77 Questions
What is the primary reason corrosion is most efficient in waters containing salts?
The high conductivity of the solution
What type of corrosion is caused by direct contact between a metal and an alkaline or acidic liquid?
Direct chemical attack
Which of the following can affect the theoretical rate of a chemical attack on a metal?
The formation of a protective film on the metal surface
Which type of acid is especially active in corroding aluminum?
Sulfuric acid
Which of the following is more likely to cause corrosion on aluminum structures?
Strong alkaline solutions
What is the purpose of using a weak solution of chromic or phosphoric acid as a surface treatment on metal?
To form a protective film on the metal surface
What is the mechanism by which water can cause corrosion on aluminum structures on a concrete floor?
The water leaches lime from the cement to form an alkaline solution
Which type of hydraulic fluid can cause corrosion on metals?
Phosphate ester hydraulic fluid (Skydrol)
What is the main reason that tarnish removal is critical on gold components?
The very thin coatings used on gold components are susceptible to tarnish
What is the main advantage of using tin plating on avionic components?
Tin offers the best combination of solderability and corrosion resistance
What is the main issue with using tin plating on components?
Tin plating tends to grow 'whiskers' on tin-plated wire and other plated applications
What is the main reason that gold plating over silver or copper in thin layers accelerates corrosion?
Gold plating over less noble metals like silver or copper leads to corrosion at pores or pinholes in the gold
What is the name of the brittle compound that can form when gold is bonded to aluminium?
Purple plague
What is the effect of the growth of the 'purple plague' compound on microelectronic interconnection bonds?
It can cause failure in microelectronic interconnection bonds
What is the main reason that a slight deposit will appear as a darkening of reflecting surfaces on gold?
Gold does not normally corrode, but a slight deposit will appear as a darkening
What is the main reason that tin plating is used on avionic RF shields, filters, crystal covers, and automatic switching devices?
Tin offers the best combination of solderability and corrosion resistance
What is the primary cause of most corrosion encountered by aircraft maintenance engineers?
Electrochemical (galvanic) action
What is the main effect of corrosion on aircraft structures?
Severe loss of strength
Which of the following is NOT a required component for electrochemical corrosion to occur?
Electrical insulation between the metals
What is the primary way for aircraft maintenance engineers to prevent corrosion?
Preventing or removing one or more of the requirements for corrosion
Which of the following is NOT a requirement for electrochemical corrosion to occur?
A uniform metal surface
What is the main purpose of the cathode in the electrochemical corrosion process?
To conduct the flow of electrons
What is the main role of the electrolyte in the electrochemical corrosion process?
To carry current by providing a path for the movement of ions
Why is it almost impossible to completely prevent corrosion?
Corrosion is a natural process
What is the primary use of nickel as a plating metal in aviation?
All of the above
What can happen if scum forms along the edge of a seal in an integral fuel tank?
The sealant may pull away from the structure, causing a leak and an expensive resealing operation
What is the most widely used material for aircraft construction?
Aluminium and its alloys
What is a potential issue with using pure nickel as an electroless coating?
It is subject to pitting corrosion
Which of the following is a characteristic of aluminium alloys?
They are subject to pitting, intergranular corrosion and stress corrosion cracking
What is the primary use of copper and copper-based alloys in avionics systems?
All of the above
Why is aluminium considered anodic?
Because it is anodic to most other metals
What is a common sign of copper corrosion in aviation?
Accumulation of blue or blue-green corrosion products
What is the effect of changes in the surface condition of copper and copper-based alloys in aviation?
They are generally not dangerous and have no effect on the part
What can happen when aluminium comes into contact with other metals?
Galvanic corrosion of the aluminium will occur
What is the purpose of adding nickel to stainless steel alloys?
To increase the alloy's resistance to stress corrosion
What can help increase the corrosion resistance of aluminium under mild corrosive conditions?
The formation of a tightly adhering oxide film
What is the main drawback of using aluminium in aircraft construction?
It is susceptible to corrosion
What is a potential issue with using nickel-based alloys in high-temperature areas like engines?
They are subject to hot corrosion attack and embrittlement when sulfur-containing gases are present
What is the main reason why no metal is totally resistant to corrosion?
Metals are inherently susceptible to corrosion
What might be a visible sign indicating the presence of pitting corrosion on a metal surface?
Presence of white powder clumps
What is the result if pitting corrosion continues untreated?
Metal thickness is converted into salts
How are aluminium alloys primarily held together according to micro-photographs?
Interconnected by tiny grains
What effect does heat treatment have on aluminium alloy during the process?
It dissolves alloying agents into each other
What is a characteristic sign that intergranular corrosion may be occurring?
Appearance of dark, narrow lines
What can happen if uniform surface corrosion progresses to pitting, and pitting remains untreated?
Pits may eat completely through the metal
How are the grains in aluminium alloys held together in micro-photographs?
By chemical bonds between atoms
What type of appearance may suggest the presence of intergranular corrosion?
Development of dark, narrow lines
What is the primary cause of galvanic corrosion in aircraft structures?
Riveting dissimilar metal skins together
What is the main effect of stress corrosion on aircraft structures?
Rapid crack growth
What is the primary effect of surface corrosion on aircraft structures?
Conversion of metal to corrosion salts
What is the main purpose of removing tarnish from gold components in aircraft?
To maintain the reflective properties of the surface
What is the primary reason that corrosion is most efficient in waters containing salts?
The salts act as an electrolyte
What is the main reason that aluminium is considered anodic?
Aluminium is more reactive than other metals
What is the main drawback of using aluminium in aircraft construction?
Aluminium is prone to galvanic corrosion
What is the primary use of copper and copper-based alloys in avionics systems?
Copper is used for its high electrical conductivity
What is the main cause of fretting corrosion?
Destruction of the protective film due to rubbing action
What is a characteristic of exfoliation corrosion?
Results in material delamination along grain boundaries
In what scenario does fretting corrosion typically occur?
When there is significant movement between surfaces
What distinguishes exfoliation corrosion from other types of corrosion?
It predominantly affects materials with layered grain structures
How can fretting corrosion be visually identified around rivets?
By the presence of dark deposits around the rivet heads
What is the consequence of debris not being able to escape between surfaces affected by fretting corrosion?
The debris further erodes the surfaces as an abrasive
Why is it important to replace rivets showing signs of fretting corrosion promptly?
To avoid further damage and potential failure
What distinguishes exfoliation corrosion from other forms of corrosion in terms of affected materials?
Materials that are extruded.
What happens to the strength of a metal affected by intergranular corrosion?
It decreases significantly
How do microbes contribute to corrosion in aircraft fuel tanks?
They promote the growth of scum that leads to corrosion
What is the recommended remedy for exfoliation corrosion on aircraft structures?
Complete removal of affected sections
In what type of conditions can water entrained in aircraft fuel condense out?
High-altitude, low-temperature flight conditions
What role does the dark insides of fuel tanks play in microbiological corrosion?
Promotes microbial growth
How do microbes in aircraft fuel tanks feed and grow?
By feeding on hydrocarbon fuel and multiplying
What is the primary reason for the corrosion rate of magnesium alloys increasing when immersed in water or subjected to moisture?
The natural oxide-carbonate film formed on magnesium alloys provides insufficient corrosion protection.
What is the primary concern regarding the use of titanium at high temperatures?
Titanium readily absorbs gases from the surrounding air, leading to brittleness.
What is the primary reason for the need to electrically insulate titanium from other metals?
To prevent galvanic corrosion of the other metal coupled with titanium.
Which statement is true regarding the oxide film formed on titanium and its alloys?
The oxide film forms almost immediately upon contact with air and is extremely adherent.
What is a potential issue when titanium comes into contact with a corroding metal?
Titanium may absorb hydrogen from the corroding metal and become brittle.
Which statement is true regarding the corrosion resistance of titanium and its alloys?
Titanium and its alloys are highly corrosion resistant due to the protective oxide film.
What is a potential issue with certain titanium alloys when exposed to chlorides or chlorinated solvents?
Stress corrosion cracking may be induced under certain conditions.
What is the primary reason for the high corrosion resistance of titanium and its alloys?
The formation of a tightly adherent oxide film on the surface.
Explore the electrochemical processes responsible for corrosion in aircraft, leading to the transformation of metals into salts and oxides. Learn about the impact on structural integrity and the simple mechanics behind this complex phenomenon. Original text from Aviation Australia.
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