Alcoa plunged 4.8% in Wednesday's extended trading session after providing a bleak 4Q outlook for its Aluminum business. The company said it expects a decline in the Aluminum segment from 3Q due to higher power cost projections in Europe, increased maintenance and seasonal labor costs.Meanwhile, Alcoa (AA) reported stronger-than-expected 3Q results as revenues of $2.37 billion surpassed analyst’s expectations of $2.22 billion.