1、Designation: A754/A754M 11 (Reapproved 2016)A754/A754M 18Standard Test Method forCoating Weight (Mass) of Metallic Coatings on Steel byX-Ray Fluorescence1This standard is issued under the fixed designation A754/A754M; the number immediately following the designation indicates the yearof original ado
2、ption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval.A superscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope Scope*1.1 This test method covers the use of X-ray fluorescence (XRF) for
3、determining the coating weight (mass) of metallic coatingson steel sheet. The test method is intended to be used for “on-line” measurements of coating on continuous production lines.1.2 This test method is applicable to the coatings covered by the followingASTM specifications: A463/A463M, A599/A599M
4、,A623, A623M, A653/A653M, A792/A792M, A875/A875M, A879/A879M, A918, A924/A924M, A1046/A1046M, A1063/A1063Mand , and A1063/A1063MA1079. It may be applicable to other coatings, providing that the elemental nature of the coatingand substrate are compatible with the technical aspects of XRF such as the
5、absorption coefficient of the system, primary radiation,fluorescent radiation, type of detection.1.3 This test method includes the procedure for developing a single standard determination of coating weight (mass).1.4 This test method includes procedures for both X-ray tube and isotope coating weight
6、 (mass) measuring instruments.1.5 The values stated in either inch-pound units or SI units are to be regarded separately as standard. Within the text, the SI unitsare shown in brackets. The values stated in each system are not exact equivalents; therefore, each system shall be usedindependently of t
7、he other. Combining values from the two systems may result in nonconformance with the specification.1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety safety,
8、health, and healthenvironmental practices and determine theapplicability of regulatory limitations prior to use.1.7 This international standard was developed in accordance with internationally recognized principles on standardizationestablished in the Decision on Principles for the Development of In
9、ternational Standards, Guides and Recommendations issuedby the World Trade Organization Technical Barriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2A463/A463M Specification for Steel Sheet, Aluminum-Coated, by the Hot-Dip ProcessA599/A599M Specification for Tin Mill Produc
10、ts, Electrolytic Tin-Coated, Cold-Rolled SheetA623 Specification for Tin Mill Products, General RequirementsA623M Specification for Tin Mill Products, General Requirements MetricA653/A653M Specification for Steel Sheet, Zinc-Coated (Galvanized) or Zinc-Iron Alloy-Coated (Galvannealed) by theHot-Dip
11、ProcessA792/A792M Specification for Steel Sheet, 55 % Aluminum-Zinc Alloy-Coated by the Hot-Dip ProcessA875/A875M Specification for Steel Sheet, Zinc-5 % Aluminum Alloy-Coated by the Hot-Dip ProcessA879/A879M Specification for Steel Sheet, Zinc Coated by the Electrolytic Process for Applications Req
12、uiring Designation ofthe Coating Mass on Each SurfaceA902 Terminology Relating to Metallic Coated Steel ProductsA918 Specification for Steel Sheet, Zinc-Nickel Alloy Coated by the Electrolytic Process for Applications RequiringDesignation of the Coating Mass on Each Surface1 This test method is unde
13、r the jurisdiction of ASTM Committee A05 on Metallic-Coated Iron and Steel Products and is the direct responsibility of Subcommittee A05.07on Methods of Testing.Current edition approved May 1, 2016May 1, 2018. Published June 2016May 2018. Originally approved in 1979. Last previous edition approved i
14、n 2011 asA754/A754M 11.A754/A754M 11(2018). DOI: 10.1520/A0754_A0754M-11R16.10.1520/A0754_A0754M-18.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Doc
15、ument Summary page on the ASTM website.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM
16、recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Bo
17、x C700, West Conshohocken, PA 19428-2959. United States1A924/A924M Specification for General Requirements for Steel Sheet, Metallic-Coated by the Hot-Dip ProcessA1046/A1046M Specification for Steel Sheet, Zinc-Aluminum-Magnesium Alloy-Coated by the Hot-Dip ProcessA1063/A1063M Specification for Steel
18、 Sheet, Twin-Roll Cast, Zinc-Coated (Galvanized) by the Hot-Dip ProcessA1079 Specification for Steel Sheet, Complex Phase (CP), Dual Phase (DP) and Transformation Induced Plasticity (TRIP),Zinc-Coated (Galvanized) or Zinc-Iron Alloy-Coated (Galvannealed) by the Hot-Dip Process3. Terminology3.1 Defin
19、itionsFor general definitions of terms relating to metallic-coated steel products, see Terminology A902.3.2 Definitions of Terms Specific to This Standard:3.2.1 averaging time, nthe period over which an electronic measuring instrument acquires samples or “counts” prior to eachupdate of coating weigh
20、t (mass) output; refer to X1.2 for a more detailed explanation.3.2.2 response time, nthe time required for a coating weight (mass) gauge to detect 90 % of a 10 % step change in coatingweight (mass).3.2.3 sample, nthe area of moving sheet that must be measured under standardized conditions to develop
21、 a singledetermination of coating weight (mass).3.2.4 standards, nthe physical standards, either external or internal, that are used to calibrate the measuring instrument.3.2.5 substrate, nthe steel sheet upon which the metallic coating is applied.3.2.6 time constant, nan electronic filtering term,
22、unique to the design of each type of measuring instrument, that defines thetime taken to respond to a step change in coating thickness; refer to X1.3 for a more detailed explanation.3.2.7 X-ray fluorescence, nthe X-rays emitted by an atom when excited to a higher energy state.4. Basic Principle4.1 T
23、he measurement of coating thickness by XRF methods is based on the combined interaction of the coating and substrate,with an intense beam of primary radiation from an X-ray or isotope source. This interaction results in the generation of X-rays ofwell-defined energy. These fluorescent X-rays are det
24、ected by a radiation detector that can discriminate between selected energylevels in the secondary beam.4.1.1 The radiation detector can discriminate between specific fluorescent X-rays because the X-rays generated by theinteraction between the primary beam and the surface being fluoresced have ener
25、gy levels that are unique to each element in thetargeted material. Each element fluoresces at an energy that is characteristic of that element alone. Thus the fluoresced radiationcan be detected separately for either the elements in a coating or the substrate material.4.1.2 The detection system incl
26、udes the radiation detector in conjunction with suitable electronic discriminating circuitry.4.1.3 The thickness of a coating can be determined because a quantitative relationship exists between the intensity of thesecondary radiation captured by the detector and the thickness of the coating materia
27、l. The thickness of a sample can be establishedby comparing the measured intensity and that of a series of standards.4.1.4 The coating weight (mass) can be calculated from the measured coating thickness for a specific coating type. In practice,the electronics are established to report the coating we
28、ight (mass) in commonly used units such as oz/ft2 g/m2.4.2 Measurement Techniques:4.2.1 Two measurement techniques are used. The first technique involves direct measurement of the intensity of the fluorescentX-rays emitted by the coating itself. With this method, the coating weight (mass) is correla
29、ted with the intensity of the fluorescentX-rays emitted by the coating.4.2.2 The second technique involves the measurement of the attenuation of the fluorescent X-rays emitted by the substrate asthey pass through the coating whose weight (mass) is being determined. The correlation in this case is ba
30、sed on the principle thatthe intensity of the X-rays from the fluoresced substrate is a function of the weight (mass) of the coating for a specific coating type.4.2.3 Appendix X2 and Appendix X3 contain a more detailed discussion of these two methods of measuring coating weight(mass).5. Factors Affe
31、cting Accuracy5.1 The equipment used to make a coating weight (mass) measurement using XRF typically consists of a radiation source, adetector, and an electronic system to process the detected signal. The sample absorbs radiation from the source and producesfluorescent radiation. The detector detect
32、s this radiation, and the electronic system converts it into coating weight (mass)information. Since an X-ray measurement is basically an accumulation of random events, the accumulation time must be longenough to produce statistically acceptable data. The precision of a coating weight (mass) measure
33、ment is determined by theequipment and the data collection time. Without a good calibration curve, however, highly precise equipment cannot produce anaccurate result. For example, a very thick coating may produce a very precise X-ray fluorescent signal, but it may be outside therange of the equipmen
34、t. Therefore, the measurement accuracy depends on the equipment, data collection time, and calibration ofA754/A754M 182the instrument. The environment may also influence the measurement accuracy. Since equipment and coating each have uniquecharacteristics, equipment specifications should be reviewed
35、 carefully prior to purchase and installation.5.2 In order to measure coating weight (mass) accurately, the source must have enough strength to produce fluorescent radiationfrom the entire sample volume of interest. The sample volume of interest varies, depending on the XRF method used. When thecoat
36、ing weight (mass) is measured using fluorescence from the coating, the sample volume is the entire layer of the coating. Whenfluorescence from the substrate is used, the sample volume of interest is the lesser of the entire substrate or 5/ ( is the absorptioncoefficient of the substrate for the prim
37、ary beam energy) thickness of the substrate under the coating. The radiated spot size mustbe large enough to cover a sample area as described in the procedure (refer to Table 1). The range of coating weight (mass) forwhich the measuring instrument can be used depends on the strength of the source an
38、d the coating composition. If a coating isthicker than 5/ ( of the coating for the fluorescent beam energy), XRF produced underneath the 5/ thickness cannot emerge fromthe coating due to absorption. A coating thickness of 5/ is defined as the critical thickness. If a coating is very thin, there mayn
39、ot be enough signal from the coating.5.3 The detector must be able to discriminate between signals originating from the coating and the substrate. When the samplecontains elements having similar atomic mass or similar X-ray characteristics, detected signals are difficult to discriminate and themeasu
40、rement accuracy is affected adversely. The measurement accuracy may also be affected adversely when fluorescence fromone element influences fluorescence from another. Equipment capable of measuring XRF from several elements simultaneously,including compensating for variations in coating composition,
41、 is required when the coating composition is unknown (for example,% Zn in Zn-Al or Zn-Ni coating), or the coating contains elements that are present in the substrate (for example, Zn-Fe coatingon Fe), or the coating consists of multiple layers of metal or alloy.5.4 The required data collection time
42、is determined by the strength of the source, sensitivity of the detector, and coating weight(mass). A stronger source and a more sensitive detector typically require a shorter data collection time. The data collection timeshall be long enough to achieve the required precision. For example, if N is t
43、he number of counts detected by a counter in a giventime interval, the inherent error in radiation detection is equal to N.As a guideline, the data collection time should be long enoughto record 10 000 counts for a desired precision of 61 %.5.5 The calibration of the equipment has a very significant
44、 impact on the accuracy of the measurement. The coating compositionof the material to be measured must be similar to that of the calibration standard. If the substrate has any influence on the X-raysignals, then both substrates must be similar. Significant differences in surface roughness and coatin
45、g component segregation mayalso affect the accuracy of the measurement adversely. The coating weight (mass) range of the standards must exceed that of thematerial to be measured and must be within the useful range of the equipment.5.6 Additional precautions are necessary for measurements made on-lin
46、e or in a mill environment.5.6.1 CleanlinessThe measurement instrument window must be kept clean to avoid any interference with the X-ray signal.A film of mill dust containing metal powder is normally more deleterious than that of oil and moisture.5.6.2 StabilityThe equipment should be maintained at
47、 a steady temperature to avoid any instability due to temperature. Theinfluence of variations in air temperature in the gap between the instrument and the material on X-ray measurements must becompensated. The gap between the instrument and the sheet must be uniform and within the specifications of
48、the equipment.Excessive variations in coating weight (mass) readings may be the result of variability in the strip pass-line due to such conditionsas strip off-flatness (for example, wavy edges).5.6.3 Averaging TimeDuring an on-line measurement, the equipment must be operated using an averaging time
49、 suitable fordetecting variations in the coating weight (mass) without affecting measurement accuracy adversely. A very long averaging timewill mask variations in the coating, resulting in a misleading indication of average coating weight (mass). A very short averagingtime will yield unreliable results. (Refer to Table 1 for acceptable combinations.)TABLE 1 Control Variables to Define a Single Data Point (SingleSpot)Variable ValueAType of Gauge X-ray Tube IsotopeArea of fluorescence 1.5 to 5 in.2970 to 3200 mm25 to 14 in.23200 to 9000 mm2Traverse scan s
