Aluminum can be divided into two major categories: wrought and casting alloys. Casting alloys, known by three number designations (1xx, 2xx, 3xx, etc.), contain a high level of silicon. The silicon gives the casting alloys low melting points and good fluidity, yet prevents a desirable finish from aluminum electropolishing.
Wrought alloys, known by four number designations (1xxx, 2xxx, 3xxx, etc.), are shaped by plastic deformation and have significantly different compositions and microstructures from casting alloys. The electropolishing of wrought alloys produces desirable results. An aluminum electropolished wrought surface will exhibit an improved microsurface and will be free of surface contaminates. The surface will also exhibit a lustrous finish, however, not to the same degree as stainless steel.