Aluminum parts

'Aluminum Alloys can be divided into nine groups.

Designation	Major Alloying Element
1xxx	Unalloyed (pure) >99% Al
2xxx	Copper is the principal alloying element, though other elements (Magnesium) may be specified
3xxx	Manganese is the principal alloying element
4xxx	Silicon is the principal alloying element
5xxx	Magnesium is the principal alloying element
6xxx	Magnesium and Silicon are principal alloying elements
7xxx	Zinc is the principal alloying element, but other elements such as Copper, Magnesium, Chromium, and Zirconium may be specified
8xxx	Other elements  (including Tin and some Lithium compositions)"

-To my knowledge most current bmx parts use 6 or 7 series, if someone finds parts using a different series please comment

"6xxx Series. Alloys in the 6xxx series contain silicon and magnesium approximately in the proportions required for formation of magnesium silicide (Mg2Si), thus making them heat treatable. Although not as strong as most 2xxx and 7xxx alloys, 6xxx series alloys have good formability, weldability, machinability, and relatively good corrosion resistance, with medium strength. Alloys in this heat-treatable group may be formed in the T4 temper (solution heat treated but not precipitation heat treated) and strengthened after forming to full T6 properties by precipitation heat treatment.

7xxx Series. Zinc, in amounts of 1 to 8% is the major alloying element in 7xxx series alloys, and when coupled with a smaller percentage of magnesium results in heat-treatable alloys of moderate to very high strength. Usually other elements, such as copper and chromium, are also added in small quantities. 7xxx series alloys are used in airframe structures, mobile equipment, and other highly stressed parts.  Higher strength 7xxx alloys exhibit reduced resistance to stress corrosion cracking and are often utilized in a slightly overaged temper to provide better combinations of strength, corrosion resistance, and fracture toughness."

-quotes taken from [ http://www.materialsengineer.com/E-Aluminum.htm ] check it out to read about the other series

6061-T6

Density: 2.70 g/cc

Brinell Hardness: 95

Yield Tensile Strength: 276 MPa

6066-T6

Density: 2.72 g/cc

Brinell Hardness: 120

Yield Tensile Strength: 359MPa

7005-T6

Density: 2.78 g/cc

Brinell Hardness: 94

Yield Tensile Strength: 290 MPa

7075-T6

Density: 2.81 g/cc

Brinell Hardness: 150

Yield Tensile Strength: 503 MPa

-to understand more about yeild strength read this http://www.tppinfo.com/defect_analysis/yield_strength.html

-As you can see those numbers are quite different and ive ran sprokets that get eat and that stay boss as fuck so look into what they are made of before you support a company