Suggested aluminum: PLATES: 6061-t6 or 5083, ANGLE: 6063
Cast aluminum will have the best flatness
Like steel, all aluminum grades have roughly the same stiffness.
However, the grade and heat treatment of aluminum DOES matter if you plan on fabricating the plates yourself. Aluminum grades vary in their machinability.
Disregard strength properties.
6061-t6 has adequate machinability and great corrosion resistance. It it also inexpensive and ubiquitous, being the most used aluminum. There is also 5083 aluminium used by many to produce the Face plate and Tram plate.
https://www.ryerson.com/resource/the-gauge/aluminum-bar-which-grades-make-the-grade
Suggested Thickness Min -10,5mm Max -15mm, the sweet spot is around 12,5mm
Suggested Thickness Min -5mm Max -8mm, suggested is 6mm
Most alloys will work. 6061 will work but needs the interior radius to be filed down to prevent interference with fasteners (IMAGE HERE)
6063 often comes with a square radius corner, which prevents the need for filing.
https://www.steelplates.in/suppliers/czech-republic/aluminium-sheets-plates-coils-in-czech-republic/