U.S. aluminum prices are falling despite a tariff aimed at boosting domestic production of the metal.

That’s good news for manufacturers of products such as beer cans and car hoods, which are paying 4% less for aluminum than they were before the Trump administration announced the tariff on March 1. These manufacturers said at the time that the 10% tariff on foreign aluminum could push up prices and cause a domestic aluminum shortage just as their orders pick up in a strong economy.

And...