We Use 6061-T6, WHY ?
it's often used in truck bodies, and semi truck trailers, East Manufacturing uses it in there Main beams and the structural cross members.
6061 is a precipitation-hardened aluminum alloy, containing magnesium and silicon as its major alloying elements. Originally called "Alloy 61S", it was developed in 1935. it has good mechanical properties, exhibits good weldability, and is very commonly extruded.
T6
the T6 refers to the temper or degree of hardness, means that the aluminum alloy has been given a solution heat treatment followed by quenching, cooling, and aging. Artificially aging allows the material to achieve the desired precipitation hardening.