
> ignorance of metallurgy, as it is not my field :^)
>
> I'm working on a bicycle handlebar, to be fabricated from 6061-T6 aluminum. While a somewhat
> unorthodox (read:aerodynamic) design, my engineer designed it to have the stiffness of an
> equivalent length of 1 in. diameter 6061-T6, wall thickness .08". In other words, stiffer than
> much of what is out there on the market in this niche.
>
> Here's the rub...while shopping fabricators to make my prototype bar, I have gotten a couple of
> different opinions. One firm tells me that the 6061-T6 alloy loses approx 10% strength with
> welding. This I can live with, as the bar has been overengineered to begin with. The rep said,
> "Unless you are building an airplane out of it, don't worry".
>
> Another firm has informed me that there will be a loss of over 50% strength, and that I absolutely
> must have it heat treated (cost $200 dollars) or risk certain doom. This particular fellow has
> done more bicycle work...which in one sense makes me trust him. On the other hand, the first guy
> was from a pretty big aluminum fabrication house.
>
> Would anyone care to weigh in on the subject? My R&D budget is not huge, and I will probably need
> to go through a few revisions of the project based on rider input...so I am trying to be as
> economical as possible. However, I will certainly spend the money to get a safe end result, as I
> don't want to kill my test riders (of which I am one)!
>
> Thanks, Phil

 

Phil Spengler wrote:
>
> I have a question which I was hoping that someone here can help me with. Please forgive my
> ignorance of metallurgy, as it is not my field :^)
>
> I'm working on a bicycle handlebar, to be fabricated from 6061-T6 aluminum. While a somewhat
> unorthodox (read:aerodynamic) design, my engineer designed it to have the stiffness of an
> equivalent length of 1 in. diameter 6061-T6, wall thickness .08". In other words, stiffer than
> much of what is out there on the market in this niche.
>
> Here's the rub...while shopping fabricators to make my prototype bar, I have gotten a couple of
> different opinions. One firm tells me that the 6061-T6 alloy loses approx 10% strength with
> welding. This I can live with, as the bar has been overengineered to begin with. The rep said,
> "Unless you are building an airplane out of it, don't worry".
>
> Another firm has informed me that there will be a loss of over 50% strength, and that I absolutely
> must have it heat treated (cost $200 dollars) or risk certain doom. This particular fellow has
> done more bicycle work...which in one sense makes me trust him. On the other hand, the first guy
> was from a pretty big aluminum fabrication house.
>
> Would anyone care to weigh in on the subject? My R&D budget is not huge, and I will probably need
> to go through a few revisions of the project based on rider input...so I am trying to be as
> economical as possible. However, I will certainly spend the money to get a safe end result, as I
> don't want to kill my test riders (of which I am one)!
>
> Thanks, Phil

There is a book called "Bicycle Metallurgy for the Cyclist": Written by: Douglas Hayduk,
Published by: Johnson Publishing Co., Boulder, CO, published about 1984 that would be useful if
you could find it.

Mine is in storage.

The author was a MS in Metallurgy and a bicyclist and a budding bicycle component designer.

You should also go to visit http://home.pacifier.com/~tpaterek/books.htm

The above site sells or directs you to technical information for bicycle builders.

A book is a lot cheaper than one fractured prototype.

Jim Buch

 

Phil-I believe your question could better be answered on the usenet group sci.materials,
sci.eng.metalurgy or sci.engr.joining.welding. I regularly read and post to these groups and
questions of this nature regulary come up. Why are you welding this piece? Depending on the extent
of the HAZ due to welding, I think you could easily experience a 50% strength reduction. See this
thread... http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&threadm=376541EB.60EAB639%40hsd.utc.co-
m&rnum=7&prev=/groups%3Fhl%3Den%26lr%3D%26ie%3DISO-8859-1%26q%3Dt6%2Baluminum%2Bwelding%2B6061%26bt-
nG%3DGoogle%2BSearch

rick

 

also found this...

ALCAN say 6061-T6 has ultimate strength of 38Ksi and yield of 35Ksi. For as-welded, 24 and 16 resp.
Put your welds where the stress is low and use a suitable factor of safety for the job at hand.

 

On Wed, 16 Apr 2003 19:10:51 -0500, Jim Buch <[email protected]> wrote:

>Phil Spengler wrote:
>>
>> I have a question which I was hoping that someone here can help me with. Please forgive my
>> ignorance of metallurgy, as it is not my field :^)
>>
>> I'm working on a bicycle handlebar, to be fabricated from 6061-T6 aluminum. While a somewhat
>> unorthodox (read:aerodynamic) design, my engineer designed it to have the stiffness of an
>> equivalent length of 1 in. diameter 6061-T6, wall thickness .08". In other words, stiffer than
>> much of what is out there on the market in this niche.
>>
>> Here's the rub...while shopping fabricators to make my prototype bar, I have gotten a couple of
>> different opinions. One firm tells me that the 6061-T6 alloy loses approx 10% strength with
>> welding. This I can live with, as the bar has been overengineered to begin with. The rep said,
>> "Unless you are building an airplane out of it, don't worry".
>>
>> Another firm has informed me that there will be a loss of over 50% strength, and that I
>> absolutely must have it heat treated (cost $200 dollars) or risk certain doom. This particular
>> fellow has done more bicycle work...which in one sense makes me trust him. On the other hand, the
>> first guy was from a pretty big aluminum fabrication house.
>>
>> Would anyone care to weigh in on the subject? My R&D budget is not huge, and I will probably need
>> to go through a few revisions of the project based on rider input...so I am trying to be as
>> economical as possible. However, I will certainly spend the money to get a safe end result, as I
>> don't want to kill my test riders (of which I am one)!
>>
>> Thanks, Phil
>
>There is a book called "Bicycle Metallurgy for the Cyclist": Written by: Douglas Hayduk,
>Published by: Johnson Publishing Co., Boulder, CO, published about 1984 that would be useful if
>you could find it.
>
>Mine is in storage.
>
>The author was a MS in Metallurgy and a bicyclist and a budding bicycle component designer.
>
>You should also go to visit http://home.pacifier.com/~tpaterek/books.htm
>
>The above site sells or directs you to technical information for bicycle builders.
>
>A book is a lot cheaper than one fractured prototype.
>
>Jim Buch

Absent heat treat, welded aluminum articles are anisotropic.

According to my Alcoa Aluminum Handbook (1962), 6061-T6 sheet or plate has a minimum tensile yield
strength of 40,000psi. But in the Heat Affected Zone of a weld, you don't have 6061-T6, you have
6061-T0, with a tensile yield strength of only 8,000psi. Very soft.

If heat treatment is not in the budget, perhaps a clever design can put the welds in areas of low
stress. A _really_ clever design might put the welds in locations where the forming stress is high,
taking advantage of the free extra elongation, but where operational stresses are low. For instance,
by rolling and welding round tube from sheet, then hydrostatically inflating it into an airfoil-
shaped cavity, with the welded seam oriented to form the sharper 'trailing edge'. Okay, maybe that's
_too_ clever.

-Mike-

 

I'm a machinist and I used to make custom handle bar stems out of 6061 AL. They were of custom
length and angles. I made most of them for my buddy's team, he was also a machinist in the same
shop. We made all the fixtures and had a very talented and knowledgable welder do all the welding.
We are not mechanical engineers, but we felt comfortable with the design based on our combined years
as a machinists, bike racers, mechanical type of guys, and evaluating other stems.

Anyhow, all the early ones that we did NOT heat treat (about 5-6) back to T6 condition, failed.
Fortunately, they were not catastrophic failures and we could watch the cracks forming. All the
subsequent ones that were heat treat (about 15) had a 100% non failure rate at the welds. A few
failed, but for other reasons (big time crashing mostly). We did incorporate some small
manufacturing changes, but I don't believe that added anything to the increased strength. We're
pretty sure it was strictly due to the heat treating. Also, realize that these were mountain bike
stems used for training and racing and would probably see a lot more abuse than a road stem or
handlebar.

This evidence is, obviously, anecdotal. But you do have a responsibility to make your device as
strong and safe as NEEDED. You could design and build a handlebar that could see double duty as
an ax handle for example but that type of strength is probably not NEEDED. Just add in your
safety factors.

Good luck, Skuke

> However, I will certainly spend the money to get a safe end result, as I don't want to kill my
> test riders (of which I am one)!

 

[email protected] (skuke) wrote in message news:<[email protected]>...
> I'm a machinist and I used to make custom handle bar stems out of 6061 AL. They were of custom
> length and angles. I made most of them for my buddy's team, he was also a machinist in the same
> shop. We made all the fixtures and had a very talented and knowledgable welder do all the welding.
> We are not mechanical engineers, but we felt comfortable with the design based on our combined
> years as a machinists, bike racers, mechanical type of guys, and evaluating other stems.
>
> Anyhow, all the early ones that we did NOT heat treat (about 5-6) back to T6 condition, failed.
> Fortunately, they were not catastrophic failures and we could watch the cracks forming. All the
> subsequent ones that were heat treat (about 15) had a 100% non failure rate at the welds. A few
> failed, but for other reasons (big time crashing mostly). We did incorporate some small
> manufacturing changes, but I don't believe that added anything to the increased strength. We're
> pretty sure it was strictly due to the heat treating. Also, realize that these were mountain bike
> stems used for training and racing and would probably see a lot more abuse than a road stem or
> handlebar.
>
> This evidence is, obviously, anecdotal. But you do have a responsibility to make your device as
> strong and safe as NEEDED. You could design and build a handlebar that could see double duty as an
> ax handle for example but that type of strength is probably not NEEDED. Just add in your safety
> factors.
>
> Good luck, Skuke
>
>
> > However, I will certainly spend the money to get a safe end result, as I don't want to kill my
> > test riders (of which I am one)!

Jusst a thought, but is there a reason you can't use thicker Al or even steel to perfect the
design? Then use 0.08" T-6 for the finalized shape. Don't forget 50 yrs ago almosst all handlebars
were steel. Not that I would want to use one today for an extended period. But to perfect a
design, why not?

 

[email protected] (skuke) wrote in message news:<[email protected]>...
> I'm a machinist and I used to make custom handle bar stems out of 6061 AL. They were of custom
> length and angles. I made most of them for my buddy's team, he was also a machinist in the same
> shop. We made all the fixtures and had a very talented and knowledgable welder do all the welding.
> We are not mechanical engineers, but we felt comfortable with the design based on our combined
> years as a machinists, bike racers, mechanical type of guys, and evaluating other stems.
>
> Anyhow, all the early ones that we did NOT heat treat (about 5-6) back to T6 condition, failed.
> Fortunately, they were not catastrophic failures and we could watch the cracks forming. All the
> subsequent ones that were heat treat (about 15) had a 100% non failure rate at the welds. A few
> failed, but for other reasons (big time crashing mostly). We did incorporate some small
> manufacturing changes, but I don't believe that added anything to the increased strength. We're
> pretty sure it was strictly due to the heat treating. Also, realize that these were mountain bike
> stems used for training and racing and would probably see a lot more abuse than a road stem or
> handlebar.
>
> This evidence is, obviously, anecdotal. But you do have a responsibility to make your device as
> strong and safe as NEEDED. You could design and build a handlebar that could see double duty as an
> ax handle for example but that type of strength is probably not NEEDED. Just add in your safety
> factors.
>
> Good luck, Skuke
>
>
> > However, I will certainly spend the money to get a safe end result, as I don't want to kill my
> > test riders (of which I am one)!

Jusst a thought, but is there a reason you can't use thicker Al or even steel to perfect the
design? Then use 0.08" T-6 for the finalized shape. Don't forget 50 yrs ago almosst all handlebars
were steel. Not that I would want to use one today for an extended period. But to perfect a
design, why not?

 

[email protected] (skuke) wrote in message news:<[email protected]>...
> I'm a machinist and I used to make custom handle bar stems out of 6061 AL. They were of custom
> length and angles. I made most of them for my buddy's team, he was also a machinist in the same
> shop. We made all the fixtures and had a very talented and knowledgable welder do all the welding.
> We are not mechanical engineers, but we felt comfortable with the design based on our combined
> years as a machinists, bike racers, mechanical type of guys, and evaluating other stems.
>
> Anyhow, all the early ones that we did NOT heat treat (about 5-6) back to T6 condition, failed.
> Fortunately, they were not catastrophic failures and we could watch the cracks forming. All the
> subsequent ones that were heat treat (about 15) had a 100% non failure rate at the welds. A few
> failed, but for other reasons (big time crashing mostly). We did incorporate some small
> manufacturing changes, but I don't believe that added anything to the increased strength. We're
> pretty sure it was strictly due to the heat treating. Also, realize that these were mountain bike
> stems used for training and racing and would probably see a lot more abuse than a road stem or
> handlebar.
>
> This evidence is, obviously, anecdotal. But you do have a responsibility to make your device as
> strong and safe as NEEDED. You could design and build a handlebar that could see double duty as an
> ax handle for example but that type of strength is probably not NEEDED. Just add in your safety
> factors.
>
> Good luck, Skuke
>
>
> > However, I will certainly spend the money to get a safe end result, as I don't want to kill my
> > test riders (of which I am one)!

Jusst a thought, but is there a reason you can't use thicker Al or even steel to perfect the
design? Then use 0.08" T-6 for the finalized shape. Don't forget 50 yrs ago almosst all handlebars
were steel. Not that I would want to use one today for an extended period. But to perfect a
design, why not?

 

As your budget is limited, ask if they can do the heat treatment at the same time as another job.
Although you may have to wait a few days or a couple of weeks depending on where you get it treated
and how often they do 6061-T6. Most heat treatment ovens at the foundries I deal with are big enough
to drive a forklift into so a handlebar won't take up much space. If they do just your job they
still have to use enough energy to heat the same big oven for the several hours needed.

If you bring this up with the salesman than I'm sure they can adapt for you and see the sense in
supplying the service on a cost share basis with another client.

Or, someone could be good enough to give the temperature specs and times for the T6 treatment and
you could do it at home with handlebars, a thermometer and an extra element for your oven so you can
get it hot enough.

Hope this helps, Peter

 

I just wanted to thank everyone for their comments/assistance. I am going to talk to some places
about cost-sharing with some other projects when they go into the oven. Meantime, I'm going to see
about having the project done in T4, and then doing the aging to t6 myself in my own oven, which one
very helpful person suggested by email.

Thanks again, Phil

 

Get a book on TIG welding Al. The proper techniques (preheat, interpass heat, and post heat) can
make a big difference.

Phil Spengler wrote:

> I have a question which I was hoping that someone here can help me with. Please forgive my
> ignorance of metallurgy, as it is not my field :^)
>
> I'm working on a bicycle handlebar, to be fabricated from 6061-T6 aluminum. While a somewhat
> unorthodox (read:aerodynamic) design, my engineer designed it to have the stiffness of an
> equivalent length of 1 in. diameter 6061-T6, wall thickness .08". In other words, stiffer than
> much of what is out there on the market in this niche.
>
> Here's the rub...while shopping fabricators to make my prototype bar, I have gotten a couple of
> different opinions. One firm tells me that the 6061-T6 alloy loses approx 10% strength with
> welding. This I can live with, as the bar has been overengineered to begin with. The rep said,
> "Unless you are building an airplane out of it, don't worry".
>
> Another firm has informed me that there will be a loss of over 50% strength, and that I absolutely
> must have it heat treated (cost $200 dollars) or risk certain doom. This particular fellow has
> done more bicycle work...which in one sense makes me trust him. On the other hand, the first guy
> was from a pretty big aluminum fabrication house.
>
> Would anyone care to weigh in on the subject? My R&D budget is not huge, and I will probably need
> to go through a few revisions of the project based on rider input...so I am trying to be as
> economical as possible. However, I will certainly spend the money to get a safe end result, as I
> don't want to kill my test riders (of which I am one)!
>
> Thanks, Phil