MIL-DTL-5541F
supplier cannot be mixed or used to strengthen an existing solution from another material
supplier. As the chemical coating materials are proprietary products, the ingredients, processes,
the method of application (e.g., spray, brush, or immersion), and the equipment required for
application of the coating may vary. Contractors and military activities must take this into
account in acquisition, in the design of parts, and in the establishment of facilities. Detail
drawing of parts requiring treatment in accordance with this specification should specify class
1A or 3, where applicable the required type, I or II, and any paint finishing systems required to
meet the performance desired. If the coating class is not specified, class 1A is recommended.
6.6 Cleaners. Use of a non-etch cleaner is preferred, particularly on wrought alloys. If an
etch is used, caution must be taken to prevent pitting or intergranular attack. This is particularly
important when using an alkaline etch because the aluminum tends to be more soluble than its
alloying elements and existing intermetallics, such as copper, which may be further exposed. As
a result, alkaline etching should be avoided (particularly when cleaning assembled structures). If
an alkaline etch is used, it should always be followed by an acid neutralization step.
6.7 Abrasion resistance. The abrasion resistance of chemical coatings is relatively low.
Coatings are reasonably durable when subjected only to moderate handling, but are readily
removed by severe wear or erosion. However, cold forming operations, when performed with
care, can generally be performed on treated metals without appreciable damage to the coatings.
6.8 Visual appearance. The simplest way to evaluate a conversion coating is to observe
color, continuity in appearance, smoothness and adhesion to the base metal (see 3.5). Visual
examination is performed to ensure that proper cleaning and coating procedures were used such
that a coating with sufficient protection exists over the entire part. Materials qualified under
MIL-DTL-81706 produce coatings that range in color from clear/colorless to iridescent yellow,
brown, gray, or blue. It may be possible to develop acceptable color levels for a particular
coating system by use of color chips. The following circumstances may exist that relate to color
uniformity:
a. When several alloys are processed with the same conversion chemical, color may vary
from alloy to alloy.
b. Due to the high level of impurities and oxidation on the surfaces of aluminum welds and
castings, color may not be as uniform as that obtained by treating wrought alloys.
c. Dark spots may result from dripping or rundown of the conversion chemicals when the
parts are lifted out of the treatment tank. A small amount of spotting does not result in
coating degradation but must be minimized by quickly rinsing the parts after treatment, and
use of proper racking techniques.
Visual examination does not reveal if the protective value of the coating has been impaired by
contamination or by overheating during drying. If a clear coating is required, inspection
difficulties may arise because visual inspection does not reveal the presence of a coating. For
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