The company said Apollo Global Management was now the majority shareholder in a new holding company for AEP, with a 51% stake.
Fonds Strategique d'Investissement had 10% of AEP and Rio Tinto held 39%.
Rio Tinto said the terms of the transaction were confidential.
"The closing of our majority divestment in AEP marks Rio Tinto's exit of substantially all downstream businesses," subsequent to its takeover of Alcan in 2008, Rio Tinto chief financial officer Guy Elliott said in a statement.
"Since 2008, we have completed divestments in excess of $11bn," Mr Elliott said.