Framebuilders - Al 6061 vs 7005

Which is supposed to be better for bike frames?
Is the choise to use one or t'other made on technical or business grounds?
Does it depend on the scale of manufacture, eg the size of your heat treatment oven or the warehouse space to leave your frames to age?

I'm not an expert on such matters but I do know that 6061 requires a post weld heat treat while 7005 does not. That said, 6061 is still popular among some large framebuilding houses like Cannondale. Properly heat treated 6061 is adequately strong, fairly cheap, and not overly brittle.

Check out this site for materials properties: http://www.matweb.com

Typically 7005 is about 20-30% stronger with 60-80% more fatigue resistance than 6061 with the same stiffness. It's a little harder to weld though. Yeah, and no post-welding heat-treatment necessary. I wonder if this patent has any effects on the use of 7005 in bike-frames: http://www.freepatentsonline.com/5507888.html. The royaltee fees to the patent-holder may dissuade many manufacturers from using it maybe.

Almost all frames are 7005 these days, or versions thereof, whether low-end or high-end (See: Easton Elite). 6061 is a pain in the ass, as this sad sap who's solution heat treated frames before will attest. 7005 just needs an artificial age, which is much lower temp and much easier to do than a solution heat treat followed by an artificial age.

Having said that, solutioning frames isn't a massive hurdle if you're geared up for it.

There's no royalty to be paid on 7005 frames that I know of. That patent excerpt is vague and appears to be alluding to a manufacturing process rather than an alloy type, or a combo of both. Anyone who can afford the tubes and knows how to weld can weld up a 7005 frame.

Vote #1, 7005!

No, wait! Steel is Real! :)

No, wait! Ti is Fly!

I might be wrong on this since I'm not a materials expert, but to my knowledge you don't absolutely have to post heat-treat aluminum after building.

I might be wrong on this since I'm not a materials expert, but to my knowledge you don't absolutely have to post heat-treat aluminum after building.No you don't have to heat-treat 6061 after welding. But its strength will be only 1/3 to 1/2 of the original pre-welding state.

Why deal with Aluminum. Its harder to weld, ride quality isn't as nice. The only reason I would consider Al would be for absolute highest stiffness to weight ratio at the lowest cost.

My Alum. bike (Principia) is made from 7020, not sure what advantages (if any) there are vs 7005. Any thoughts?

Jeff

Why deal with Aluminum. Its harder to weld, ride quality isn't as nice. The only reason I would consider Al would be for absolute highest stiffness to weight ratio at the lowest cost.Hmm, actually aluminium has exactly the same stiffness-to-weight ratio as steel. The harsher ride-quality is due to market demands and perception that somehow "stiffer frame is better". That's a bunch of BS and we all know it. The manufacturers just responded to that misconception and built oversized tubing frames for the higher stiffness people wanted. Aluminium just allows you to build large-diameter tubing with thick enough walls for a given weight. Steel would be impossibly thin in those diameters at the same weight as alloy.

But the early alloy frames were made with standard-size tubing as steel. Look at the Vitus-979 and Peugeot Galaxy/Comete from the '80s. They were more flexible than steel frames and ride-quality was actually better. People did complain about these wet-noodle frames but many TDF champions rode a Vitus-979 to victory. The softer frames weren't any slower.

Its harder to weld,
O'rly? :rolleyes:

Why do people assume that aluminum = stiff? The 80s aluminum frames from Vitus were skinny tubed flexy noodles, but wow! They were quite comfy on long rides. And why do people assume that steel is just the right amount of stiffness without being too stiff/harsh? If a steel frame's stiffness can be tuned with the use of larger/smaller wall thicknesses and bigger/smaller tube diameters, why can't the same be said of aluminum? There are a lot more variables involved than just the metal.

what about 6066 aluminum?