Module 6a

Knowledge Levels

• Categories A, B1, B2 aircraft maintenance licenses require basic knowledge, indicated by levels 1, 2, or 3 for each subject
• Category C applicants must meet either B1 or B2 basic knowledge levels

Level 1

• The applicant should be familiar with the subject's basic elements
• The applicant should be able to describe the subject simply, using common language and examples
• The applicant should be able to use typical terms

Level 2

• Requires general knowledge of the theoretical and practical aspects of the subject, and the ability to apply that knowledge
• The applicant should understand the subject’s theoretical fundamentals
• The applicant should be able to give general descriptions using typical examples
• The applicant should be able to use mathematical formulas with physical laws
• The applicant should be able to read and understand sketches, drawings, and schematics
• The applicant should be able to apply their knowledge practically using detailed procedures

Level 3

• Requires detailed knowledge of the theoretical and practical aspects of the subject
• Requires the capacity to combine and apply separate elements of knowledge logically
• The applicant should know the theory of the subject and interrelationships with other subjects
• The applicant should be able to give detailed descriptions using theoretical fundamentals and specific examples
• The applicant should understand and be able to use mathematical formulas
• The applicant should be able to read, understand and prepare sketches, simple drawings, and schematics
• The applicant should be able to apply their knowledge practically using manufacturer's instructions
• The applicant should be able to interpret results from various sources/measurements and apply corrective action

Aircraft Materials - Ferrous

• The learning objectives include describing the characteristics and properties of common alloy steels, identifying common alloy steels, describing the heat treatment of alloy steels, and describing the application of alloy steels

Metal Alloy Steels

• Metal characteristics identify a feature or quality of a material
• When using metal in manufacturing, metal characteristics determine where and how the metal can be used; these characteristics include strength, hardness, malleability, ductility, brittleness, conductivity, expansion, elasticity, toughness, fusibility, and density
• Metal property identifies an attribute, quality, or characteristic of a metal
• Alloying involves adding small amounts of other materials; dramatically changes the properties of the material characteristics; for example, adding carbon to steel increases the hardness of the core material

Strength

• The amount of strength that a metal possesses helps to classify it
• Strength depends on the percentages of the parent metal and other elements used to make an alloy
• There are many different types of strength, including tensile strength, compressive strength, shear strength, torsional strength, bending strength, fatigue strength, and impact strength (also known as toughness)

Metal Loading Forces

• Each strength type shows how the metal reacts to a specific kind of loading
• Tensile strength is the ability of sheet metal to withstand stress in tension
• Tensile strength includes Yield strength (the stress at which material strain changes from elastic to plastic deformation, causing permanent deformation)
• Tensile strength includes Ultimate strength (the maximum stress a material can withstand when subjected to tension, compression, or shearing; the maximum stress on the stress-strain curve)
• Tensile strength Breaking strength (the stress coordinate on the stress-strain curve at rupture)
• Compressive strength is a metal's ability to withstand being pressed or squeezed
• Shear strength is a metal's ability to withstand shear stress
• Torsional strength is a metal's ability to resist rotational shear
• Bending strength is a metal's bending strength
• Fatigue or endurance strength measures a metal's ability to resist repeated loading
• Impact strength (toughness) is a metal's ability to resist shock

Hardness

• Hardness is a metal's ability to resist cutting, penetration, or abrasion
• The tensile strength of steel relates directly to its hardness
• Some metals harden through heat treating or work hardening
• Other metals are softened through annealing

Malleability

• Malleability is a material's ability to be bent, formed, or shaped without cracking or breaking To increase malleability, metals are annealed, or softened, to form complex shapes, then heat-treated after forming to increase strength
• A malleable metal can be hammered, pressed, or rolled into thin sheets without breaking

Ductility

• Ductility is the ability of metal to be drawn into wire stock, extrusions, or rods
• Ductile metals are preferred for aircraft parts due to their ease of forming and resistance to failure under shock loads

Brittleness

• Brittleness is a material's tendency to break or shatter when exposed to stress, and is the opposite of ductility and malleability
• A brittle metal may break or crack before changing shape
• Structural metals deal with shock loads, so brittleness is not a desirable property
• Examples of brittle ferrous metals are cast iron and very hard steel

Elasticity

• Elasticity is a metal's tendency to return to its original shape after normal stretching and bending
• The flexibility of spring steel used for landing gear is an example of elasticity
• Aircraft skins' expansion/contraction when pressurized indicates elasticity
• A metal's elastic limit is the point beyond which the metal will not return to its original shape after a deforming force is removed
• Some non-ferrous metals have very low elastic limits, while hard spring steel's elastic limit is very high

Toughness

• Toughness is a material's capacity to withstand tearing or breaking when bent or stretched
• Examples of tough metals include hammer faces and wrenches

Conductivity

• Conductivity is the property that enables a metal to carry heat or electricity; thermal conductivity indicates a metal can transmit heat
• Heat exchange is metal’s ability to conduct heat away after absorbing it from a source
• Metals that carry heat also carry electrons, making them good electrical conductors
• Electrical conductivity is the measure of a material's ability to allow electron flow; metal conductors include wire, aircraft frames, and engines

Thermal Expansion

• The ability of a metal to expand when heated and contract when cooled is called thermal expansion The amount of expansion or contraction is predictable at specific temperatures, and is called its coefficient of expansion
• All aircraft experience thermal expansion and contraction as the ambient temperature changes

Fusibility

• The ability of metal to be joined by heating and melting is called fusibility
• To fuse metal means melting two or more compatible pieces of metal into one continuous part, also called fusion joining or welding

Ferrous Metals

• Any alloy containing iron as its chief constituent is called a ferrous metal, such as steel, cast iron, and titanium, as well as alloys of iron with other metals like stainless steel
• Steel, an alloy of iron with a controlled amount of carbon added, is the most common ferrous metal in aircraft structures

Iron (Ferrite)

• Iron is fairly soft, malleable, and ductile in its pure form; it is a silvery white and heavy chemical element
• Iron combines with oxygen to form iron oxide, or rust
• Iron is mixed with various forms of carbon and other alloying agents or impurities
• Cast iron is iron poured from a furnace into moulds, normally containing over 2% carbon and silicon
• Cast iron has few aircraft applications because of its low strength-to-weight ratio
• Cast iron is used in engines for items such as valve guides, where its porosity and wear characteristics allow a lubricant film, and in piston rings

Steel Composition

• Steel is a material primarily made of iron
• Carbon is the second element in all types of steel, but iron and carbon are the only elements found in all steel
• The carbon content primarily makes the difference between steel, cast iron and wrought iron

Identification of Steels

• The Society of Automotive Engineers (SAE) uses a 4-digit numerical index to represent chemical composition standards for steel specifications
• The 1st digit identifies the principal alloying element
• The 2nd digit indicates the percentage of the principal alloying element
• The last two digits indicate the average carbon content in hundredths of a percent

SAE Steel Numbering System

• 1xxx signifies carbon steels
• 2xxx signifies nickel steels
• 3xxx signifies nickel-chromium steels
• 4xxx signifies molybdenum steels
• 5xxx signifies chromium steels
• 6xxx signifies chromium-vanadium steels
• 7xxx signifies tungsten steels
• 8xxx signifies nickel-chromium-molybdenum steels
• 9xxx signifies silicon-manganese steels

Alloying Agents in Steel

• Pure iron has few practical uses, but small amounts of other materials added change its properties dramatically; common alloying agents include carbon, sulfur, silicon, phosphorus, nickel, and chromium.

Purpose of Ferrous Metal Alloys

• Adding small amounts of other materials to iron can dramatically change it's properties

Carbon

• Carbon is the most common alloying element in steel
• Compunds of iron carbides called cementite can form when mixing carbon with iron
• The carbon allows the steel to be heat-treated to obtain varying degrees of hardness, strength and toughness
• The greater the carbon content, the receptive steel is to heat treatment, and increases its tensile strength and hardness.

Carbon content effects

• Higher carbon content decreases malleability and weldability
• A letter after the alloy designation indicates metal hardness or temper with a dash

Low-carbon or mild steel

• Low-carbon or mild steel is primarily used in non-structural areas, but used to utilized in steel-tube construction
• Low-carbon or mild steel is easily welded and machined readily, but does not heat treat

Medium-carbon steels

• Medium-carbon steel will accept heat treatment; is adaptable to machining or forging; and is used when surface hardness is desirable

High-carbon steels

• High-carbon steel is very hart; used in springs, files, and some cutting tools

Other Alloying Agents

Silicon

• Silicon acts as a hardener when alloyed with steel; Small quantities also improve ductility

Manganese

• Mangalloy is a unique non-magnetic steel with extreme anti-wear properties; it is abrasion resistant and achieves up to three times its surface hardness during conditions of impact, without any increase in brittleness

Sulphur

• Sulphur is typically an undesirable impurity in steel
• Sulphur causes steel to be brittle when rolled or forged, and therefore must be removed in the refining process; if sulphur cannot be removed, manganese can be added to counter sulphur and other oxides

Phosphorous

• Improves the yield strength of steel and the low-carbon steel's resistance to atmospheric corrosion

Nickel

• Adds strength and hardness to steel and increase its yield strength
• Nickel slows the rate of hardening when steel is heat-treated, increases hardening depth, and produces a finer grain structure, which reduces steel’s tendency to warp and scale when heat-treated.

Chromium

• Chromium increases strength and hardness, as well as improve wear and corrosion resistance
• Applications include the balls and rollers of antifriction bearings
• Used to electrolytically deposit on cylinder walls/bearing journals to provide a hard, wear-resistant surface

Nickel-Chromium Steel

• Nickel toughens steel, and chromium hardens it; when alloyed, the steel gains desirable strength for high-strength structural applications

Molybdenum

• One of the most widely used alloying elements for aircraft structural steel; reduces the grain size and increases its impact strength and elastic limit
• Molybdenum steels are extremely wear-resistant with great fatigue strength
• Chrome-molybdenum steel is easily welded by gas or electric arc, and responds well to heat treatment; the steel is a good choice for landing gear structures and engine mounts.

Vanadium

• When combined with chromium, vanadium produces a strong, tough, ductile steel alloy
• Ball bearings are made of chrome-vanadium steel

Tungsten

• Has an extremely high melting point and adds this characteristic to steel it is alloyed with; because tungsten steels have high density (high mass) and retain their harness elevated operating temperatures, they are typically used for control surface balance weights and breaker contacts in the magnetos

Titanium

• Titanium alloys have high tensile strength and toughness (even @ high temperatures)
• Lightweight with high corrosion resistance

Stainless Steel

• Corrosion-resistant steels that contain large amounts of chromium and nickel, making them well suited for high-temperature applications such as firewalls and exhaust system components

Heat Treatment of Steel

• As mentioned before, pure iron isn't suited for structural material due to being weak, soft, very ductile and unresponsive to heat treatment
• Steel is typically iron alloyed with carbon and a percent of alloying elements, can all be heat treated to a high degree of strengths, taughnesses and ductilities

Purpose of Steel Heat Treatment

• Steel heat treatment changes physical and mechanical material properties of carbon steel through heating and cooling without changing size or original shape
• Heat treatment is often associated with strengthening steel, but also improves machinability or formability, and restore ductility
• High carbon steels are well fit for heat treatment

Annealing

• Annealing softens steel and relieves internal stress
• Annealing involves heating steel, soaking it at a specified temperature and cooling
• Cooling is done leaving it in the furnace, packing the steel in hot ash/sand for heat conduction

Normalising

• Normalizing reduces stresses, particularly in ferrous metals used in high-stress operations
• It involves heating steel, maintaining the temperature until uniformly heat-soaked, and cooling it in still air
• This allow particles of carbon to precipitate out, but are not of annealed quantities
• Highly effective for welds.

Hardening

• Carbon steel can be hardened readily, the maximum obtained hardness depends on carbon content
• To harden steel, heat it so carbon can disperse; then, cool it rapidly by quenching it in water, oil, or brine (water with a high salt content); quench speed depends on the medium

Tempering

• With Tempering, lessens unwanted qualities from steel's brittleness
• Heating an alloy to a specific temperature so it becomes heat then allowing the metal to cool naturally in room temperature air
• Tempering softens from hardness and brittleness and improves steel's ductility and toughness

Case Hardening

• A hardening proccess for aircraft components like gears and bearings
• It requires metal with hard, durable surface and core material that remains
• Is accomplished through an ideal and simplified process known as case hardening; a fitting proccess for low carbon steel

Aircraft Materials - Non-Ferrous Materials

• The learning objectives include describing the characteristics and properties of common non-ferrous materials, identifying common non-ferrous materials, describing the heat treatment of non-ferrous materials, and describing the application of non-ferrous materials

Properties of Non-Ferrous Metals

• Metals without iron indicate being non-ferrous
• Aluminium, copper, titanium, and magnesium represent the most common non-ferrous metal

Identifying Aluminium

• Pure aluminium lacks the strength needed for construction, but increases in strength when alloyed or mixed with compatible metals
• It possess resistance to corrosion and carries over to it

Alloying Elements

• Aluminium alloys are classified by their major alloying ingredient such as:
• Copper, Magnisium, Manganes and Zinc

Main Classes of Aluminium Alloys

• Wrought Alloys are rolled from an ingot or extruded from custom shapes
• Cast Alloys, poured as a liquid into mould and cooled into a solid shape.

Wrought Aluminium Alloys Designation System

• Four digit index system identifies wrought aluminium alloys

Alloy Series

• 1xxx has a principle alloying element with minimum of 99.00% Aluminum content
• 2xxx has copper for it's principle alloying element
• 3xxx has manganese for it's principle alloying element
• 4xxx Silicon for principle alloying element
• 5xxx Magnesium for principle alloying element
• 6xxx Magnesium and Silicon for principle alloying element,
• 7xxx Zinc for principle alloying element
• 8xxx other elements for principle alloying element,
• 9xxx unused series

1xxx Series of Alloys

• Is made of pure aluminium
• Posses the following features: Strain-hardenable, high formability, corrosion resistance and electrical conductivity, and Electrical, chemical applications

Aluminium/copper 2xxx Series

• Alters certain metallically grain structures, when altered are beneficial to greater strength
• Major drawback is susceptibility to intergranular corrosion when improperly heat treated
• Some of the alloys used in aircraft are rivets being 2017 and 2024.

3xxx is the series with manganese as its alloying element

• It displays moderate strength with good working characteristics, and is generally considered non-heat-treatable

Heat Treatment

• It is series with aluminium is alloyed with silicon, which lowers a metal's melting temperature, and works well for welding or brazing.

It is the 5xxx Alloy Series

• Magnesium alloy is very good with resistance to welding, corrosion , and the metals may be exposed to high temperatures

The 6xxx series designation

• Has medium strength that has resistant properties because the result is a carrying of silicon and magnesium is added

More Strength

• It takes little forming, harder aluminium alloys are employed 7xxx Series
• Addition zinc makes alloy stronger and harder
• Widely used forms are aluminium-zinc alloys are 7178 and 7075.

An example on a medium-sized passenger aircraft:

• Aluminum alloy 7075 ( aluminum/ zinc ) is formed from frames and stringers, floor beams and wing ribs - Has resistant High mechanical properties and improved stress corrosion cracking.

• In order to minimize residual heat treatments the bulkheads, frames and window and landing gear beam are made from Aluminum Alloy 7079 (zinc aluminum)

• High compressive strength, the upper skin, spars and beams of the wing is made from Aluminium alloy 7178 (zinc/aluminium, magnesium, copper)

• Landing gear is made from alloy 7175 (Aluminium, zinc magnesium copper with extreme tough to handle use and tensile strength alloy

• High tensile skin is made from Aluminum alloy 705 (magnesium, zinc, copper) by use to give corrosion Superior stress

• Where greater strength is needed combined with an increases in high stiffness, aerospace applications alloys need to increased stiffness then the 8xxx Provides reduced component weight .

• The 8xxx Series provides exceptionally high strength and elasticity Aluminium 8xxx alloys provides the fractured surfaces of 8090 Al-Li alloy The 9xxx Series alloys are unassigned at this time.

Clad Aluminium Alloy (Alclad)

• Alclad aluminium that possesses most external of corrosion resistance and made from sheets used for air craft.
• is rolled onto surface are clad and pure with aluminium alloys of both and heat treated .

Heat of Aluminium Alloys of Treatment:

• Aluminum alloys Heat Treatment refers to a metal or solid in a series of operations when cooled or heated.

Some properties can improve

• A the price of metals others such as becoming brittle, and a single, one may not can produce operations.
• Metals can be similar when involving two or more cooing when heating however rate to which metail is Heated to be with they differ.

Treatment types

• Solution heating/treatment and heating/precipitation Treatment

Solution Heat Treatment

• Procedure in this Certain aluminium is heated in order then element an is allowed to mix to the metal that to a furnace in molten either bath or with the sodium to either before or just potassium in Nitrate point, maintaining metal temperature

Treatment

• During then temperature is soaked and held for an uniform throughout with the element alloying metal base..

Heat-treating - allows

• Remove the temperature is an specified for the metal to leave it is important remove that sufficiently to the element.

For example

• That precipitates metal to then becomes grains out from to is not a bath medium to ensure alloys aluminium provides sheet.
• In immediately straightening quench sodium thin nitrate rinsing then or aluminium is quenched it. salt the from or
• Corrosion lead then, to the if corrosion in to to the nitrate can metal the

Naturally/Precipitation Heat Treatment

• Alloys aluminum derive strength with this and are resistance, process together, develop by hardness, strength, and this, and the locking alloy
• The strength then the no relatively short is time however.
• A treatment heat further require not alloys need zinc, contain those higher treat of these alloys.
• Temperatures - aluminum aged alloys that by alloys derive need treatment heat longer by

Treatment Reheat

• Treat-heat may be time heat material if such Drive.
• The Cladding decreases more corrosion is the limits treatment Heat

Non-heat-treatable Aluminium

• To by rolling or work cold these. in therefore, alloys' aluminium treat non heat.

To improve in to cold hard work:

• Alloys aluminium -treatable heat and treat-heat non Both it
• The pressing or metal can also the hardens grain and requires strength

###Designates of Hardness

Designate and define letter with is -designation or a appropriate, are

Followed

• One or More:
• Hardened & strain, is 8 an an the and hardened, stabilised, has material, H38, example, for The the example, strength
• That is the state.

6.28 Types of Alloy

Used by Types of Other - By magnesium air in powder, exercised sand is dry

• The Oxygen (High)
• Oxygen exclusion.
• Heated cracked . * Material thin hot dipping.
• Burn Dust. For precautions the