ASTM D1732-03(2008)
(Practice)Standard Practices for Preparation of Magnesium Alloy Surfaces for Painting
Standard Practices for Preparation of Magnesium Alloy Surfaces for Painting
ABSTRACT
This specification covers chemical treatments and anodic treatments for preparation of magnesium alloy surfaces for printing. The procedure for preliminary treatment of surfaces using alkaline cleaners and acid cleaners are presented. Class I, type I (chrome pickle) surface preparation procedure is applicable to all forms of magnesium except certain special alloys containing silver. Class I, type II (sealed chrome pickle) surface preparation procedure is applicable to all types and forms of magnesium-based alloys, subject only to the limitations of class I, type I treatment. Class I, type III treatment is applicable to all types and forms of magnesium-based alloys except M1 alloy and certain rare-earth alloys similar to EK30A. Class II, type I (galvanic dichromate treatment) produce black coatings of good protective and pain-base qualities, and is applicable to all alloys and forms of magnesium, including M1 alloy. Class II, type II treatment is applicable to all forms and alloys of magnesium. Class II, type III treatment is applicable to all forms and alloys of magnesium, free from attachments or inserts of other metals.
SCOPE
1.1 These practices cover two classes of treatment for preparation of magnesium alloy surfaces for painting, as follows:
Class I—Chemical Treatments.
Class II—Anodic Treatments.
In general, the latter treatments are the more protective of the two classes. Mechanical (abrasive) treatments, solvent cleaning, alkaline solution treatments, and acid pickles not resulting in protective conversion coatings are suitable preliminary treatments only for metal to be exposed under mildly corrosive (indoor) exposures. When a high degree of corrosion protection and paint adhesion are desired, as in many outdoor environments, surface preparation by one of the above conversion-coat classes is necessary. The hexavalent chromium based methods given are not recommended as hexavalent chromium is a known carcinogen.
Note 1—Testing of Coatings—Quality control tests of coatings are frequently desirable, and these generally consist of exposures, with or without paint, to salt spray, humidity, or natural environments, with suitable procedures for assessing the degree of breakdown suffered after fixed time intervals. It is recommended that quality control tests of coatings shall be made as far as possible with high-purity material (for example AZ31A alloy), the inherent corrosion rate of which is relatively consistent from batch to batch) and that precautions shall be taken to remove surface contamination before coatings are applied. Such contamination shall be removed by acid pickling to a depth of at least 0.001 in. (25 μm) per side.
1.2 This standard may involve hazardous materials, operations, and equipment. This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. (See Note 11.)
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Designation: D1732 − 03(Reapproved 2008)
Standard Practices for
1
Preparation of Magnesium Alloy Surfaces for Painting
This standard is issued under the fixed designation D1732; the number immediately following the designation indicates the year of
original adoption 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.
This standard has been approved for use by agencies of the Department of Defense.
1. Scope establish appropriate safety and health practices and deter-
mine the applicability of regulatory limitations prior to use.
1.1 These practices cover two classes of treatment for
(See Note 11.)
preparation of magnesium alloy surfaces for painting, as
follows:
PRELIMINARY TREATMENT OF SURFACES
Class I—Chemical Treatments.
Class II—Anodic Treatments.
2. Procedure
Ingeneral,thelattertreatmentsarethemoreprotectiveofthe
2.1 Certain anodic treatments simultaneously produce con-
two classes. Mechanical (abrasive) treatments, solvent
version coatings on, and remove contamination from, magne-
cleaning, alkaline solution treatments, and acid pickles not
sium alloy surfaces. In general, however, apply conversion
resulting in protective conversion coatings are suitable prelimi-
coatings only to surfaces previously freed from all
nary treatments only for metal to be exposed under mildly
contamination, including oxide, rolling-scale, corrosion
corrosive (indoor) exposures. When a high degree of corrosion
product, burned-on drawing and forming lubricant, and the
protection and paint adhesion are desired, as in many outdoor
contamination introduced by blast cleaning and fabrication
environments, surface preparation by one of the above
operations. Contamination in or under surface conversion
conversion-coatclassesisnecessary.Thehexavalentchromium
coatings seriously reduces their protective values (Note 2). For
based methods given are not recommended as hexavalent
the removal of tenacious surface contamination, such as
chromium is a known carcinogen.
rolling-scale or casting skin, an acid pickle to dissolve some of
NOTE 1—Testing of Coatings—Quality control tests of coatings are
the actual surface is essential. When organic contamination,
frequently desirable, and these generally consist of exposures, with or
such as grease or oil, is also present, an initial degreasing
without paint, to salt spray, humidity, or natural environments, with
operation in solvent or in an alkaline degreasing solution is
suitable procedures for assessing the degree of breakdown suffered after
usually necessary to allow the subsequent acid to wet the
fixed time intervals. It is recommended that quality control tests of
coatings shall be made as far as possible with high-purity material (for surface. These matters are discussed in more detail under the
2
exampleAZ31Aalloy), the inherent corrosion rate of which is relatively
headings of the specific cleaners or treatments (Note 3), as
consistent from batch to batch) and that precautions shall be taken to
follows:
remove surface contamination before coatings are applied. Such contami-
nationshallberemovedbyacidpicklingtoadepthofatleast0.001in.(25
2.2 Alkaline Cleaners—Oil, grease, and old (but not baked)
µm) per side.
chrome-pickle coatings are readily removed by most commer-
1.2 This standard may involve hazardous materials,
cially available heavy-duty alkaline cleaners; but such cleaners
operations, and equipment. This standard does not purport to
are not suitable for removing oxide and the like, for which
address all of the safety concerns, if any, associated with its
purpose use acid pickles, preceded by alkaline cleaners.
use. It is the responsibility of the user of this standard to
Remove graphite lubricant and also baked chrome-pickle
coatings by a solution conforming to the following composi-
tion:
1
ThesepracticesareunderthejurisdictionofASTMCommitteeB08onMetallic
Caustic soda (NaOH) 12 oz (90 g)
and Inorganic Coatingsand is the direct responsibility of Subcommittee B08.07 on Wetting agent 0.1 oz (0.74 g)
Conversion Coatings. Water (Note 4) 1 gal (1 litre)
Current edition approved April 1, 2008. Published July 2008. Originally
Soak the parts in the above cleaner for 10 to 20 min at
approved in 1960. Last previous edition approved in 2003 as D1732-03. DOI:
boiling-point,andatreatmentshallfolloweitherinthechromic
10.1520/D1732-03R08.
2
For information concerning magnesium and aluminum alloys, see ASTM
acid-nitrate pickle described under 2.3.3 or, for parts machined
Specification B80, B90, B91, B93, B107, and B209 covering these alloys, in the
to fine tolerances, in the chromium trioxide solution described
section on Aluminum and Magnesium and Their Alloys, Annual Book of ASTM
u
...
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. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation:D1732–67(Reapproved 1998) Designation:D1732–03 (Reapproved 2008)
Standard Practices for
1
Preparation of Magnesium Alloy Surfaces for Painting
This standard is issued under the fixed designation D 1732; the number immediately following the designation indicates the year of
original adoption 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.
This standard has been approved for use by agencies of the Department of Defense.
1. Scope
1.1 These practices cover two classes of treatment for preparation of magnesium alloy surfaces for painting, as follows:
Class I—Chemical Treatments. Chemical Treatments.
Class II—Anodic Treatments.
In general, the latter treatments are the more protective of the two classes. Mechanical (abrasive) treatments, solvent cleaning,
alkaline solution treatments, and acid pickles not resulting in protective conversion coatings are suitable preliminary treatments
only for metal to be exposed under mildly corrosive (indoor) exposures. When a high degree of corrosion protection and paint
adhesion are desired, as in many outdoor environments, surface preparation by one of the above conversion-coat classes is
necessary. The hexavalent chromium based methods given are not recommended as hexavalent chromium is a known carcinogen.
NOTE 1—Testing of Coatings—Qualitycontroltestsofcoatingsarefrequentlydesirable,andthesegenerallyconsistofexposures,withorwithoutpaint,
to salt spray, humidity, or natural environments, with suitable procedures for assessing the degree of breakdown suffered after fixed time intervals.Itis
2
recommended that quality control tests of coatings shall be made as far as possible with high-purity material (for example AZ31A alloy), the inherent
corrosion rate of which is relatively consistent from batch to batch) and that precautions shall be taken to remove surface contamination before coatings
are applied. Such contamination shall be removed by acid pickling to a depth of at least 0.001 in. (25 µm) per side.
1.2 This standard may involve hazardous materials, operations, and equipment. This standard does not purport to address all
of the safety problems concerns, if any, associated with its use. It is the responsibility of whoever uses the user of this standard
to consult and establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to
use. (See Note 11.)
PRELIMINARYTREATMENT OF SURFACES
2. Procedure
2.1 Certain anodic treatments simultaneously produce conversion coatings on, and remove contamination from, magnesium
alloy surfaces. In general, however, apply conversion coatings only to surfaces previously freed from all contamination, including
oxide, rolling-scale, corrosion product, burned-on drawing and forming lubricant, and the contamination introduced by blast
cleaning and fabrication operations. Contamination in or under surface conversion coatings seriously reduces their protective
values(Note2).Fortheremovaloftenacioussurfacecontamination,suchasrolling-scaleorcastingskin,anacidpickletodissolve
some of the actual surface is essential. When organic contamination, such as grease or oil, is also present, an initial degreasing
operationinsolventorinanalkalinedegreasingsolutionisusuallynecessarytoallowthesubsequentacidtowetthesurface.These
matters are discussed in more detail under the headings of the specific cleaners or treatments (Note 3), as follows:
2.2 Alkaline Cleaners—Oil, grease, and old (but not baked) chrome-pickle coatings are readily removed by most commercially
available heavy-duty alkaline cleaners; but such cleaners are not suitable for removing oxide and the like, for which purpose use
acid pickles, preceded by alkaline cleaners. Remove graphite lubricant and also baked chrome-pickle coatings by a solution
conforming to the following composition:
Caustic soda (NaOH) 12 oz (90 g)
Wetting agent 0.1 oz (0.74 g)
Water (Note 4) 1 gal (1 litre)
Soak the parts in the above cleaner for 10 to 20 min at boiling-point, and a treatment shall follow either in the chromic
1
These practices are under the jurisdiction ofASTM Committee B-8B08 on Metallic and Inorganic Coatings and is the direct responsibility of Subcommittee B08.07 on
Chemical Conversion Coatings.
Current edition approved Sept. 8, 1967.April 1, 2008. Published November 1967.July 2008. Originally published as D1732-60.approved in 1960. Last previous e
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