ASTM D1732-03

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation:D1732–03
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 (e) 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:
PRELIMINARYTREATMENT 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 clean-
version coatings on, and remove contamination from, magne-
ing, alkaline solution treatments, and acid pickles not resulting
sium alloy surfaces. In general, however, apply conversion
in protective conversion coatings are suitable preliminary
coatings only to surfaces previously freed from all contamina-
treatments only for metal to be exposed under mildly corrosive
tion, including oxide, rolling-scale, corrosion product,
(indoor) exposures. When a high degree of corrosion protec-
burned-on drawing and forming lubricant, and the contamina-
tion and paint adhesion are desired, as in many outdoor
tion introduced by blast cleaning and fabrication operations.
environments, surface preparation by one of the above
Contamination in or under surface conversion coatings seri-
conversion-coatclassesisnecessary.Thehexavalentchromium
ously reduces their protective values (Note 2). For the removal
based methods given are not recommended as hexavalent
of tenacious surface contamination, such as rolling-scale or
chromium is a known carcinogen.
casting skin, an acid pickle to dissolve some of the actual
NOTE 1—Testing of Coatings—Quality control tests of coatings are surface is essential. When organic contamination, such as
frequently desirable, and these generally consist of exposures, with or
grease or oil, is also present, an initial degreasing operation in
without paint, to salt spray, humidity, or natural environments, with
solvent or in an alkaline degreasing solution is usually neces-
suitable procedures for assessing the degree of breakdown suffered after
sary to allow the subsequent acid to wet the surface. These
fixed time intervals. It is recommended that quality control tests of
matters are discussed in more detail under the headings of the
coatings shall be made as far as possible with high-purity material (for
2 specific cleaners or treatments (Note 3), as follows:
exampleAZ31Aalloy), the inherent corrosion rate of which is relatively
2.2 Alkaline Cleaners—Oil, grease, and old (but not baked)
consistent from batch to batch) and that precautions shall be taken to
remove surface contamination before coatings are applied. Such contami- chrome-pickle coatings are readily removed by most commer-
nationshallberemovedbyacidpicklingtoadepthofatleast0.001in.(25
cially available heavy-duty alkaline cleaners; but such cleaners
µm) per side.
are not suitable for removing oxide and the like, for which
purpose use acid pickles, preceded by alkaline cleaners.
1.2 This standard may involve hazardous materials, opera-
tions, and equipment. This standard does not purport to Remove graphite lubricant and also baked chrome-pickle
coatings by a solution conforming to the following composi-
address all of the safety concerns, if any, associated with its
use. It is the responsibility of the user of this standard to tion:
Caustic soda (NaOH) 12 oz (90 g)
Wetting agent 0.1 oz (0.74 g)
1
ThesepracticesareunderthejurisdictionofASTMCommitteeB08onMetallic Water (Note 4) 1 gal (1 litre)
and Inorganic Coatings and is the direct responsibility of Subcommittee B08.07 on
Soak the parts in the above cleaner for 10 to 20 min at
Chromate Conversion Coatings.
Current edition approved Sept. 10, 2003. Published Sept. 2003. Originally boiling-point,andatreatmentshallfolloweitherinthechromic
approved in 1960. Last previous edition approved in 1998 as D 1732-67 (1998).
acid-nitrate pickle described under 2.3.3 or, for parts machined
2
For information concerning magnesium and aluminum alloys, see ASTM
to fine tolerances, in the chromium trioxide solution described
Specification B 80, B 90, B 91, B 93, B 107, and B 209 covering these alloys, in the
under 2.3.1. After alkaline cleaning, rinse in water very
section on Aluminum and
...