Aluminum is a poor material choice for thick radiation shielding, since it produces lots of secondary radiation and it's inefficient due to its high atomic mass. Polyethylene, which is nice and hydrogen-rich, is widely understood to be superior.

An aluminum hull is nice because it does double duty, but you don't need to make it thicker than the structure requires just for radiation purposes. Instead you would add internal shielding. It's also smart to use food (and the resulting waste) and other consumables as shielding, since you need to carry that mass anyway.