ASD-STAN PREN 4729-2015 Aerospace series Trivalent chromium based chemical conversion coatings for aluminium and aluminium alloys (Edition P 1).pdf

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1、ASD-STAN STANDARD NORME ASD-STAN ASD-STAN NORM prEN 4729 Edition P 1 September 2015 PUBLISHED BY THE AEROSPACE AND DEFENCE INDUSTRIES ASSOCIATION OF EUROPE - STANDARDIZATION Rue Montoyer 10 - 1000 Brussels - Tel. 32 2 775 8126 - Fax. 32 2 775 8131 - www.asd-stan.org ICS: Descriptors: ENGLISH VERSION

2、 Aerospace series Trivalent chromium based chemical conversion coatings for aluminium and aluminium alloys Srie arospatiale Conversion chimique au chrome trivalent de laluminium et des alliages daluminium Luft- und Raumfahrt Chrom-(III)-basierte chemische Konversionsberzge fr Aluminium und Aluminium

3、legierungen This “Aerospace Series“ Prestandard has been drawn up under the responsibility of ASD-STAN (The AeroSpace and Defence Industries Association of Europe - Standardization). It is published for the needs of the European Aerospace Industry. It has been technically approved by the experts of

4、the concerned Domain following member comments. Subsequent to the publication of this Prestandard, the technical content shall not be changed to an extent that interchangeability is affected, physically or functionally, without re-identification of the standard. After examination and review by users

5、 and formal agreement of ASD-STAN, it will be submitted as a draft European Standard (prEN) to CEN (European Committee for Standardization) for formal vote and transformation to full European Standard (EN). The CEN national members have then to implement the EN at national level by giving the EN the

6、 status of a national standard and by withdrawing any national standards conflicting with the EN. Edition approved for publication 1st September 2015 Comments should be sent within six months after the date of publication to ASD-STAN Metallic Material Domain Copyright 2015 by ASD-STAN prEN 4729:2015

7、 (E) 2 Contents Page Foreword 2 1 Scope 3 2 Purpose of process . 3 3 Normative references 3 4 Terms and definitions . 3 5 Applicability and limitations of the process . 4 6 Classification 4 7 Requirements . 4 8 Main technical engineering requirements . 7 9 Quality requirements . 8 10 Quality assuran

8、ce 10 11 Health, safety and environmental aspects 11 12 Designation 11 Foreword This standard was reviewed by the Domain Technical Coordinator of ASD-STANs Metallic Material Domain. After inquiries and votes carried out in accordance with the rules of ASD-STAN defined in ASD-STANs General Process Ma

9、nual, this standard has received approval for Publication. prEN 4729:2015 (E) 3 1 Scope This standard specifies trivalent chromium based chemical conversion coatings for aluminium and aluminium alloys. It covers the application by bath but also by touch-up. It doesnt give complete in-house process i

10、nstructions; these shall be given in the manufacturers detailed process instructions. 2 Purpose of process The aim of the trivalent chromium based chemical conversion coatings is to increase corrosion resistance, to improve the adhesion of paints and varnishes and to ensure electrical conductivity.

11、Coatings are also suitable for the repair of mechanically damaged anodic coatings. 3 Normative references The following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For und

12、ated references, the latest edition of the referenced document (including any amendments) applies. EN 4707, Aerospace series Acid pickling of aluminum and aluminum alloy without hexavalent chromium 1) EN 9100, Aerospace series Quality Management Systems Requirements for Aviation, Space and Defence O

13、rganizations EN ISO 2409, Paints and varnishes Cross-cut test EN ISO 2812-2, Paints and varnishes Determination of resistance to liquids Part 2: Water immersion method EN ISO 3892, Conversion coatings on metallic materials Determination of coating mass per unit area Gravimetric methods EN ISO 9227,

14、Corrosion tests in artificial atmospheres Salt spray tests 4 Terms and definitions For the purposes of this document, the following terms and definitions apply. 4.1 batch unless otherwise specified, it comprises parts of the same type (shape, size, material), processed at the same time in the same b

15、ath 4.2 substrate material upon which a coating is directly deposited, in the case of a single or first coating, the substrate is the basis metal and for a subsequent coating, the intermediate coating is the substrate 1) Published as ASD-STAN Prestandard at the date of publication of this standard.

16、http:/www.asd-stan.org/ prEN 4729:2015 (E) 4 4.3 pit substrate corrosion defect at which the conversion coating is penetrated Note 1 to entry: Typical characteristics of corrosion pits are: rounded or irregular or elongated geometry, comet tail or line or halo that emerges from the cavity, some corr

17、osion by-products inside pits (on aluminium test samples the by-product may be granular, powdery or amorphous and white, grey or black in colour). Note 2 to entry: To be considered a corrosion pit, a surface cavity must exhibit at least two of the above characteristics. 5 Applicability and limitatio

18、ns of the process This standard applies whenever referenced. Parts with features that may trap treatment solutions shall be subjected to additional rinsing operations to ensure removal of treatment solutions. Chemical conversion treatment shall not be applied if removal of treatment solution cannot

19、be assured. Chemical conversion coatings shall not be applied to parts before bonding or welding. The maximum in service temperature of the chemical conversion coatings, is 100 C. 6 Classification 6.1 Coating weight For trivalent chromium base conversion coating, the mass per unit area should be ran

20、ged from 0,2 g/m2 to 0,9 g/m2. 6.2 Materials Category 1: Aluminium alloy 1 000, 5 000 and 6 000 series, Category 2: Aluminium alloy 2 000 and 7 000 series, Category 3: Aluminium alloy castings. For cladded aluminium alloys, the clad is considered as the material. 7 Requirements 7.1 Process requireme

21、nts 7.1.1 Information for the processor categories of materials; substrate standard reference and heat treatment; areas to be coated; specification for testing on parts and/or samples; criticality of parts. prEN 4729:2015 (E) 5 7.1.2 Condition of parts prior to processing welding, soldering/brazing,

22、 mechanical operations and heat treatments shall have been completed. the parts shall be free of oil, grease, marking inks and other surface contaminations; mechanically disturbed layer shall be removed either by mechanical or chemical processes; in case of re-treatment all residuals from the previo

23、us coating shall be completely removed. Tooling The tools and metal masking tooling must be protected against corrosion, and/or free of corrosion or any other damage which may be detrimental to the treatment during use. The part racks and tools must be designed and set up in such a manner as to: avo

24、id any retention of air or treatment solution in the parts, facilitate neutralization and removal of solutions during rinsing operations, avoid the treatment any accidental contact between the parts to be treated and the tank equipments, and between the different parts. The parts shall be previously

25、 degreased prior to masking. Component areas which must not be coated shall be masked with suitable material. 7.1.3 Pre-treatment The pre-treatment phase shall not result in critical deterioration of dimensions, surface finish and mechanical properties of parts. For conversion coating apply by touch

26、 up process or following vapor deposited aluminium (IVD or PVD) a mechanical pre-treatment is allowed. Cleaning Surface preparation means any method able to completely eliminate all surface contaminations. Pickling It shall not cause pitting, intergranular corrosion or any alterations to the metallu

27、rgical characteristics or mechanical strength of the material. Chemical conversion coating must be performed immediately after pickling (in accordance with aluminium and aluminium alloys pickling standard EN 4707). Rinsing bath See 7.1.4. prEN 4729:2015 (E) 6 7.1.4 Rinsings The parts shall be rinsed

28、 thoroughly, it is recommended that the final rinsing of each step of overall process has to be carried out in deionized water. The supplied deionised water shall comply with the following requirements: pH value at 25 C: 5,0 to 8,0 total residue mg/l: 5 conductivity S/cm: 20 For touch-up application

29、, rinsing is optional, according to product specification. 7.1.5 Treatment The parts are submerged in a still or agitated bath or treated by spraying or by touch-up (RTU, gel, stick) . A commercial product may be used according to the manufacturers instructions. During the bath application process:

30、distance between parts shall be adapted in order to avoid shocks. parts shall be fully immersed, in such a way that all air can escape. during emersion the bath fluid shall run off from all areas and cavities. tubes shall be placed in the bath in such a way that the bath fluid can rise in the bath,

31、expelling all the air. If not, the bath fluid shall then be drawn in or pump through. the process shall be performed such, that parts do not dry between single process steps (pre-treatment, treatment, post-treatment). the parameters (temperature, time) shall be adapted to the material and its requir

32、ements in accordance with manufacturer instructions. It is recommended to handle the parts after treatment and after each post-treatment step with gloves. a rinsing step shall be performed according 7.1.4. parts shall be stored under clean and dry conditions. Drying may be carried out with dry, oil-

33、free air at ambient temperature or at max. 60 C. 7.1.6 Post-treatment Optional chemical treatment to improve corrosion resistance performance In case of optional chemical treatments the drying shall not be applied. A commercial product may be used according to the manufacturers instructions. See 7.1

34、.5 for process recommendation. prEN 4729:2015 (E) 7 Paints or varnishes It is recommended to apply the primer or the varnish coat 48 h maximum after treatment or according to specific purchaser requirement. In case of over lead time an appropriate storage and visual inspection (homogeneous appearanc

35、e and free from pitting, stains and contamination) should be carried out after the conversion coating process. In case of heterogeneous aspect, pitting, stains and contamination reprocessing of parts depends on the material and may only be carried out following confirmation and requirements by the m

36、anufacturer. 7.1.7 Removal of the coating The stripping shall be carried out following confirmation and requirements between manufacturer and purchaser. The stripping variants used shall not deteriorate the dimensions, surface finish and mechanical properties of parts, either by using a nitric acid

37、solution at ambient temperature or mechanically by light abrasion. 8 Main technical engineering requirements 8.1 General The final coating is expected to meet the following main requirements: homogenous appearance of the coating; a good adhesion of coating to the substrate, and paint systems to the

38、coating (according EN ISO 2409); coating weight according to required range (see EN ISO 3892), the test specimen must be dried at room temperature with clean compressed air and coating weight measurement must be done within three (3) hours after treatment; corrosion protection (according EN ISO 9227

39、); electrical conductivity (optional test, under agreement between purchaser and supplier). 8.2 Appearance It shall be uniform and free from defects. Powdery coatings are not acceptable. Differences in colour are permissible, due to: materials category (see 6.2), commercial product used for coating.

40、 8.3 Coating weight See Clause 6. According to EN ISO 3892. prEN 4729:2015 (E) 8 8.4 Corrosion resistance After testing, a maximum of five pits is permissible per test specimen (surface 1 dm2) and the diameter of each point shall not exceed 0,8 mm. The inspection shall not be carried out at less tha

41、n 6 mm from: the test specimen edges, the marking, the mounting points. Coated test pieces shall be: aged for at least 24 h at ambient temperature in a maximum range of 10 days; exposed to a continuous neutral salt spray test according to EN ISO 9227-NSS, see Table 1. Table 1 Minimum NSS exposure (a

42、ccording to 8.4) Conversion coating (h) with or without optional post-treatment (under agreement between customer and purchaser) Category 1 168 Category 2 72 Category 3 Under agreement between customer and purchaser (except AS7G06: 168 h) rinsed in deionized water,(see 7.1.4) to remove sodium chlori

43、de residues; air dried. Inspection shall be made with naked eyes. 8.5 Adhesion Apply an adhesive tape (scotch tape 3M 250 or 3M 2525 or equivalent according EN ISO 2409). A visual inspection shall not show any pulling off of the coating at the surface of the substrate or conversion coating. Concerni

44、ng paint adhesion on the conversion coating: test by scribe and adhesive tape according EN ISO 2409 and EN ISO 2812-2 (at initial stage and after immersion 14 days in water), a visual inspection shall not show any pulling off of the organic coating or other lack of adhesion to the conversion coating

45、. Accepted grade before and after immersion: 1. 8.6 Electrical contact resistance Under agreement between customer and purchaser. 9 Quality requirements 9.1 Approval of the processor See EN 9100. prEN 4729:2015 (E) 9 9.2 Process approval The processor shall carry out: the conversion coating on pre-p

46、roduction parts and/or samples determined by agreement between the processor and the purchaser; the tests specified in this standard, unless otherwise agreed between the processor and the purchaser. The process chart defined in the manufacturers process instructions shall not be changed without any

47、previous agreement from the purchaser. 9.3 General points During all the process operations, the operating conditions must be within the parameters defined in the manufacturers detailed process instructions. Regular controls must be performed on the facilities and the products used and on conformanc

48、e of the application process conditions to the requirements of this document and of the manufacturers detailed process instructions. All records of process parameters, tests and inspection results shall be registered under the control of the quality assurance of the workshop. All process operators s

49、hall be adequately trained. In order to verify the above specified design requirements and maintain the process with appropriate performances, the process needs to be checked by: periodic tests on samples coated under the same conditions as the parts, periodic bathes chemical analysis, parts acceptance controls. The minimum tests and controls are defined in the