So ok, I'll go for 1,5 mm aluminium but am not sure
what grades might be available here in Belgium,
not even sure we have the same codification.

Europe uses the same codification for aluminum alloys, the full name
you would be looking for is "EN AW-6061T6" (AW for wrought aluminum),
which corresponds to "EN AW-Al Mg1SiCu" (for sheet metal see European
norm EN 485, for bars see EN 754 and 755).

Oliver