Bicycle Framebuilding – Magnesium and Aluminum Compared and Contrasted

by Sabinna on May 25, 2010

I recently posted some thoughts on the use of magnesium in frame-making. In that post I quoted technologist Josh Deetz of Deetz Design & Development Co., Ltd, based in Taichung County. Here Josh guest posts in a response to my original post. Further detailed information on magnesium available at magnesium.org

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By JOSH DEETZ

I enjoyed your story about magnesium and agree with your comments for the most part. One of the issues that plagued aluminum bicycles was willingness to re-engineer the bike frame. Earlier consumer misconceptions forced a market based approach to design of early aluminum frames. Klein and Cannondale arguably were instrumental in making welded frames initially of interest by appealing to the thought that aluminum would eat energy, overly stiff frames followed and this was no longer the concern.

Between the introduction of Klein and Cannondale I worked on frames using matched properties rather than exaggerated properties. Knowing this Baby bear approach was just right, I worked without concern in USA and then pioneered aluminum frame manufacture in Taiwan spreading gospel of right sized frame tubes. I Met with Alcoa wrought alloys division and laid out my vision for 60% of the performance market of bike frames to be aluminum, I was not taken seriously to say the least.

Initially frame alignment was an issue in Aluminum frames caused mostly by welding warpage, later only post welded heat treatment caused tube warpage. Klein and Cannondale found routes of correction to address these problems. Most of these were a pound of cure. This made Aluminum bikes exclusive.

By the mid 1980’s I developed three means of avoiding the above defects, and implemented these in Brazil and Taiwan. Although companies in both places were slow to learn (very slow) over time they made aluminum frames according to my methods. By 1991 aluminum frames were on the way to becoming commonplace.

It becomes easy to see why a metal that is thought to be explosive, un-weldable, extruded by less than 10 companies worldwide, forged by less than two dozen, while weld rod is only available from 3 makers and not all weldable alloys are available, is not popular. These are the most problematic issues facing magnesium.

Add to this the fact that it is 30% lower modulus, and not as tolerant of sloppy practices. Compare this to Aluminum which took a total of 8 years to become commonplace, considering it is non corrosive in most environments can be polished, anodized, painted and it extruded by no less than 300 firms world wide. 10’s of thousands of companies forge and machine Aluminum. Ignorance was the only thing holding aluminum back, design, application and processing was all known widely, but not known to the bike builders. Once these were known it was simple.

Aluminum was not as tolerant as chromoly or hiten steel in manufacturing. Process discipline was learned because a market was made by Klein and Cannondale, once proven the Taiwanese could step in, they misstepped a few times and finally got it right. Magnesium has yet to have successful pioneer. One that communicates with knowledge, and offers products of interest.

Magnesium requires discipline in processing, 10x the chemical purity, 8x the extrusion control, absolutely strict swarf management and machining care. Welding is easier but like jumping from steel to Aluminum one must be a great aluminum welder to make a good magnesium weld.  Magnesium welds need much less heat input, faster hands, and less common gas mixtures (more costly). Finishing requires very strict discipline, without proper passivation (like steel) corrosion will always occur. Regardless of paint system magnesium will corrode if not passivated. This was ignored by nearly every company trying to make magnesium frames.

Apro, and Hodaka have only made sample quantities, while Litech, Loadstar, Merida and Pinarello made serial production. Each of these companies stopped for slightly different reasons, but really one reason ignorance of material process requirements.

Until someone decides to follow each rule and deliver meaningfully improvements over Aluminum, Magnesium will remain obscure. As a technologist I try to be the silent hand behind manufacturers, but as long as manufacturers remain unwilling to refresh the concepts of a metal frame. Top brands working on Magnesium avoided magnesium specific requirements when making frames.

Simple ideas like 1 3/8″ tubes rather than 1 1/2″ or 1 3/4″. Fear of clients thinking Mag in 1 3/4″ will be too stiff like aluminum rather than understanding 30% lower modulus means it will feel like a smaller tube in aluminum. When these simple concepts are thought to be above the consumer’s education, it can be shown to be factual. Not everyone is an early adopter and not everyone understands all these details. Many can understand and these are the people who seed the market.

Properly high end and better Magnesium frames are important. Paketa’s use of a 1930’s alloy AZ61 means the material is only lower density, strength to weight of this alloy is not as high as 6061. This alloy being susceptible to stress corrosion cracking only complicates issues this much more. s:w of AZ61 is 92, 6061 is 101 and current magnesium’s are 150. These alloys are 50% lower corrosion, 100% higher ductility.  It would be as if initial Aluminum frames were launched with 6063. New risky, lower strength, higher weight and higher costs. Magnesium made until now have been lower strength, higher weight and higher cost, as well as higher corrosion.   Why not successful ?

Simple no ?

As you said mag will come, in time, what percentage of the market, what level of performance is up to the developers. It will never replace aluminum, but will in my opinion be a market size roughly the size of steel frames or Titanium frames.

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{ 1 comment… read it below or add one }

Rae Merrill May 28, 2012 at 5:17 AM

Interesting. My magnesium road frame manufactured by Merida has just cracked where the crossbar meets the seat tube, just above the weld. Had the bike for 7 years but summer use only.

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