1、Magnesium Alloy, Processes for Pretreatment andPrevention of Corrosion onNOTICEThis document has been taken directly from U.S. Military Specification MIL-M-3171C, Amendment 1, and contains only minor editorial and format changes required to bring it into conformance with the publishing requirements
2、of SAE technical standards. The initial release of this document is intended to replace MIL-M-3171C, Amendment 1. Any part numbers established by the original specification remain unchanged.The original Military Specification was adopted as an SAE standard under the provisions of the SAE Technical S
3、tandards Board (TSB) Rules and Regulations (TSB 001) pertaining to accelerated adoption of government specifications and standards. TSB rules provide for (a) the publication of portions of unrevised government specifications and standards without consensus voting at the SAE Committee level, and (b)
4、the use of the existing government specification or standard format.Any material relating to qualified product lists has not been adopted by SAE. This material was part of the original military specification and is reprinted here for historic reference only.AEROSPACE MATERIAL SPECIFICATIONAMS-M-3171
5、Issued 1998-04 Reaffirmed 2011-04 SAE Technical Standards Board Rules provide that: “This report is published by SAE to advance the state of technical and engineering sciences. The use of this report is entirely voluntary, and its applicability and suitability for any particular use, including any p
6、atent infringement arising therefrom, is the sole responsibility of the user.” SAE reviews each technical report at least every five years at which time it may be reaffirmed, revised, or cancelled. SAE invites your written comments and suggestions. Copyright 2011 SAE International All rights reserve
7、d. No part of this publication may be reproduced, stored in a retrieval system or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of SAE. TO PLACE A DOCUMENT ORDER: Tel: 877-606-7323 (inside USA and Canada)
8、 Tel: +1 724-776-4970 (outside USA) Fax: 724-776-0790 Email: CustomerServicesae.org SAE WEB ADDRESS: http:/www.sae.org SAE values your input. To provide feedback on this Technical Report, please visit http:/www.sae.org/technical/standards/AMSM3171 AMS-M-3171 SAE AMS-M-3171- 2 -1. SCOPE:1.1 Scope: Th
9、is specification covers general requirements for the apparatus, material, and procedures to be used in the processing of magnesium base alloys for the purpose of increasing their corrosion resistance and by producing surfaces suitable for organic paint finish systems.1.2 Classification: 1.2.1 Types
10、- The magnesium corrosion preventive treatments shall be of the following types:Type I - Chrome Pickle TreatmentType III - Dichromate TreatmentType IV - Galvanic Anodizing TreatmentType VI - Chrome Acid Brush-on TreatmentType VII- Fluoride Anodizing Process plus Corrosion Preventive TreatmentType VI
11、II- Chromate Treatment2. APPLICABLE DOCUMENTS: The following publications, of the issues in effect on date of invitation for bids or request for proposal, form a part of this specification to the extent specified herein.2.1 U.S. Government Publications: Available from DODSSP, Subscription Services D
12、esk, Building 4D, 700 Robbins Avenue, Philadelphia, PA 19111-5094.MIL-C-46079 Coating, Epoxy, Baking Type for Magnesium CastingMIL-STD-105 Sampling Procedures and Tables for Inspection by Attributes3. REQUIREMENTS: 3.1 General requirements: 3.1.1 Materials: All materials used in the cleaning or trea
13、ting of magnesium base alloys shall be of good quality and suitable for the purpose intended. All chemicals used in cleaning and treating shall be free from metallic impurities such as salts of heavy metals (lead, nickel, zinc, arsenic, antimony, etc.).3.1.2 Workmanship: The treatments covered by th
14、is specification shall be controlled and operated to give a uniform surface conforming to the requirements specified herein. The surface shall be free from breaks, discontinuities, scratches, and other damage. The size and number of contact marks shall be held at a minimum.AMS-M-3171 SAE AMS-M-3171-
15、 3 -3.2 Cleaning and pickling operations (see 3.12): 3.2.1 Solvent cleaning: Grease or oil shall be removed by means of vapor degreasing, ultrasonic cleaning, organic solvents, or by emulsion cleaning which employs a mineral oil distillate and an emulsifying agent. For this cleaning operation, chlor
16、inated solvents, petroleum spirits, naphtha, lacquer thinners, and similar grease solvents which do not attack magnesium may be used. Methyl or wood alcohol (CH3OH), is specifically prohibited as a solvent cleaner for magnesium alloys.3.2.2 Mechanical cleaning: Mechanical cleaning shall consist of s
17、and, shot, grit, or vapor blasting, sanding, hard bristle brushing, grinding and rough polishing. When sand, shot, or grit blasting methods are employed, there is danger of surface contamination which will greatly increase the initial corrosion rate of magnesium. In such case, subsequent pickling op
18、erations, as specified in 3.2.4.2, or fluoride anodizing as specified in 3.9.1 shall be employed.3.2.2.1 New sand castings: New sand castings shall be sand or grit blasted and then pickled in conformance with 3.2.4.2 or fluoride anodized as specified in 3.9.1.3.2.2.2 Discolored or corroded castings:
19、 Discoloration or corrosion products shall be removed from rough unmachined castings. This operation may be performed by blasting and subsequent pickling as specified in 3.2.4.2. Machine parts or sections, which may be held to close dimensional tolerances, may be cleaned by use of a chromic acid pic
20、kle solution conforming to 3.4.1.3.2.2.3 Welding flux: When using flux in the welding operations, the welded sections shall be thoroughly cleaned immediately after the operation to remove all traces of flux. Where possible, hot water and a hard bristle brush shall be used to insure thorough flux rem
21、oval. Inaccessible welded sections shall be washed with a high velocity stream of water (preferably hot). They shall then be immersed for 1 hour in a 2 to 5 percent sodium dichromate solution maintained at 180 to 212 F. The parts shall be thoroughly rinsed in cold running water.3.2.3 Alkaline cleani
22、ng: Cleaning prior to application of treatments other than Type I when used for protection during shipment or storage, shall be done by cleaning the parts in an alkaline cleaner recommended for steel or in cleaning solution as specified in 3.3.2. Any alkaline cleaner used shall have a pH that is mai
23、ntained above 8. Alkaline cleaning, prior to application of Type I when used for protection during shipment or storage only, may be omitted provided the parts are free from grease, oil, or other deleterious deposits at the time of application. Alkaline cleaners containing more than 2 percent caustic
24、, such as sodium hydroxide will etch ZK60A, ZK60B, and some magnesium-lithium alloys with resultant decrease in dimensions. If such a dimensional change is not desirable, the alkaline cleaners used on these alloys should not contain more than 2 percent caustic.AMS-M-3171 SAE AMS-M-3171- 4 -3.2.3.1 G
25、raphite lubricant removal: Graphite base lubricants shall be removed from hot formed magnesium sheet parts by soaking the parts for 10 to 20 minutes in an aqueous sodium hydroxide (NaOH) bath containing 13 oz/gallon of NaOH and maintained at 190 to 212 F. This bath shall be maintained at a pH above
26、13. One-tenth ounce per gallon of soap or wetting agent may be added to this solution if removal of heavy films of mineral oil is required. The parts shall be thoroughly rinsed in cold water and immersed in a chromic-nitrate pickle as specified in 3.4.2 for approximately 3 minutes. If complete clean
27、ing is not obtained the first time, this operation shall be repeated until the parts are clean. Because of the difficulty of removing graphite from chrome pickled sheet, such sheet shall not be used for forming unless the chrome pickle coating has been completely removed as specified in 3.2.3.2.3.2.
28、3.2 Previously applied chemical finishes: Previously applied chemical finishes shall be removed. Magnesium base alloys sometimes are furnished with Type I treatment which provides protection during shipment, storage, and machining. The coating resulting from Type I treatment remaining on the unmachi
29、ned areas will impair the film produced by Type III and Type IV treatments and consequently, must be removed. This operation may be performed by use of alkaline cleaners such as the types specified in 3.2.3. If the finish is difficult to remove, the part should be immersed in the chromic acid pickle
30、 specified in 3.4.1. Alternate immersion in the alkaline cleaner and chromic acid pickle may be necessary to remove very old finishes.3.2.3.2.1 The Type VI treatment may be applied over previously applied thin film by Type I or Type VI treatments without removing these finishes (see 3.8.1).3.2.4 Aci
31、d pickling: 3.2.4.1 General pickling: General pickling to remove oxide layers, old chemical finishes, burned-on drawing and forming lubricants, and other water insoluble or non-emulsifiable substances shall be accomplished, preferably by using a chromic acid type pickle conforming to 3.4.1 or 3.4.2.
32、3.2.4.2 Pickling of magnesium sand and permanent mold castings: Magnesium sand and permanent mold castings which have been subjected to blasting operations shall be pickled in a sulfuric acid pickle conforming to 3.4.3 or in a sulfuric-nitric acid pickle conforming to 3.4.4. Pickling operations shal
33、l be continued until 0.002 inch of surface has been removed, whenever dimensional tolerances permit.3.2.4.3 Pickling of magnesium sheet and plate: Magnesium sheet and plate up through 0.500 inch thick shall have the mill scale removed to insure a clean surface to which subsequent treatment will be a
34、pplied. Where dimensional tolerances permit, 0.0005 inch to 0.001 of metal surface shall be removed. An acetic-nitrate pickle conforming to 3.4.7 or equivalent acid pickle shall be used for this operation.3.2.4.4 Pickling of magnesium die castings: Die castings that are to be pickled for maximum cor
35、rosion resistance and a more uniform surface for treating shall be pickled in a chromic-nitric HF pickle conforming to 3.4.5 or a phosphoric acid pickle conforming to 3.4.6.AMS-M-3171 SAE AMS-M-3171- 5 -3.2.5 Retreatment of wrought and cast parts: 3.2.5.1 Grease and oil: Grease and oil shall be remo
36、ved in conformance with 3.2.1.3.2.5.2 Paint: Old paint coatings shall be removed, preferably by the use of an alkaline (caustic) liquid paint remover. Solvent type paint removers may be used provided the operation is followed by a wash with a wax-free solvent to remove any wax which may have been le
37、ft on the surface. Light blasting may be used to remove paint from parts of substantial thickness, but only sanding shall be permitted on thin sheets. If sand-blasted, the part shall be pickled in conformance with 3.2.4.2.3.2.5.2 Chemical finishes: Chemical finishes shall be removed as specified in
38、3.2.3.2 before retreatment.3.2.5.3 Alkaline cleaning: Parts to be retreated shall be cleaned in an alkaline cleaning solution as specified in 3.2.3.3.2.5.5 Corrosion or oxide films: Corrosion products or oxide films shall be removed, preferably by use of the chromic acid pickle or chromic-nitrate pi
39、ckle as specified in 3.4.1 and 3.4.2, respectively.3.3 Alkaline cleaning solutions: 3.3.1 Alkaline cleaning as required in 3.2.3 may be performed by using proprietary type cleaners, in which case the operation shall be as specified by the vendor. In no case will any such cleaner be used that has a p
40、H lower than 8. An alkaline cleaner of the formulation given in Table I may be used quite satisfactorily. The parts are simply immersed in the solution, or, if direct current is available, the parts are made cathodes in the bath and a current density of 10 to 40 amp/sq. ft. at 6 volts, is applied. W
41、hen cathodic cleaning is employed, the time required for adequate cleaning is reduced. Parts are given a thorough rinse in cold running water after alkaline cleaning. Parts shall be cleaned until no water breaks occurs in the rinse.3.3.2 Anodic cleaning employing the work as the anode in the alkalin
42、e cleaning solution is generally not recommended because of the formation of undesirable oxide films as well as pitting of magnesium alloy surfaces from prolonged contact.TABLE IALKALINE CLEANER SOLUTION AND OPERATIONCompositionOunces per gallon(water added tomake one gallon)OperatingtemperatureFTre
43、atmenttime-minutesTankconstruc-tionSodium hydroxide (NaOH) 8 190 to 212 3 to 10 SteelTrisodium phosphate(Na3PO4 12H2O) 1-1/3Soluble soap or wettingagent 0.1AMS-M-3171 SAE AMS-M-3171- 6 -3.4 Acid pickling solutions: 3.4.1 Chromic acid pickle: Chromic acid pickling may be used where parts with close t
44、olerance limits are to be finished since this pickle causes no dimensional change. It can be used in removing old chemical finishes by alternate immersion in an alkaline cleaner specified in 3.3.2 and the chromic acid pickle. This pickle is satisfactory for removal of surface oxidation, corrosion pr
45、oducts, and for general cleaning of parts. It is not satisfactory for the removal of sand or the effects of blasting and shall not be used for parts containing copper based inserts unless masked off. Excessive amounts of anions, such as chlorides, sulfates, and fluorides must not be allowed to build
46、 up in the solution as these tend to coat or etch the metal rather than clean the surface. Silver nitrate (AgNO3) may be used to precipitate out any chloride buildup, thus extending the life of the bath, but it is better to discard the contaminated solution and replace with a new solution. The solut
47、ion composition is indicated in Table II.3.4.2 Chromic-nitrate pickle: The chromic-nitrate pickle is not generally used where surface oxidation or corrosion products are to be removed but can be substituted for the chromic acid pickle specified in 3.4.1. It is used, as specified in 3.2.3.1, primaril
48、y for removing burned-on graphite lubricants. It is not satisfactory for the removal of sand or the effects of blasting and shall not be used for parts containing copper base inserts unless masked off. Lack of chemical action and a pH of 1.7 or higher indicates depletion of the bath. The bath may be
49、 controlled by additions of chromic acid to bring the solution back to the original pH range of 0.5-0.7. Large tanks may be revivified economically in this manner about 4 times after which tanks should be drained and refilled with new solution. Excessive revivification results in too great a consumption of chromic acid, excessive etching and staining of the magnesium. Actual time and temperature used should be regulated to produce satisfactory results. The solution composition is indicated in Table II.AMS-M-3171 SAE AMS-M-3171- 7 -TABLE IIAcid Pickling SolutionsComposition
