The offer, originally announced on 18 August, was cleared by the European Commission but is yet to be cleared by the US Department of Justice.
Since February 2008, Rio Tinto has announced asset sales of $10.3bn, as it attempts to drive down its debt levels, which increased after its $38bn takeover of Canadian producer Alcan in October 2007.
It has been seeking to sell non-core assets acquired from the Alcan purchase. If the sale proceeds, Amcor will buy the Alcan Packaging global pharmaceuticals, global tobacco, food Europe and food Asia divisions.