TECHNOLOGY STORIES BIKE INFO, GEOMETRY ... - Vintage Trek

Zirconium as the ingredient for grain control. From our
testing, zirconium seemed like it was particularly effective.
So when I decided to attempt to create an alloy specifically
for making a bike frame, I decided to get rid of the
Chromium used in 6061, and use Zirconium instead.
Since we use multiple heat treat cycles when we manufacture
a frame, we needed a high response to the heat
treatment. So I added more of the precipitation hardening
ingredients Silicon and Magnesium.
I also increased the amount of Copper, as it has a strong
strengthening effect, and the copper-based aluminum alloys
show excellent fatigue properties. So I thought more
Copper might help increase the fatigue strength of the alloy.
Another requirement we have is the ability to form the
material substantially at room temperature when it is in the
soft condition. The auto industry uses a couple of 6000
series alloys specifically designed for forming into complex
auto body surfaces. These are 6009 and 6010, sheet forming
alloys. The notable difference between these and other
6000 alloys is a significant Manganese addition. So I
added a little Manganese to the alloy to improve the forming
ability.
May I have a bit of alloy, please?
The barrier to testing a new “mix” is that you need a
good foundry to make a batch for you. A single furnace load
of material is 40,000 pounds, or 20 tons of aluminum. If
the alloy does not work out well that could be a lot of scrap.
So I made my best guess at what the percentages should be,
and had the first batch poured.
Great results
ZR9000 has worked out extremely well. It machines
cleaner and with less tearing than 6061 tubing can be
mitered with higher accuracy, and press fits (like headset
bearings) are more precise. In the annealed condition, it
forms very well which helps us make our sophisticated
chainstays. It welds very nicely, with high strength and
good cosmetic appeal. It has an excellent response to heat
treatment, which adds to our frame alignment. So compared
to 6061, it allows us to make the frame without any additional
trouble.
In a completed structure, ZR9000 tests out very well. In
tensile tests of identical complete frames, the yield strength
is about 1/3rd higher than 6061. On our fatigue testing
machines, the ZR9000 frames endure 5 times the number
of stress cycles (at the same loading) as the 6061 frames
before failure.
These results are as good as I could have hoped for.
We have been able to use the higher properties of the new
material to remove weight in places where it is beneficial
and increase the fatigue life and dent resistance of the frame
tubing.
This is the first material that I am aware of that has
been designed expressly for the process by which we make
a high performance bicycle frame and thus to optimize the
frame’s performance.
The Name ZR9000 was chosen because the small
amount of Zirconium addition for controlling the grain size
is the key that allowed us to increase the amounts of the
other strengthening additives. The 9000 is because new or
6
2002 Trek Technical Manual
experimental alloys which have not been assigned industry
numbers are designated in the 9000 series. So this is
our Zirconium grain refined, experimental alloy developed
specifically for making state of the art bicycle frames.
Even though I have been working on aluminum bike
frames for 28 years, the pace and amount of innovation has
kept it really fun. I’m sure you will enjoy using our new
products based on this material innovation