 Shares of Alcoa Corp. AA, -3.31 slumped 3.5 toward a seven-month low in afternoon trading Friday, after the aluminum producer said it will immediately start curtailing one of three smelting lines that are operating at its Warrick Operations facility in Indiana, citing operational challenges. The company said the one line, which has an annual capacity of approximately 54,000 metric tons, is expected to be fully curtailed by the end of the day. 