March 12 (Reuters) - Australia's Alumina Limited said on Tuesday it has agreed to be acquired by U.S. aluminium producer Alcoa for a $2.2 billion all-stock buyout offer.

The terms of the deal are consistent with Alcoa's offer for Alumina announced on Feb. 26, when Alcoa's CEO William Oplinger told analysts the deal would eliminate Alumina's overhead costs of A$12 million ($7.93 million) a year.

Under the deal, Alumina shareholders would receive a consideration of 0.02854 Alcoa shares for each Alumina share they hold, implying a value of A$1.15 per Alumina share, based on Alcoa's closing price as of Feb. 23.

Once the deal closes, Alumina shareholders on the date of record will own about 31.6% of the merged entity, while existing Alcoa shareholders will hold 68.4%.

Alumina's board, including its Managing Director and CEO, recommend that shareholders vote in favour of the deal, in the absence of a superior proposal.

Alumina's only asset is a 40% stake in the Alcoa World Alumina and Chemicals joint venture, which is controlled by Alcoa and has interests in bauxite mining, alumina refining and aluminium smelting across Australia, Brazil, Spain, Saudi Arabia and Guinea. ($1 = 1.5126 Australian dollars) (Reporting by Roushni Nair in Bengaluru; Editing by Krishna Chandra Eluri)