Sinking aluminum prices and a ballooning surplus of the metal have deepened the industry’s worst crisis in years, intensifying pressure on high-cost smelters to embark on another round of production cuts to revive prices from their malaise. The 25 percent drop since last September has pushed benchmark London Metal Exchange prices to six-year lows, and the unprecedented plunge this year in premiums, surcharges paid for physical delivery, to their lowest in 3-1/2 years are the biggest test for producers’ margins since the 2008 financial crisis. More than 10 percent of smelting capacity outside of China, or 3.5 million tonnes of production, is running in the red with a combined LME and U.S. premium of $1,800 per ton, according to Wood Mackenzie data from second-quarter results. […]