Aluminum

Carbon Fiber

Carbon Steel

Titanium

Glossary of Terminology

CRANKSETS
 - Design Evolution
 - ISIS Standard
 - Crank Length
 - Ceramic Bearings

HANDLEBARS
 - Features
 - Aluminum
 - Carbon
 - Titanium

BICYCLE SEATS

SEAT POSTS

BICYCLE TIRES
- MTN Bicycle Tires
- Bicycle Tire Liners

BICYCLE TUBES
- Schreader Valves
- Presta Tube Stems
- Butyl or Latex

BICYCLE WHEELS

MATERIAL SCIENCE

Bicycle Helmets

Aluminum

Weight: Steel (approx. 8g/cm3) is twice as strong, but approximately three times as heavy as aluminum (approx. 3g/cm3), thus there is significant attraction to use aluminum in many applications where weight reduction can offer a strategic advantage... like hopping down a rugged trail on your aluminum mountain bike.

But like all good things there are trade offs. Often in order to offer the same strength as the steel equavilent, aluminum tubing must be oversized both in overall size and wall thickness. Various alloying and mechanical processing methods are used to improve the mechanical characteristics of aluminum.

Alloying: Elements like copper, magnesium, silicon, managanesse, and zinc are alloyed with aluminum to develop specific mechanical properties. Generally aluminum alloys are identified as being suitable for casting or mechanical deformation.

All alloys are indentified by a numerical code that identifies the type of impurities, their percentages and the heat or mechanical treatments applied using standard AISI/SAE designations. The first 4 digits represent the type of metals used in combination with the aluminum and the last numbers indicate the form of treatment. Here's a few examples:

1xxx - indicates >99% pure aluminum
2xxx - copper as the predominate alloy
3xxx - manganese as the predominate alloy
6xxx - Aluminium-magnesium-silicon alloys
7xxx - Aluminium-zinc-magnesium alloys ... etc.

for specifics see the aluminum.org list of registered international designations for aluminum alloysor the International Aluminum Institute for extensive information on aluminum alloy characteristics.

Typically the larger the number the higher the greater strength characteristics associated with this alloy. (ie. I have seen $300 aluminum handle bars out of Aluminum 7075 T-6 with a given tensile strength of 572MPa.. Thus it is important to not group all aluminum products in the same pot. Price should be a pretty good indication.

Tensile Strength: approximately 50MPa for basic aluminum alloys and up to 600MPa for 7000 series aircraft grade aluminum.

Modulus of Elasticity: Typically between 69 and 73 GPa depending on the specific alloy and the manufacturing process. This would suggest that aluminum is not particularly a stiff material, relative to say steel or titanium.

Fussy manufacturers of things like aluminum bike frames, will adjust tube diameters and wall thicknesses to compensate for relatively weaker metal.

Oxidation: Aluminum will corrode and weaken, although it does not create the typical ugly "rust" that we are familiar with, with iron based metals, thus it is necessary to address this issue in one of two ways. The least expensive, but labour intensive method is to lacquer or wax coat things like bicycle frames. The more industrial approach is to use a process such as aluminum anodizing.

Aluminum Anodizing: This is an electrochemical process that encourages the production of a naturally occuring, protective aluminum oxide coating. It is environmentally friendly. It produces an extremely hard and weather resistant finish that can be transparent or dye tinted for an artistic affect. The finish is unaffected by UV rays. Higher end items like a Trek aluminum bike frame or custom after-market car parts will often be anodized.

For the technically minded if you would like to see what one professor is working on at the University of British Columbia, check out this site, where he is designing metals for high performance sporting equipment ... a nanostructured metal, in this case an aluminum-scandium alloy, for high-performance aluminum mountain-bike frames.

Other interesting sites:
Alunimun Organization overview of aluminum alloys - great!

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