Alcoa Corp, the giant American aluminum manufacturer, has asked the US Commerce Department to exclude some of its Canadian aluminum imports from tariffs. Alcoa filed five requests asking for waivers from the administration's 10 percent tariff on imports of the lightweight metal. That prompted retaliatory moves as the EU imposed 25 percent tariffs on $3.3 billion worth of US imports starting June 22. Mexico imposed tariffs on pork bellies, apples, grapes, cheeses and flat steel. Canada also imposed tariffs on American steel, aluminum and other products.