The first allocation of the 6 metre band was referenced by Brian G3COJ for the UK Six Metre Group, stating that the first allocation for the six metre amateur band was probably made during a conference in Washington DC 1927, when a world-wide allocation of 50 to 60 MHz occurred. Since then the 6 Metre band has been re-allocated on numerous occasions world wide due to Band 1 TV.
In Australia it's somewhat difficult to obtain with certainty when the 6 Metre band was first assigned to the Australian Amateurs, however in the official journal of the Wireless Institute of Australia listed 50 - 56 MHz allocated to Australia Amateurs on the 1st of January 1947. This essentially remained for 15 years with the exception of the top end of the band getting re-allocated on various occasions varying from 50 -60 & 50 -54 MHz.
January of 1964 the lower portion of the band 50 -52 MHz (where the majority of International DX resided) was taken away from the Australia Amateurs. The band was re-allocated to 52 - 54 MHz and this substantially reduced the ability to make DX contacts for the Australia Amateurs for that period. The 50 to 52 MHz allocation was to remain legally unavailable for 6 metre operators in Australia until 1 July 1989, some 24 years later. Breach of operating rules, such as slipping down to alert an overseas station to the presence of an opening to Australia to "QSY to 52.050" usually brought the radio inspectors down on the hapless individual. It was reported that inspectors scanned overseas magazines for any reports of 50 MHz operation by VK amateurs, during Cycle 21.
The above information was sourced from an article writting by Steve G VK3OT and Eric J VK5LP and th complete article can be found here