1、BRITISH STANDARD AEROSPACE SERIES BS M 93:2005 Protection of magnesium-rich alloys against corrosion Specification ICS 49.025.15; 49.040 BS M 93:2005 This British Standard was published under the authority of the Standards Policy and Strategy Committee on 22 March 2005 BSI 22 March 2005 The followin
2、g BSI references relate to the work on this British Standard: Committee reference ACE/65 Draft for comment 02/709330 DC ISNB 0 580 45462 2 Committees responsible for this British Standard The preparation of this British Standard was entrusted to Technical Committee ACE/65, Inspection and testing req
3、uirements for non-metallic materials, upon which the following bodies were represented: British Hydromechanics Research Group British Plastics Federation Society of British Aerospace Companies Ltd. Amendments issued since publication Amd. No. Date CommentsBS M 93:2005 BSI 22 March 2005 i Contents Pa
4、ge Committees responsible Inside front cover Foreword ii 1S c o p e 1 2 Normative references 1 3T e r m s a n d d e f i n i t i o n s 1 4 Classification 1 5 Information to be supplied to the processor 1 6 Condition of parts prior to processing 2 7 Process schedule 2 8I n s p e c t i o n 3 9 Removal
5、of coatings 3 10 Quality assurance 3 Annex A (informative) Cleaning and pickling 4 Annex B (normative) Chromating 6 Annex C (normative) Anodizing 8BS M 93:2005 ii BSI 22 March 2005 Foreword This British Standard has been prepared by Technical Committee ACE/65 and is one of a series for paints and va
6、rnishes suitable for aerospace purposes. It has been assumed in the drafting of this standard that the execution of its provisions is entrusted to appropriately qualified and experienced people. WARNING This British Standard calls for the use of substances and/or procedures that may be injurious to
7、health if adequate precautions are not taken. It refers only to technical suitability and does not absolve the user from legal obligations relating to health and safety at any stage. This publication does not purport to include all the necessary provisions of a contract. Users are responsible for it
8、s correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages 1 to 9 and a back cover. The BSI copyright notice displayed in this document indic
9、ates when the document was last issued.BS M 93:2005 BSI 22 March 2005 1 Introduction Magnesium and its alloys are susceptible to corrosion and, as such, require corrosion protection. The protective systems involve either chromating or anodizing as a pre-treatment. Chromating is a chemical conversion
10、 process producing very thin (typically 2 .5 10 p34m to 1 4m) coatings that provide a good surface on which to paint and a supply of inhibiting hexavalent chromate ions. Anodizing, by definition, is an electrolytic process producing thicker (13 4m p 40 4m) but inherently porous coatings. These coati
11、ngs have to be sealed with a heat-cured coating and might or might not have a finish coat. 1 Scope This British Standard specifies the methods of protection for magnesium and magnesium alloys and specifies the required characteristics for the performance of various protection schemes for magnesium,
12、as well as the quality assurance of the coating obtained. Two types of protection are produced: a) Type I: Chromating and BS X 38 primer and finish coat; b) Type II: Anodizing and unpigmented BS X 38 sealer and finish coat (optional) This standard applies to parts in magnesium and magnesium alloys w
13、hen used in aerospace construction, when reference is made to this standard. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the refer
14、enced document (including any amendments) applies. BS 2015, Glossary of paint and related terms. BS EN 2437, Aerospace series Chromate conversion coatings (yellow) for aluminium and aluminium alloys. BS X 38, Heat curing paint for aerospace purposes Specification. 3 Terms and definitions For the pur
15、poses of this British Standard, the terms and definitions given in BS 2015 apply. 4 Classification Two types of protection shall be classified as follows. a) Type I: Chromating and BS X 38 primer and finish coat. b) Type II: Anodizing and unpigmented BS X 38 sealer and finish coat (optional). 5 Info
16、rmation to be supplied to the processor The following information shall be supplied to the processor of the parts: a) classification (see Clause 4); b) magnesium alloy being processed; c) areas to be processed; d) thickness measuring points (Type II only); e) electrical contact points or where these
17、 are prohibited (Type II only); f) surface roughness requirements of the finished part; g) requirements for any finishing operations, i.e. painting, etc.BS M 93:2005 2 BSI 22 March 2005 6 Condition of parts prior to processing Unless otherwise specified, all heat treatments, brazing and welding trea
18、tments and forming operations shall be completed prior to processing. The surface shall be free from cracks and other metallurgical defects. 7 Process schedule 7.1 Processing The processing specified in 7.2 shall be followed unless otherwise agreed with the purchaser. 7.2 Pre-treatment 7.2.1 Preclea
19、ning The cleaning method shall be appropriate for the contamination experienced on the materials. NOTE Solvent degreasing followed by cleaning in an alkaline solution is generally the most effective method. Annex A details an example of a recognized process. 7.2.2 Pickling/oxide removal A pickling o
20、peration shall remove natural oxides in order to obtain a fresh surface ready for conversation to the chromate or anodic coating. It shall not degrade the metallurgical properties or fatigue behaviour of the material nor initiate pitting. It shall not change the dimensional tolerances or surface rou
21、ghness beyond that which is specified. Machined areas need not undergo the pickling operation. NOTE Acceptable pickling methods can be found in Annex A. 7.2.3 Rinsing Rinsing shall be performed by immersion in clean running water/spray followed by immersion in hot deionized or distilled water, minim
22、um temperature 80 C, and finally using dry compressed air to ensure that all entrapment areas are clear. If parts are to be further treated in aqueous solutions, then the drying procedure may be omitted provided that the time elapsed between operations is insufficient to cause the part to dry out or
23、 corrode. 7.3 Treatment 7.3.1 General After pre-treatment, one of the treatments specified in 7.3.2 (Type I) or 7.3.3 (Type II) shall be carried out. 7.3.2 Type I Chromating Chromate treatment shall be carried out by one of the methods described in Annex B. Chromated parts, where the chromate film i
24、s intended to form part of the final protection scheme, shall be coated with a primer conforming to BS X 38 within 16 h of chromating. 7.3.3 Type II Anodizing Anodizing shall be carried out by one of the methods described in Annex C. Anodizing shall not be carried out on parts that have been chromat
25、ed or surface sealed. All anodized areas shall be sealed as soon as possible, and no longer than eight hours after anodizing, with an unpigmented sealer coating conforming to BS X 38. 7.4 Post-treatment 7.4.1 Type I Chromate coatings Where painting with a finish coat is specified, it shall be applie
26、d within 16 h after the application of the BS X 38 primer coating. 7.4.2 Type II Anodized coatings Where painting with a finish coat is specified, it shall be applied within 16 h after the application of the BS X 38 sealer coating.BS M 93:2005 BSI 22 March 2005 3 8 Inspection 8.1 Where it is not pra
27、ctical to perform the quality control on processed parts, test pieces that are representative of a part, or of a batch of parts, which have been processed the same way and at the same time shall be used. 8.2 The quality assurance authority shall specify the number of parts to be inspected per batch
28、or parts to be subjected to individual inspection. All parts shall be visually inspected to ensure conformity to the specified requirements. 9 Removal of coatings 9.1 Type I Chromate coatings Where the coating, produced by any of the processes in Annex B, fails to meet the required acceptance standa
29、rd or needs to be re-chromated after storage then the part shall be stripped, unless requiring machining back, using the process detailed in Annex B, B.4. 9.2 Type II Anodized coatings Where the coating, produced by any of the processes in Annex C, is sub-standard or fails to meet the required accep
30、tance standard then the part may be stripped using a process detailed in Annex C. However, when re-anodizing, the dimensional and surface roughness shall conform to the values specified. 10 Quality assurance 10.1 Qualification of the process When process qualification is required by the purchaser, s
31、ample parts and/or panels shall be prepared for approval by the purchaser before production commences. Qualification items shall be processed according to an identified process schedule and the items shall be tested for conformity with the qualification requirements. No deviation shall be permitted
32、from the process schedule without prior approval of the purchaser. 10.2 Acceptance requirements See Annex B and Annex C. 10.3 Rework procedure 10.3.1 Type I Chromate films Where it is necessary to repair chromate films that have been damaged locally, the exposed metal shall be lightly swabbed with a
33、n acid chromate solution approved to BS EN 2437. This method shall not be used over areas greater than 10 cm 2or on assemblies where there is a danger of entrapment of treatment chemicals. In such cases, the component shall be stripped (B.4). 10.3.2 Type II Anodized coatings There is no method for t
34、he repair of anodized coatings; these coatings shall be completely stripped and recoated. See 9.2. 10.4 Information to be provided by the processor The following information shall be provided by the processor: a) reference to this standard, i.e. BS M 93; b) type; c) date of processing; d) batch numb
35、er; e) re-work (if carried out).BS M 93:2005 4 BSI 22 March 2005 Annex A (informative) Cleaning and pickling NOTE Although this method contains requirements, it is informative as noted in 7.2. A.1 Degreasing A.1.1 Organic solvent degreasing The following may be used for organic solvent degreasing: a
36、) hot solvents, non-water washable. Halogenated hydrocarbons in the liquid or vapour phase, such as trichloroethylene or perchloroethylene; b) cold solvents, non-water washable. Solvents in the liquid phase, such as those listed under a) and white spirit. It can be applied by immersion, spraying or
37、manually. When the parts are degreased by immersion in the above solvents, at least three successive immersions shall be applied. When the solvent is contaminated by, for instance, grease, it shall be replaced. A.1.2 Aqueous degreasing A mild aqueous alkaline cleaner may be used, alone or in additio
38、n to preliminary solvent degreasing. They may be used hot or cold, with or without electrical current. Alkaline cleaners containing more than 2 % sodium hydroxide will etch some magnesium alloys. After aqueous cleaning, the parts shall be thoroughly rinsed as per 7.2.3. A.2 Pickling/oxide removal A.
39、2.1 General Use one of the methods of pickling/oxide removal in A.2.2 and A.2.3. A.2.2 Fluoride anodizing (method 1) A.2.2.1 General This process is intended preferably to follow abrasive blasting in the cleaning procedure for magnesium alloy castings, when it will substantially restore the corrosio
40、n resistance lost as a result of abrasive blasting. The process can be applied to all magnesium alloys in all forms. A.2.2.2 Composition of solution The solution shall consist of a solution in water having the following composition: ammonium bifluoride (NH 4 .HF 2 ) 150 to 250 g/l. The solution may
41、be contained in a vessel lined with hard rubber or suitable plastic material resistant to acid fluoride solution. The inner wall of the vessel shall not conduct electricity. A.2.2.3 Operation of solution Do not let the temperature of the solution exceed 40 C. Stir the solution before use and prefera
42、bly agitate it gently during the process. Normally, treat parts in pairs of approximately equal surface area using alternating current. Fix the parts in good electrical contact and suspend them not less than 250 mm below the surface of the solution. All parts of the fixing clamps that extend into th
43、e solution shall be made of magnesium alloy other than magnesium-manganese alloy. Apply alternating current and raise the voltage to 90 V to 120 V. NOTE Current flow is usually heavy at first, but diminishes rapidly as surface impurities are removed and an unbroken magnesium fluoride film is formed.
44、 Continue the treatment for 10 min to 15 min or until the current density falls to below 50 A/m 2 . Switch the current off and remove the parts from the solution. Wash, rinse (see 7.3.3) and examine them. WARNING Because of the high voltage used, access to the solution shall be prevented while the c
45、urrent is switched on. Spray from the solution is poisonous, and suitable ventilation shall be provided.BS M 93:2005 BSI 22 March 2005 5 A.2.2.4 Control of solution composition Maintain the composition of the solution between 150 g/l and 250 g/l ammonium bifluroide by the addition of fresh quantitie
46、s of this salt. Discard the solution if it has become excessively contaminated with foreign metals, acid radicals other than fluoride or organic matter, indicated by failure of the solution to perform as described above and/or the failure to develop an acceptable film as described in A.2.2.5. Confir
47、m satisfactory performance by processing test coupons of a suitable magnesium alloy, either immediately before the parts to be anodized or, where the solution is in at least daily use, at intervals of not less than one week. A.2.2.5 Requirements for acceptance The parts shall have a uniform clean wh
48、ite or pearly grey appearance and be free from foundry sand. NOTE Dark areas in hollows may indicate entrapment of gas during treatment. Very thin semi-transparent, films indicate treatment at too low a voltage; only on machined surfaces or on wrought surfaces in good condition is such a film accept
49、able. An etched appearance indicates a solution too low in ammonium fluoride, too hot, or operated at too high a voltage. A thick film can indicate the presence of acid radicals other than fluoride. Surface pitting can be caused by chloride in the solution. A.2.2.6 Fluoride film removal Remove the fluoride film by one of the following methods as appropriate. a) immersion in 50 ml/l to 100 ml/l nitric acid (SG1.42) solution at room temperature; NOTE This method will result in so
