Practice Quiz #1 Flashcards
For which of the following reasons would a water break test be conducted?
Alodine can be applied to a surface after all traces of corrosion have been removed.
The surface should be chemically cleaned until it supports an unbroken water film. Any
breaks in the film of rinse water show that there some wax, grease, or oil on the surface,
and further cleaning must be done.
Corrosion should be removed from magnesium parts with a
stiff, nonmetallic brush
Mechanical removal of corrosion from magnesium parts should be limited to the use of
stiff hog-bristle brushes and similar nonmetallic cleaning tools.
Corrosion caused by galvanic action is the result of
Galvanic corrosion is caused by an electrolytic action that takes place when two metals
that have a different place in the galvanic scale are in contact with each other and are
covered with an electrolyte. The more anodic of the metals reacts with the electrolyte
and some of it changes into salts (it corrodes).
How may magnesium engine parts be cleaned?
Wash with a commercial solvent, decarbonize, and scrape or grit blast.
Magnesium engine parts are cleaned by washing them with a commercial solvent such
as naphtha or Stoddard solvent, then soaking them in a decarbonizer that has been
proven safe for magnesium. Any hard deposits that are not removed by this treatment
can be removed with a scraper or with a grit blast.
What may be used to remove corrosion from highly stressed steel surfaces?
Any corrosion on the surface of a highly stressed steel part is potentially dangerous,
and all of the corrosion products must be removed.
The removal can be done with mild
abrasive papers such as rouge or fine grit aluminum oxide, or fine buffing compounds
on cloth buffing wheels.
Intergranular corrosion in aluminum alloy parts
Intergranular corrosion forms along the grain boundaries within an aluminum alloy.
Since this type of corrosion does not necessarily extend all the way to the surface of the
metal in its early stages, it is quite possible for intergranular corrosion to reach an
advanced state before it shows up on the surface.
A primary cause of intergranular corrosion is
One of the primary causes for intergranular corrosion is improper heat treatment.
If there is a delay in the time between the removal of a metal part from the heat treatment
oven and the time the part is quenched, the grains of the metal have an opportunity to
grow large enough that an electrical potential exists across the grain boundaries. This
potential within the metal causes the formation of intergranular corrosion.
Why is it important not to rotate the crankshaft after the corrosion preventive
mixture has been put into the cylinders on engines prepared for storage?
When a reciprocating engine is prepared for storage, the inside of the cylinders are
sprayed with a mixture of engine oil and a preservative oil. The oil mixture forms a seal
on the cylinder wall and across the top of the piston.
This mixture keeps air and
moisture away from the metal surface. If the propeller is turned, the pistons will move
and break the seal so that air and moisture can reach the cylinder walls and cause them
to rust.
Which of these materials is the most anodic?
Some of the common metals in the order of their electrochemical activity are: (Most
anodic) Magnesium Zinc Cadmium 7075 Aluminum alloy 2024 Aluminum alloy Mild
steel Copper Stainless Steel Chromium Gold (Most cathodic)
What should be done to prevent rapid deterioration when oil or grease come in
contact with a tire?
When an aircraft tire comes in contact with oil or grease, remove all of the excess
material by wiping it with a dry cloth.
Then wash the tire with a solution of mild soap and
warm water. Rinse the tire with fresh water and dry it with compressed air.
Spilled mercury on aluminum
Mercury spilled in an aircraft requires immediate action for its isolation and recovery to
prevent it from causing corrosion damage and embrittlement of the aluminum structural
components. Mercury is highly toxic and spreads very easily from one surface to
another.
Why is it important not to rotate the crankshaft after the corrosion preventive
mixture has been put into the cylinders on engines prepared for storage?
When a reciprocating engine is prepared for storage, the inside of the cylinders are
sprayed with a mixture of engine oil and a preservative oil. The oil mixture forms a seal
on the cylinder wall and across the top of the piston. This mixture keeps air and
moisture away from the metal surface. If the propeller is turned, the pistons will move
and break the seal so that air and moisture can reach the cylinder walls and cause them
to rust.
A primary reason why ordinary or otherwise nonapproved cleaning compounds
should not be used when washing aircraft is because their use can result in
hydrogen embrittlement in metal structures.
Some nonapproved commercial cleaning compounds can cause a chemical reaction
with some of the metals used in aircraft structure. This reaction releases hydrogen gas
that can be absorbed into the metal and cause hydrogen embrittlement which weakens
the metal and can cause cracking and failure.
The lifting or flaking of the metal at the surface due to delamination of grain
boundaries caused by the pressure of corrosion residual product buildup is
called
exfoliation.
Exfoliation corrosion is a severe form of intergranular corrosion that normally forms in
extruded metal. When metal is extruded, its grain structure is basically arranged in a
series of layers. If an extrusion is improperly heat-treated, the grains are enlarged to the
extent that intergranular corrosion can form along the grain boundaries within the metal.
Severe intergranular corrosion in an extruded material causes it to delaminate (the
layers of the metal to push apart). The surface of the metal lifts or flakes off.
Corrosion should be removed from magnesium parts with a
Mechanical removal of corrosion from magnesium parts should be limited to the use of
stiff hog-bristle brushes and similar nonmetallic cleaning tools.
