Some aluminums are not maliable(sp?) and cannot be welded. 6061 is weldable and is used in many high end bicycles and aircraft. 6075 is not weldable if I remember correctly.

What are you looking to make Bowman? Spinpole?

T6 Heat Treatment is a specific heat treatment process which may be applied to aluminum / copper / silicon alloys, such as hypereutectic, to increase the strength of the alloy by as much as 30%. In the case of T6 heat treatment, the process occurs in two phases.

The First Phase of T6 heat treatment is called the Quench Phase. In this phase the alloy is heated to 920 degrees Fahrenheit for 9 hours causing the copper in the alloy to become dissolved in the aluminum and forming what is called a "Single Phase Alloy". If allowed to air cool naturally, the copper will tend to reconstitute, or reform itself within the alloy. However, when the heated alloy is cooled rapidly by water quenching the reformation of the copper is retarded and the aluminum, supersaturated with copper, is locked into the "Single Phase Alloy" state.

Precipitation
In the Second Phase of the T6 heat treatment process, called the Aging Phase, the alloy is heated to 350 degrees Fahrenheit for 10 hours and then allowed to air cool. During this phase the copper combines with the aluminum in a process called "precipitation hardening" to form a copper aluminum crystal, CuAl2. It is the formation of these copper aluminum crystals which gives the alloy its strength.

The key to maximizing alloy strength comes from controlling the size of the copper / aluminum crystals. Maximum strength is attained when the size of the crystals, or precipitated particles, is kept very small forcing them to conform to the structure of the aluminum.

The end result is an aluminum alloy, or hypereutectic piston, that is up to 30% stronger.