CHAPTER 6 - MATERIALS AND CORROSION Flashcards by Abi Faulkner

GENERAL INTRODUCTION
What two categories are metals and alloys separated into?

Ferrous and Non-ferrous

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GENERAL INFOMATION
How would you define an alloy?

The addition of other metals, or substances, to a basic metal, in order to obtain desirable properties

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STANDARD AND SPECIFICATIONS
Why are standards beneficial to business and to individuals?

Defines accurate measurement, lowering production costs, improves product performance, quality, uniformity, interoperability and functionality
Many benefits

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STANDARDS AND SPECIFICATIONS
How do British, French and American Standards each measure a metal’s thickness?

British: Standard Wire Gauge
French: Millimetres
American: Thousands of an inch

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STANDARDS AND SPECIFICATIONS
State which standards are oldest to newest between British, French and American..

British 1901
American 1904
French 1943

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STANDARDS AND SPECIFICATIONS
Who produces the International Standards? And their correct abbreviation..

ISO
International Organisation for Standardisation

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STANDARDS AND SPECIFICATIONS
Which standard system is most frequently used in MOD?

Defence Standard

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STANDARD AND SPECIFICATIONS
Why do we need Proof of Conformity for metallic and non-metallic materials?
Where is this from?

To show it is safe to be used on an aircraft
Give directly from the contractor

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STANDARDS AND SPECIFICATIONS
What materials do not require Certificate of Conformity?

Materials supplied under Federal Military Stock (FMS)

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COLOUR CODING
What scheme is used for rapid identification but should not be used as sole means of identifications?

Colour coding

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COLOUR CODING
What material pieces are not colour coded?

Thin gauge sheets

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FERROUS METALS
What is the difference between ferrous and non-ferrous metals?

Ferrous metals contain mostly iron

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HEAT TREATMENT OF SHEET ALLOYS
Which treatment is used to change the metal into a very soft and malleable condition?

Annealing

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HEAT TREATMENT OF SHEET ALLOYS
Which treatment changes the metal into a soft condition? It also gives the metal some specified qualities when it has aged?

Heat treatment

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HEAT TREATMENT OF SHEET ALLOYS
Why is Refrigerated Storage used as a treatment?

Slows down the natural age process to keep the metal in its heat treated or quenched condition for longer

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HEAT TREATMENT OF SHEET ALLOYS
What is another term for precipitation (accelerated) treatment?

Artificial Age Treatment

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HEAT TREATMENT OF SHEET ALLOYS
What is the benefits of Artificial Age Treatment?

Maximum strength of an alloy which can be heat treated
It is necessary to artificially age the material

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HEAT TREATMENT OF SHEET ALLOYS
What process occurs are room temperature?

Natural Age Process

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HEAT TREATMENT OF SHEET ALLOYS
What happens to all alloys which go through the natural age process?

Their strength begins to increase immediately when they begin to cool

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AIRCRAFT ENVIRONMENTAL DAMAGE PREVENTION AND CONTROL
What does the term Environmental Damage mean?

Describes the physical degradation of material properties as a direct result of interaction with the climate or environment

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AIRCRAFT ENVIRONMENTAL DAMAGE PREVENTION AND CONTROL
What three major factors are included with ED?

Corrosion
Erosion
Degradation of surface finish and composite material properties

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AIRCRAFT ENVIRONMENTAL DAMAGE PREVENTION AND CONTROL
What is the most significant form of ED?

Corrosion

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AIRCRAFT ENVIRONMENTAL DAMAGE PREVENTION AND CONTROL
What are the 4 major effects of corrosion?

Reduce static strength
Initiate stress corrosion cracking
Shorten fatigue life
Detrimentally affects avionics and mechanical equipment

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AIRCRAFT ENVIRONMENTAL DAMAGE PREVENTION AND CONTROL
What should a permanent protective metallic coating have in comparison to the metal

A higher resistance to corrosion

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AIRCRAFT ENVIRONMENTAL DAMAGE PREVENTION AND CONTROL What are the three general classes of coatings? Explain how the work..

1. Metallic Coatings - protects by preventing access of the corrosive agent - protects sacrificially 2. Metallic Coatings - protects by exclusion but do not protect sacrificially so could accelerate corrosion once underlying metal is exposed 3. Surface Conversion Coatings - provide a reservoir of corrosion inhibitor - acts as a good base for paint

AIRCRAFT ENVIRONMENTAL DAMAGE PREVENTION AND CONTROL Why are supplementary protectives important?

Provide short and long term temporary protectives that are easily removed by solvent action and semi-permanent materials

TYPES OF CORROSION Define corrosion..

Tendency for a metal to revert to their thermodynamically more stable oxidised state

TYPES OF CORROSION Which metals are strongly resistant to corrosion?

Gold and Platinum

TYPES OF CORROSION What two types of reaction may occur between metals and their environments?

Either dry or in an aqueous environment

TYPES OF CORROSION What is the term oxidation usually describing?

The direct combination of a metal with the oxygen of the atmosphere

TYPES OF CORROSION What physical changes show oxidation in the materials below? 1. Iron/Steel 2. Aluminium Alloys 3. Magnesium Alloys

1. Red Rust 2. White to grey powdery deposits 3. Same as above however give a fluffy or granular appearance

TYPES OF CORROSION Before the specific signs, what are the early signs of corrosion?

Flakes or blisters in the paint finish

TYPES OF CORROSION What is the most usual type of corrosion? Which contaminants usually cause this?

Surface Corrosion Sea-air Aircraft exhaust gases Funnel smoke

TYPES OF CORROSION State the type of corrosion.. Frequently occurs where there is a leakage of a highly corrosive fluid, such as battery acid. Usually found on metals which have a natural oxide skin.

Pitting Corrosion

TYPES OF CORROSION State the type of corrosion… Damage is in the grain boundaries in the metal. Showed as a group of corrosion areas or cracks on the metal surface - doesn’t always occur. Gives very little, or no, external indication

Intergranular corrosion

TYPES OF CORROSION State the type of corrosion… A type of metal failure can occur and cause cracks from the internal or external structural or operational loads causing stress

Stress corrosion

TYPES OF CORROSION State the type of corrosion… Cyclic stresses from an external loads cause this type of stress corrosion. Cracks start as small pits

Fatigue Corrosion

TYPES OF CORROSION State the type of corrosion… Very small movements between two heavily loaded surfaces, one of which must be metal. Shows at an early stage as a change of the surface colour. Steel shows as a brown stain

Fretting Corrosion

TYPES OF CORROSION State the type of corrosion… Areas which are liable to preferential attacks, usually by a differential aeration form of corrosion intensified by the high ratio of cathode to anode area involved

Crevice Corrosion

TYPES OF CORROSION State the type of corrosion… Occurs beneath thin protective coatings on aluminium and steel alloys. Often starts at fasteners and extends as thread-like lines of corrosion under paint. Usually very shallows and not structurally dangerous

Filiform Corrosion

TYPES OF CORROSION State the type of corrosion… A form of intergranular corrosion in which the attack occurs in layers parallel to the surface. The wedging action causes lifting of the metal surface at an early stage when the corrosion is close to/on the surface. The further down this starts, the more detrimental it shall be

Exfoliation or Layer Corrosion

TYPES OF CORROSION What is another term for layer corrosion?

Exfoliation Corrosion

TYPES OF CORROSION How does Electrochemical Corrosion occur? IF this occurred between Zinc and Copper, which one would be the anode? Which is the cathode?

Caused by an electrolytic effect between two different metals which touch via liquid Anode: Zinc (progressively decreases in size) Cathode: Copper ( progressively increases in size)

CORROSION PRONE AREAS What are the the key watchwords for all husbandry procedures?

1. Keep aircraft CLEAN 2. Keep aircraft DRY 3. Maintain aircraft PROTECTIVE COATINGS

CORROSION PRONE AREAS List the top 7 areas prone to corrosion…

External surfaces Undercarriages Helicopter Rotating Assemblies Engine Intakes, Cooling Air Vents Electrical Equipment Exhaust Areas Cargo Floors

EROSION PREVENTION AND CONTROL What is Erosion?

Erosion is the loss of material from aircraft components by the action of small particles such as grit, sand, stones, ice and water

EROSION PREVENTION AND CONTROL State the issues which erosion causes…

Destroys component corrosion protection Introduces wear to mechanical and avionics system Degrades optical quality and strength of transparencies Affect intake and airframe aerodynamics A source of fatigue crack initiation

EROSION PREVENTION AND CONTROL What can significantly reduce the risk of erosion?

Effective use of tap Abrasion-resistant or anti-erosion paints Suitable operating procedures

EROSION PREVENTION AND CONTROL Who must authorise the specific process and materials used to protect and control against erosion?

Type Airworthiness Authority and detailed within the Aircraft Document Set

MAINTENANCE IN EXTREME ENVIROMENTS What are the two extreme environments?

Artic Conditions High Temperature environments

MAINTENANCE IN EXTREME ENVIRONMENTS List the three high temperature environments..

Desert Arid Salt Laden Hot and Humid

MAINTENANCE IN EXTREME ENVIRONMENTS What are the three major consequences of corrosion?

1. Reduction in static strength 2. Stress corrosion cracking 3. Shortening of fatigue life

DISCOVERING AND RECTIFYING CORROSION What are the two types of ways corrosion can be removed?

Mechanical and Chemical

DISCOVERING AND RECTIFYING CORROSION What mechanical methods are used to remove corrosion?

Grinding with abrasive wheels Manual grinding Abrasive blasting using a Vacu-Blast

DISCOVERING AND RECTIFYING CORROSION State 3 essential requirements when removing corrosion..

Remove all corrosion, hidden and visible Leave surface smooth Leave surface uncontaminated by the removal process Do not blend material into a crack Do not exceed any metal removal limits that may apply

DISCOVERING AND RECTIFYING CORROSION What materials usually require chemical removal of corrosion products?

Aluminium and magnesium alloys

DISCOVERING AND RECTIFYING CORROSION Where is chemical removal methods potentially dangerous?

Where residues cannot be completely removes eg crevices, laps and enclosed areas

RESTORATION OF PROTECTIVE FINISH Why do we use Pre-treatment?

To provide protection and give a suitable base for the adhesion of the primer

REMOVAL AND NEUTRALISING CORROSIVE AGENTS What should be used to clean up in the event of a acid spillage?

Use a clean rag to soak up as much as possible Neutralise the area with an aqueous solution of 10% by weight of sodium carbonate

REMOVAL AND NEUTRALISING CORROSIVE AGENTS How do you know when cleaning is adequate?

Universal paper will give a PH value between 5 and 9 Paying close attention to to positions where the spill could be trapped

REMOVAL AND NEUTRALISING CORROSIVE AGENTS How often after a acid or alkali spill should the aircraft be reexamined?

Re-examine the area at weekly intervals If there is no contamination in the first week, still re-examine a week later

REMOVAL AND NEUTRALISING CORROSIVE AGENTS What actions should be took after an alkali spill?

Use a clean rag to help soak up the spillage Use a 5% (by weight) solution of chromic acid in water

REMOVAL AND NEUTRALISING CORROSIVE AGENTS What should be noted when using chromic acid?

Chromic acid is poisonous an corrosive t some metals at high concentration. Rags contaminated are at fire risk and should be disposed of as industrial waste

REMOVAL AND NEUTRALISING CORROSIVE AGENTS How should micro-organisms be removed?

Removed with a bristle brush and a solution of one part (by volume) of cleaning compound and five-parts hot water at about 50 degrees. Area must be rinsed with copious quantities of clean water

REMOVAL AND NEUTRALISING CORROSIVE AGENTS After removal of micro-organisms, what areas should be carefully inspected for remaining contamination and corrosion?

Tank surfaces and plumbing