An endoprosthesis includes an expandable tubular body defined by a plurality of struts. In some embodiments, the expandable tubular body includes a bioerodible metal that has at least a first surface region and a second surface region. The first and second surface regions can have different surface oxide compositions. In some embodiments, the first portion has a thermally altered microstructure and the second portion has a wrought microstructure. The thermally altered microstructure can be a cast microstructure comprising dendritic grains. The first portion forms at least a portion of an outer surface of the expandable tubular body. In some embodiments, the expandable tubular body includes iron or a bioerodible iron alloy and at least one surface of the expandable tubular body includes a substantially uniform coating of iron(III) oxide.