For alloys 7075 and 7178 a drop of 10% cadmium chloride solution will produce a dark discoloration within two minutes if
the scratch penetrates the clad. The cadmium chloride applied as above will not cause 2024 to discolor within two
3-249. When making the "spot" test to determine whether a scratch extends to the core, it is advisable for comparison
purposes to spot test an adjacent area in which there are no scratches. It is then easier to determine whether the residue
which remains is black or white.
3-250. Before making the "spot" test, the sheet area will be cleaned and degreased with solvent Federal Specification P-
D-680, Type I, or other suitable solvent, so that the caustic solution will react properly.
3-251. Caution will be exercised to make sure that all of the caustic solution is removed from the sheet by thorough
rinsing, since the caustic solution is very corrosive to aluminum and aluminum alloys. Care will be taken not to use
excessive amounts of the caustic solution for the same reason and it is preferable that only one drop be used for each
test. The caustic solution will be prepared fresh for each series of tests to be made.
3-252. DISPOSITION OF SCRATCHED SHEETS/ PARTS.
All scratched clad aluminum-alloy sheets will be utilized to the fullest extent. Serviceable portions of dam2ges
sheets will be used in the manufacture of smaller parts and assemblies. Only that portion of sheet that is scratched and
otherwise damaged beyond serviceability will be administratively condemned.
Parts (air weapon) shall be closely inspected as cited and if they do not meet specified requirement shall be
condemned and replaced as directed.
3-253. CLEANING OF ALUMINUM ALLOY SHEET (STOCK).
3-254. Solvent Cleaning. Stubborn or exceptionally oily sheets may be cleaned by using solvent, Federal Specification
P-D-680, Type I, before cleaning with alkali solution. The cleaning will be accomplished by brushing, soaking, scrubbing
and wiping. Material or equipment that would scratch or abrade the surface shall not be used. Also material shall not be
stored after solvent cleaning and prior to alk2line cleaning, unless solvent is completely removed from the surfaces of the
3-255. Alkali Cleaning Solution. Composition of solution is 4 to 6 oz of cleaner Specification MIL-C5543 to one gallon of
water. The material is cleaned by immersing in the solution (as prepared by instructions cited in paragraph 3-289) for 4-6
minutes, thoroughly rinsing in water (fresh tap) and then completely drying. Never pile/store material while damp, wet or
moist. Refer to T.O. 00-85A23-1 for packaging and storage.
Do not use strong alkali solution because it will etch the aluminum.
3-256. Preparation. Use water heated to a temperature of 170°F (77C). Add not more than one pound of cleaner at a
time. Prepare the solution in the following manner:
Fill the tank ½ to 2/3 full of water.
Carefully dissolve the alkaline cleaner.
Add water to operating level and stir thoroughly with a wooden paddle or other means.
3-257. Maintain solution in the following manner:
Add tap water to balance-up solution loss.
Make addition as required to maintain the active alkali concentration between 4 and 6 oz alkaline cleaner for
each gallon of water added and stir thoroughly.
Prepare a new solution when contamination impares the cleaning ability of the solution.
Clean the tank thoroughly before preparing a new solution.
3-258. Corrosion removal from Aluminum Alloy Sheets. Corrosion is removed by immersing the sheet in the following
acid cleaning solution:
When using acid solution wear approved clothing, acid resisting gloves, aprons/ coveralls,
face shields or respirator. If solution is splashed into eyes, flush thoroughly with water
immediately, and then report to dispensary. For special instructions, contact local safety
Nitric-Hydrofluoric Acid Cleaning. The solution shall consist of 1 gallon technical nitric acid (58-62% HNO3) (39.