The Sunday Times recently ran a report on the recommended metal for your garden furniture and Cast Aluminium won hands down.
It is the obvious choice of metal. It wil not rust, it is strong, it is not too heavy to move around (make sure you choose a thick enough casting so that it is not too light. If it blows over in the wind it could crack.)
Cast Iron or wrought iron was the popular choice of metal garden furniture in the 60s and 70s but times have moved on and most people are opting for aluminium.
Metal furniture still has huge advantages over wood. It needs little to no maintenance, it is easy to clean, it dries quickly so that you can use it straight after a rain shower and it will last you much longer than a wooden set.
So think Metal garden furniture, think Cast Aluminium Garden Furniture