An aluminum keyboard is supposed to be made of aluminum, yes, some manufacturers claim they did, but only half -- the top case, the bottom case is made of plastic;
Some manufacturers do make the case full aluminum, yes, but when you find the 4 screws on the left and right side walls, like this one:
From professional manufacturers' point of view, this case is made of 4 pieces of sheet metal, fastened with screws, you will find edges on the 4 corners, neither the screws or the edges make this keyboard good looking... What's more this structure is not sturdy as it is not an entire piece of metal.
Coyres keyboard utilizes a "tray structure" as the bottom case, upper case is fastened by 8 screws hidden under the keycaps, no screws are visible on exterior case, this way the keyboard is built elegantly and solid.
Coyres... The best aluminum keyboard