1、Designation: D 1731 03Standard Practices forPreparation of Hot-Dip Aluminum Surfaces for Painting1This standard is issued under the fixed designation D 1731; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision
2、. 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 These practices describe procedures for the preparationof hot-dip aluminum surfaces for painting.1.2 This standard may involve haz
3、ardous materials, opera-tions, and equipment. This standard does not purport toaddress all of the safety concerns, if any, associated with itsuse. It is the responsibility of the user of this standard toestablish appropriate safety and health practices and deter-mine the applicability of regulatory
4、limitations prior to use.2. Referenced Documents2.1 ASTM Standards:D 609 Practice for Preparation of Cold-Rolled Steel Panelsfor Testing Paint, Varnish, Conversion Coatings and Re-lated Coating Products22.2 Military Standards:MIL-C-5541 Chemical Conversion Coatings on Aluminumand Aluminum Alloys33.
5、Types of Surface Preparations3.1 Two types of surface preparations are covered as fol-lows:3.1.1 Solvent Cleaning, and3.1.2 Chemical Treatments.3.2 These two types cover several methods as described inSection 5. Variations in surface treatment produce end condi-tions which differ and which do not ne
6、cessarily yield identicalresults when paints are applied. Service conditions will dictatethe type of surface preparation that should be selected.4. Solvent Cleaning4.1 The surfaces may be prepared for painting by any of themethods for solvent cleaning described in 4.2 and 4.3.4.2 Method 1Manual swab
7、bing or dip washing with asolvent such as mineral spirits or high flask solvent naphtha. Itis extremely difficult to produce a clean metal surface by thismethod. Accumulated contaminants in the solvent or on theswab are frequently redeposited on the surface being prepared.4.3 Method 2Solvent spray c
8、leaning in accordance withMethod A, Procedure 1 of Practice D 609.4.4 Method 3Vapor degreasing in special equipment inaccordance with the latest revision of Method A, Procedure 2of Practice D 609, employing trichlorethylene or perchloreth-ylene vapor. Solvent cleaning does not disturb the natural ox
9、idefilm on the metal and may prove adequate for some applica-tions.5. Chemical Treatment5.1 The surfaces may be prepared for painting by any of themethods for chemical treatment (Note 1) described in 5.2 to5.9:NOTE 1Materials and procedures employed in these methods oftreatment are available from a
10、number of sources as proprietary com-pounds or methods. Selection may be made from available sources. Thehexavalent chromium methods given are not recommended as hexavalentchromium is a known carcinogen.5.2 Method 1, Alkaline CleanersEtching alkaline solu-tions, such as caustic soda, should be avoid
11、ed because of thepossibility of dissolving away the aluminum coating therebyexposing the base metal. Since inhibited alkaline cleaners donot etch the surface, they can be used to remove grease, oil, andother organic solids from hot dip aluminum. After alkalicleaning, the surface should be thoroughly
12、 rinsed with cleanwater. Most often alkaline-cleaned surfaces are subsequentlyprocessed by one of the following methods, described in5.3-5.9.5.3 Method 2, Alcoholic Phosphoric Acid CleanersThistreatment involves the use of an aqueous solution of phospho-ric acid with alcohol or other organic solvent
13、s, together withwetting agents, emulsifying agents, etc. The solution may beapplied by swabbing or dipping (preferably at a temperature of70 to 90F (21 to 32C). The solution should remain on thesurface for several minutes, followed by thorough rinsing withclean water. A very thin phosphate film is f
14、ormed which tendsto protect the metal and promote paint adhesion.NOTE 2Materials meeting the requirements of the latest revision ofU.S. Military Specification MIL-M-10578B may be used.1These practices are under the jurisdiction of ASTM Committee B08 on Metallicand Inorganic Coatings and is the direc
15、t responsibility of Subcommittee B08.07 onChromate Conversion Coatings.Current edition approved Sept. 10, 2003. Published Sept. 2003. Originallyapproved in 1960. Last previous edition approved in 1998 as D 1731 67 (1998).2Annual Book of ASTM Standards, Vol 06.01.3Available from Standardization Docum
16、ents Order Desk, DODSSP, Bldg. 4,Section D, 700 Robbins Ave., Philadelphia, PA 19111-50981Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.5.4 Method 3, Acid Fluoride DeoxidizerThis treatmentincludes the use of nitric or sulfuric acid
17、with chromiumtrioxide and a fluoride. It provides a clean and uniform surfacewithout undue roughening and is effective for removinginorganic soils and any film formed during the production ofthe hot dip aluminum. The deoxidizing solution is generallyused at a temperature of 70 to 130F (21 to 54C) (d
18、ependingon the alloy and the amount of film) and is followed by a waterrinse.NOTE 3Before applying the treatments according to Chemical Treat-ment Methods 3, 4, 5, 6 and 7, the aluminum surfaces should be freed ofgrease, oil or other foreign material by means of the procedure describedin Solvent Cle
19、aning Method 3, Chemical Treatment Method 1 or any othersuitable method.5.5 Method 4, Crystalline Phosphate TreatmentThissurface-coating method consists in reacting the aluminumsurface in a 130 to 145F (54 to 63C) (approximately) zincacid-phosphate solution containing oxidizing agents and othersalts
20、 for accelerating the coating action. The aluminum surfaceis converted to a crystalline, phosphate coating of the propertexture adapted to inhibit corrosion and increase the adherenceand durability of any applied paint film. The phosphate coatingprocess may be carried out by immersion or spray appli
21、cation.The aluminum surface is converted to the phosphate coating byimmersion in the processing solution for 30 s to 4 min, or byspraying the solution for 10 s to 2 min (Note 3).5.6 Method 5, Amorphous Phosphate Treatment (see Note4)This process comprises treatment of clean aluminumsurfaces in a 90
22、to 125F (32 to 51C) aqueous solutioncomprising phosphoric, hydrofluoric acids and chromium tri-oxide. The aluminum surface is converted to a thin, adherent,amorphous coating, iridescent green to gray green in color,depending upon the aluminum alloy treated, which inhibitscorrosion and increases the
23、adherence and durability of appliedpaint films. The coating process may be carried out byimmersion or spray application. The time of treatment willvary from 15 to 45 s for the spray process and 30 s to 3 min forthe immersion application (Note 3).5.7 Method 6, Carbonate Chromate Treatment (see Note4)
24、This process comprises treatment in a 160 to 180F (71 to82C) dilute solution of sodium carbonate and potassiumchromate for periods from 2 to 20 min, followed by a waterrinse. The surface is then given a final treatment in a 150 to160F (66 to 71C), 5% potassium dichromate solution fol-lowed by a fina
25、l rinse. The treatment produces a thin, adherent,conversion coating on the surface, increasing the corrosionresistance of the metal and promoting paint adhesion (Note 3).5.8 Method 7, Amorphous Chromate Treatment (see Note4)This process comprises treatment of clean aluminumsurfaces in aqueous chromi
26、um trioxide solutions containingsuitable accelerating agents such as fluoride-containing mate-rials. The aluminum surface is converted to an adherent,amorphous, mixed metallic oxide coating, iridescent golden tolight brown in color, which increases the corrosion resistanceand the adherence and durab
27、ility of any applied paint film. Thecoating process may be carried out by immersion, spray orbrush application, at 70 to 130F (21 to 54C), in from 15 s to5 min contact time. It may be necessary to precede thistreatment with a deoxidizer as described in Method 3 (see Note3).NOTE 4Most of the treatmen
28、ts conforming to Chemical TreatmentMethods 5, 6, and 7, comply with the requirements of the latest revisionof U.S. Military Specification MIL-C-5541.5.9 Method 8, Acid-Bound Resinous Treatment (see Note5)This surface treatment is based on the deposition of anacid-bound resinous film of approximately
29、 0.3 to 0.5 mils (7.6to 12.7 m) in thickness on the aluminum surface in such amanner as to enhance the adhesion of subsequently appliedpaint coatings. The treatment is based on three primarycomponents: a hydroxyl-containing resin; a pigment capable ofreacting with the resin and an acid; and an acid
30、capable ofinsolubilizing the resin by reacting with the resin, the pigmentand the metal substrate. The aluminum surface should bepretreated by Solvent Cleaning Methods 1, 2 or 3 or ChemicalTreatment Methods 1 or 2 prior to the application of thistreatment. The film may be applied by brush, spray, or
31、 dip.Under normal conditions it shall dry sufficiently for recoatingwithin 30 min. The film has good adhesion to the metalsubstrate and promotes good adhesion of most subsequentorganic coatings to itself.NOTE 5Materials meeting the requirements of the latest revision ofU.S. Military Specification MI
32、L-C-15328 may be used to apply toChemical Treatment Method 8.6. Keywords6.1 hot-dip aluminum; pretreatment for painting; surfacetreatmentsASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this st
33、andard are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years a
34、ndif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee,
35、 which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org).D1731032
