It sure can - and some stars do, to a minor degree. However, it can no longer gain energy from this fusion - it costs energy to create heavier elements. --- To fuse Iron, you would need a huge amount of heat and pressure, higher than what can be provided by even the massive stars is existence. The upper limit of a stars mass puts this limit on what materials it can fuse. Elements heavier than Iron are created during a supernova explosion, the death of a massive star.