DIN EN ISO 2128:2010-12

This standard specifies a non-destructive method for determining the thickness of anodic oxidation coatings on aluminium and its alloys using a split-beam microscope. The method is applicable, in most industrial cases, to anodic oxidation coatings above 10 µm, or above 5 µm if the surface is smooth. The use of the method described is only possible if both of the luminous lines described in clause 3 are clearly visible and distinctly separated, meaning not in the case of opaque or dark-coloured coatings. Problems can arise as a result of surface roughness. For split-beam microscopes, a parallel light beam falls diagonally on an anodic oxidation coating surface, normally at an incidence angle of 45°. A part of the beam is reflected at the outer face of the oxidation coating; another part penetrates the coating and emerges after reflection at the metal/coating interface and two resulting refractions. Two parallel luminous lines are obtained at the ocular, the distance between these being proportional to the thickness of the oxidation coating and to the magnification. This distance is also dependent on the refractive index of the coating, and on the geometry of the apparatus. If the incidence angle and the angle to the optical axis of the split-beam microscope are both 45°, the coating thickness is to be calculated according to equation. The International/European Standard has been prepared under the leadership of ISO/TC 79/SC 2/WG 16 "Revisions for Systematic reviewed TC 79/SC 2 ISO standards" (secretariat: JISC, Japan) in a parallel procedure with CEN/TC 132/WG 15 "Aluminium anodisation" (secretariat: BSI, United Kingdom). On the national level the responsible Working Committee is NA 066-01-09 AA "Anodisch oxidiertes Aluminium" ("Aluminium anodisation") of FNNE.