Not sure they would be 'pure aluminium’ as this is too soft to manufacture a wheel rim. The majority of current OEM fit and aftermarket wheels are of an aluminium alloy of some sort. Aircraft standard is probably the best where the aluminium is mixed with quantities of magnesium, copper and manganese to improve its tensile strength and resist corrosion but you pay for it in terms of overall cost. Cheap aftermarket rims are probably made of a cheaper aluminium alloy. Of course you could by magnesium alloy rims to reduce un-sprung weight but the cost......!