A news release didn't disclose terms. But the Pittsburgh aluminum major said the sale would prompt it to take third-quarter charges of 54 cents to 75 cents a share.
The plants include casthouses at both facilities and a paste plant at La Coruña. Those plants are currently operating.
The transaction also includes two smelters, which Alcoa had curtailed but kept in restart condition if it found a buyer.
Alcoa said that it and the workers' representatives had reached an accord regarding the deal with Parter.
The deal is subject to Parter arranging a credit facility to support future operations.
And if the two sides can't close the purchase by the end of this month, a collective dismissal and social plan should go into effect on Aug. 1, 2019.
Alcoa said in its fourth-quarter 2018 earnings report that the social plan "preserves a portion of the jobs at the two facilities and includes retirement packages and potential relocation to the company's San Ciprián facility."
Alcoa shares were trading up 1.3% to $23.00 on Friday morning. Shares are down 13.5% for the year.
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