Re: Steel or Aluminum
I prefer steel because it can be welded for repairs or modifications like adding in mounting tabs or extra gussets to further strengthen the frame. Aluminum can also be welded but would need to be heat treated again or it will lose a lot of its strength... Aluminum alloys like 6061T6 are heat treated in order to enhance hardness and steength, the 2 series along with the 7 series alloys can't be welded but the 5 and 6 series alloys are easily welded. The T number at the end is the heat treatment process to give it better hardness and strength properties. 6061 is very popular for its excellent balance of strength and corrosion resistance.
7075 T6 is both harder and stronger than mild steel but needs to be protected from corrosion and will crumble to ash if welding is attempted. 2024 T3 is also very hard and strong but will oxidize if not protected by painting and will also tend to turn to an ashy mess if trying to weld or melt. 6061 isn't as strong or hard as 2024 or 7075 but it's almost as strong as mild steel and weldable, it does need to be heat treated after welding is done tho or it will be very soft at and near the welds.