Aluminium for a bar wouldnt be very useable in most cases. Titanium bars still have a tendancy to break. On a disc, it would be good if it was made in a warhead/360 type fashion with an alumium disc with a full steel ring bolted around the outside that takes the loads.
Unless its a very high grade aluminium such as 7075/2014 then it wouldnt be upto the job for spinners.