ASTM_B_681_-_88_1994.pdf

Designation:B 681 88(Reapproved 1994)Standard Test Method forMeasurement of Thickness of Anodic Coatings onAluminum and of Other Transparent Coatings on OpaqueSurfaces Using the Light-Section Microscope1This standard is issued under the fixed designation B 681;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon(e)indicates an editorial change since the last revision or reapproval.1.Scope1.1 This test method covers a procedure for the nondestruc-tive measurement of the thickness of transparent anodiccoatings on aluminum articles by means of the light-sectionmicroscope.This method may also be used to measure thethickness of any transparent coating on an opaque reflectivesurface.1.2 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2.Referenced Documents2.1 ASTM Standards:B 244 Test Method for Measurement of Thickness of An-odic Coatings on Aluminum and of Other NonconductiveCoatings on Nonmagnetic Basis Metals with Eddy-CurrentInstruments2B 487 Test Method for Measurement of Metal and OxideCoating Thicknesses by Microscopical Examination of aCross Section2B 588 Test Method for Measurement of Thickness of Trans-parent or Opaque Coatings by Double-Beam InterferenceMicroscope Technique22.2International Standard:ISO 2128 Anodizing of Aluminum and Its AlloysDetermination of Thickness of Anodic Oxide CoatingsNondestructive Measurement by Split-Beam Microscope33.Summary of Test Method3.1 The thickness of a transparent anodic coating or othertransparent coating is determined by a microscopical method inwhich a thin beam of light is projected on to the specimensurface at an angle of 45 to the normal.The displacementbetween the rays reflected from the coating surface and fromthe coating-substrate interface is measured and is directlyrelated to the coating thickness.4.Significance and Use4.1 The test method describes a rapid and nondestructiveprocedure for measuring the coating thickness of anodic oxideson aluminum and of other transparent coatings on opaquereflecting surfaces.4.2 This test method is suitable for quality control purposeswithin manufacturing operations and for determining whethercoated parts meet coating thickness requirements provided inapplicable specifications.4.3 The test method is limited by the following restrictions:4.3.1 The coating must be sufficiently transparent to allowthe light from the instrument to reflect off the coating-substrateinterface and be visible as a distinct line.4.3.2 Both the coating and substrate must be sufficientlysmooth to allow the beams of light to reflect from the coatingsurface and the coating-substrate interface without significantdistortion or aberration and to be clearly visible.4.3.3 The index of refraction of the coating material must beknown.4.3.4 The coating must be in the thickness range of 2 to 40m.4.4 This test method is suitable for most clear anodiccoatings on aluminum articles used in interior or exteriorapplications for decorative or protective purposes.It is appli-cable to coatings that have been dyed if the depth of color is notso great as to obscure the coating-substrate interface.It is alsoapplicable to some transparent organic coatings such as clear ordyed lacquers,provided that their thickness and uniformity fallwithin the guidelines given above.4.5 This test method is not suitable for barrier layer anodiccoatings,integral color coatings except in the lightest colors,hard anodic coatings,or some specialty types of coatings thatare too thin,thick,or rough.Other methods such as theeddy-current technique,Test Method B 244,cross-sectiontechnique,Test Method B 487,and interference microscopetechnique,Test Method B 588,may be applicable to coatingson which the light-section microscope cannot be used.5.Lacquered Anodic Coatings5.1 This test method will not give accurate anodic coating1This test method is under the jurisdiction ofASTM Committee B-8 on Metallicand Inorganic Coatings and is the direct responsibility of Subcommittee B08.10 onGeneral Test Methods.Current edition approved Aug.26,1988.Published November 1988.2Annual Book of ASTM Standards,Vol 02.05.3Available from American National Standards Institute,11 W.42nd St.,13thFloor,New York,NY 10036.1AMERICAN SOCIETY FOR TESTING AND MATERIALS100 Barr Harbor Dr.,West Conshohocken,PA 19428Reprinted from the Annual Book of ASTM Standards.Copyright ASTMNOTICE:This standard has either been superseded and replaced by a new version or discontinued.Contact ASTM International(www.astm.org)for the latest information.thickness measurements on samples that have been lacqueredafter anodizing.5.2 In the case of anodized and