ASTM D1732-67(1998)
(Practice)Standard Practices for Preparation of Magnesium Alloy Surfaces for Painting
Standard Practices for Preparation of Magnesium Alloy Surfaces for Painting
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. 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 [mu]m) 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 associated with its use. It is the responsibility of whoever uses this standard to consult and establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.> (See Note 11.)
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Designation: D 1732 – 67 (Reapproved 1998)
Standard Practices for
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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 PRELIMINARY TREATMENT OF SURFACES
1.1 These practices cover two classes of treatment for
2. Procedure
preparation of magnesium alloy surfaces for painting, as
2.1 Certain anodic treatments simultaneously produce con-
follows:
version coatings on, and remove contamination from, magne-
Class I—Chemical Treatments. Class II—Anodic
sium alloy surfaces. In general, however, apply conversion
Treatments.
coatings only to surfaces previously freed from all contamina-
In general, the latter treatments are the more protective of the
tion, including oxide, rolling-scale, corrosion product,
two classes. Mechanical (abrasive) treatments, solvent clean-
burned-on drawing and forming lubricant, and the contamina-
ing, alkaline solution treatments, and acid pickles not resulting
tion introduced by blast cleaning and fabrication operations.
in protective conversion coatings are suitable preliminary
Contamination in or under surface conversion coatings seri-
treatments only for metal to be exposed under mildly corrosive
ously reduces their protective values (Note 2). For the removal
(indoor) exposures. When a high degree of corrosion protec-
of tenacious surface contamination, such as rolling-scale or
tion and paint adhesion are desired, as in many outdoor
casting skin, an acid pickle to dissolve some of the actual
environments, surface preparation by one of the above
surface is essential. When organic contamination, such as
conversion-coat classes is necessary.
grease or oil, is also present, an initial degreasing operation in
NOTE 1—Testing of Coatings—Quality control tests of coatings are
solvent or in an alkaline degreasing solution is usually neces-
frequently desirable, and these generally consist of exposures, with or
sary to allow the subsequent acid to wet the surface. These
without paint, to salt spray, humidity, or natural environments, with
matters are discussed in more detail under the headings of the
suitable procedures for assessing the degree of breakdown suffered after
specific cleaners or treatments (Note 3), as follows:
fixed time intervals. It is recommended that quality control tests of
2.2 Alkaline Cleaners—Oil, grease, and old (but not baked)
coatings shall be made as far as possible with high-purity material (for
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example AZ31A alloy), the inherent corrosion rate of which is relatively
chrome-pickle coatings are readily removed by most commer-
consistent from batch to batch) and that precautions shall be taken to
cially available heavy-duty alkaline cleaners; but such cleaners
remove surface contamination before coatings are applied. Such contami-
are not suitable for removing oxide and the like, for which
nation shall be removed by acid pickling to a depth of at least 0.001 in. (25
purpose use acid pickles, preceded by alkaline cleaners.
μm) per side.
Remove graphite lubricant and also baked chrome-pickle
1.2 This standard may involve hazardous materials, opera-
coatings by a solution conforming to the following composi-
tions, and equipment. This standard does not purport to
tion:
address all of the safety problems associated with its use. It is
Caustic soda (NaOH) 12 oz (90 g)
the responsibility of whoever uses this standard to consult and
Wetting agent 0.1 oz (0.74 g)
Water (Note 4) 1 gal (1 litre)
establish appropriate safety and health practices and deter-
mine the applicability of regulatory limitations prior to use.
Soak the parts in the above cleaner for 10 to 20 min at
(See Note 11.)
boiling-point, and a treatment shall follow either in the chromic
acid-nitrate pickle described under 2.3.3 or, for parts machined
to fine tolerances, in the chromium trioxide solution described
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These practices are under the jurisdiction of ASTM Committee B-8 on Metallic under 2.3.1. After alkaline cleaning, rinse in water very
and Inorganic Coatings and is the direct responsibility of Subcommittee B08.07 on
thoroughly. Alkaline cleaners may be held in plain steel tanks.
Chemical Conversion Coatings.
2.3 Acid Cleaners (Note 1)—Acid picking removes mill-
Current edition approved Sept. 8, 1967. Published November 1967. Originally
scale, oxide, corrosion product, and the like. Use as a prelimi-
published as D 1732-60. Last previous edition D 1732-66.
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For information concerning magnesi
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