Metal Alloy Steel Properties

Knowledge Levels

• Basic familiarity is level 1.
• General knowledge of theory and practice is level 2.
• Detailed theory and practice is level 3.

Metal Alloy Steels

• Metal "characteristics" identify features of a material.
• Characteristics determine how a metal is used in manufacturing and construction.
• They include strength, hardness, malleability, ductility, brittleness, conductivity, expansion, elasticity, toughness, fusibility, and density.
• "Metal property" identifies an attribute of a metal.
• Alloying changes material characteristics dramatically.
• Adding carbon to steel increases its core hardness.

Strength

• The amount of strength metal possess is determined by the percentages of the parent metal and other elements used to make an alloy.
• Types of strength: tensile, compressive, shear, torsional, bending, fatigue, and impact.

Metal Loading Forces

• Each type of strength is how a metal reacts to a specific type of loading.
• Tensile strength enables sheet metal to withstand tension.
• Yield strength is stress where material strain changes from elastic to plastic deformation, causing permanent deformation.
• Ultimate strength is the stress capacity a material can withstand when subjected to tension, compression, or shearing. It's the maximum stress on the stress-strain curve.
• Breaking strength is the stress coordinate at the point of rupture on the stress-strain curve.
• Remaining fundamental loading forces include compressive, shear, and torsional strength and bending strength.
• Fatigue strength (or endurance strength) is a metal's resistance to repeated loading.
• Impact strength (toughness) is a metal's ability to resist shock.

Hardness and Malleability

• Hardness measures a metal's resistance to cutting, penetration, or abrasion.
• Tensile strength in steel relates directly to hardness, though the relationship isn't absolute for all metals.
• Some metals are hardened via heat-treating or work hardening, while others are softened by annealing.
• Malleability describes a material's ability to be bent, formed, or shaped without cracking.
• Hardness and malleability are considered opposite properties.
• To increase malleability, metals are annealed.
• Malleable metal can be hammered, pressed, or rolled into sheets without breaking.
• Highly ductile metal is malleable, and non-malleable metal is brittle.

Ductility, Brittleness, Elasticity

• Ductility measures a metal's ability to be drawn into wire stock, extrusions, or rods.
• Ductile metals are preferred for aircraft use due to easy forming and resistance to failure under shock loads.
• Brittleness is a material's tendency to break or shatter when exposed to stress and opposes ductility and malleability.
• Brittle metal is more prone to breaking or cracking before shape change.
• Structural metals tend to resist shock loads, so brittleness is not desirable.
• Cast iron and very hard steel are examples of brittle ferrous metals.
• Elasticity measures a metal's tendency to return to its original shape after normal stretching and bending.
• Spring steel used in landing gear is an example of elasticity.
• Aircraft skins expand and contract when pressurized, demonstrating elasticity.
• A metal's elastic limit is the point beyond which it won't return to its original shape after deformation.
• Certain non-ferrous metals have very low elastic limits, while hard spring steel's elastic limit is high.

Toughness, Conductivity, and Expansion

• Toughness measures a material's ability to resist tearing or breaking when bent or stretched. Hammer faces and wrenches require toughness.
• Conductivity measures a metal's ability to carry heat or electricity; thermally conductive metals transmit heat.
• Conductivity to carry heat away is called heat exchange and an example is the fins on air-cooled piston cylinder heads.
• Electrically conductive metals carry electrons and metal conductors include wires, aircraft frames or engines.
• Thermal expansion measures the ability of a metal to expand when heated and shrink when cooled.
• Thermal expansion/contraction is predictable at specific temperatures and measured by its coefficient of expansion.
• Aircraft experience thermal expansion and contraction as ambient temperatures change.

Fusibility

• Fusibility measures the ability of metal to be joined by heating and melting; metal fuses to melt pieces into a continuous part.
• Fusion joining, also called welding, melts two or more compatible pieces of metal into one part.

Ferrous Metals and Steel

• An alloy with iron as its main component is a ferrous metal; examples include steel, cast iron, and titanium.
• Steel is the most common ferrous metal in aircraft structures and is an alloy of iron with carbon.
• Iron is soft, malleable, ductile, and silvery white in its pure form, combining with oxygen to form rust and alloying with carbon and other agents.
• Cast iron contains greater than 2% carbon and some silicon with limited aircraft use due to its low strength-to-weight ratio.
• Steel is material composed primarily of iron and all steels contain carbon.
• Differences between steel, cast iron and wrought iron relate to carbon content.

Steel Identification

• The Society of Automotive Engineers (SAE) uses a 4 digit numerical index system for steel chemical compositions.
• The first digit identifies the principal alloying element; the second indicates its percentage.
• The last two digits mark the average carbon content in hundredths of a percent.
• SAE designations:
  • 1xxx – Carbon steels
  • 2xxx – Nickel steels
  • 3xxx – Nickel-chromium steels
  • 4xxx – Molybdenum steels
  • 5xxx – Chromium steels
  • 6xxx – Chromium-vanadium steels
  • 7xxx – Tungsten steels
  • 8xxx – Nickel-chromium-molybdenum steels
  • 9xxx – Silicon-manganese steels.

Alloying Agents in Steel

• Pure iron has few practical uses, with alloying agents changing its properties; common agents include carbon, sulphur, silicon, phosphorous, nickel, and chromium.
• Carbon is the most common alloying element in steel.
• Iron carbides known as cementite form when mixed with iron.
• Carbon addition enables heat-treating to vary hardness, strength and toughness.
• The higher the carbon content, the higher the tensile strength and hardness, but weldability and malleability is decreased.
• Temper is indicated by a letter set off by a dash.

Low, Medium, and High-Carbon Steels

• Low-carbon or mild steel: primarily used in non-structural settings, is easily welded and machined, and doesn't accept heat treatment.
• Medium-carbon steel: accepts heat treatment, is easy to machine and forge, and used where surface hardness is desired.
• High-carbon steel: very hard, used in springs, files and cutting tools.
• With silicon: It acts as a hardener, improving ductility and manganese is extreme anti-wear, resists abrasion, and can reach 3x surface hardness under impact.
• Sulphur added in small amounts improved machinability. Sulphur should be removed if possible, during refining or can be countered using manganese which combines with the sulphur to form managanese sulphide.
• Phosphorous improves low-carbon steel's yield strength and resistance to atmospheric corrosion.
• Nickel adds strength and hardness, increases yield strength, slows hardening during heat treatment, increasing hardening depth and produces finer grain.
• Chromium increases strength and hardness, improves wear and corrosion resistance, used in balls and rollers of antifriction bearings.
• It is also electrolytically deposited on cylinder walls/bearing journals providing hard, wear-resistant surface.
• Nickel/chromium: nickel toughens and chromium hardens steel providing high-strength structural applications.
• Molybdenum: is a widely used in structural steel, reduces grain size, increases impact strength/elastic limit, and it is wear resistant with good fatigue strength.
• Chrome-moly steel machines readily, welds easily, responds well to heat and is a top choice structural use.
• Vanadium: combined with chromium produces strong, tough, ductile steel used in ball bearings.
• Tungsten raises the melting point, so it is alloyed with to retain hardness at high operating temperatures.
• Tungsten steels are typically used for control surface balance weights and breaker contacts in magnetos due to its high density.
• Titanium steel alloys: have high tensile strength/toughness and are lightweight with corrosion resistance and withstand extreme temperatures.

Stainless Steel and Heat Treatment

• Stainless steel classifies as corrosion-resistant steel with chromium and nickel best suited for high-temperature applications like firewalls and exhaust systems.
• Pure iron is not suitable as a structural material because it is weak, soft, and unresponsive to heat treatment.
• Steel alloyed with carbon and other elements can be heat-treated to achieve a range of mechanical properties.
• Carbon is the most important alloying element for controlling steel properties.
• Heat treatment is the process of heating and cooling carbon steel to alter its physical and mechanical properties without changing its original shape or size.
• It can increase strength and modify manufacturability, improving machinability or formability and is most effective for high-carbon steel.

Heat Treatment Processes

• Annealing softens steel, relieves internal stress, heats/soaks/cools it in the furnace or by packing.
• Normalising relieves stresses, heats/maintains temperature until uniformly heated, then cools in still air good on welded parts.
• Hardening heats steel until carbon disperses uniformly, cools rapidly by quenching in water, oil, or brine with oil providing the slowest quench, brine the fastest.
• Tempering reduces brittleness and heats alloy to heat-soaked temperature, then cools in room temperature air or in still air reducing hardness and brittleness and improves ductility/toughness.
• Case hardening is for parts like bearings/gears needing hard, durable surfaces with tough core material on the low steel is best suited.

Non-Ferrous Aircraft Materials

• Aluminium, copper, titanium and magnesium alloys are some of the more common non-ferrous (no iron) metals used in aircraft construction and repair.
• Pure aluminium alone lacks structural strength. Its strength can be increased when alloyed with Cu or other metals. The resultant alloy can be as strong as steel yet it can be made much lighter.

Wrought Aluminium Alloys 1xxx-4xxx

• 1xxx series is made of pure aluminium; features strain-hardenable, high formability, corrosion resistance and electrical conductivity.
• 2xxx series alloys that contain copper can undergo changes in grain structure and they have greater strength, their susceptibility to intergranular corrosion is a drawback.
• Aluminum-copper is alloy used in construction of skins and rivets are 2017 and 2024.
• 3xxx Series use manganese as the alloying element; considered non-heat-treatable and offer moderate strength with good working characteristics.
• 4xxx Series aluminium is alloyed with silicon to lower its melting temperature, working well for welding and brazing.

Wrought Aluminium Alloys 5xxx-9xxx

• 5xxx Series uses magnesium, that possess good welding/corrosion-resistance, but may see susceptibility to corrosion if exposed.
• If Al is mixed with silicon and magnesium will use a 6xxx Series with med strength with good forming and corrosion.
• 7xxx Series alloys are made harder/stronger by addition of zinc with aluminum-zinc alloys 7075 and 7178.
• Key frames, stringers, keel and floor beams, and wing ribs made of aircraft frames use of aluminium alloy 7075
• Bulkheads, window frames, and landing gear beam of plane is of aluminium alloy 7079
• Wing upper skin, and main structural components are made of aluminium alloy 7178.
• The gear beam made of aluminium alloy 7175 providing a high tensile strength alloy.
• The wing's lower skin is comprised of aluminium alloy 7055 for good corrosion resistance.
• 8xxx Series provides exceptionally high elasticity, so this alloy is used for aerospace applications where an increases in stiffness combined with high strength reduces component weight.
• 9xxx Series alloys are currently unassigned.

Other Aluminium Considerations

• Alclad is a pure aluminium coating rolled onto heat-treated aluminium alloy sheets so corrosive agents can't attack the alloy.
• Pure Al coating provides the corrosion protection to the alloy underneath. If clad is scratched then that spot is prone to corrosion.
• Heat Treatment of Al involves heating and cooling the metal in its solid state. It changes the service use of the metal.
• To help with serviceability and prevent the material from becoming brittle during the hardening process.

Heat Treatment for Aluminium

• Solution heat-treating heats aluminums to mix alloying elements, so the metal is heated in molten nitrate or in air furnace.
• Once ready, the removal of the alloy the cooling process happens in seconds, as process is Alloy metals precipitate of base.
• A quenching medium is selected to ensure equal cooling rate of Al alloy.
• The alloy is selected is based on the correct cooling rate by having the proper Aluminium alloy.
• Precipitation heat treatment: Heat-treatable aluminum alloys comparatively soft and needs to harden, alloy naturally, and can take weeks.
• However Al becomes strong alloy. at room temp, known natural change for examples, aluminium alloyed gains about 90% in 30 Mins.
• Aging is the speeding or slowing down the processes for some metals/ alloys.

Aluminium Alloy Composition and Annealing

• In non Heat treatable Aluminum are designated in the the 1000, 3000, 4000, 5000 Series. They all are adjusted by cold work.
• When appropriate a metals hardness or temper is separated from the alloy with a dash/letter designation and is indicated the degree of the strain.
• Anneling process that softens metal and decreases stress, General is that it's opposite to hardening. To anneal Al, temp raised until heat-soaked.
• Clad Al should be heated carefully and quickly so excess heat of the core with cladding is reduced along with the corrosion resistance.

Aluminium Alloy Temper and Alloys

• Heat-treatable alloys have hardness condition that is designated by following the latter "T" followed numbers.
• Solution, Heat-treated (T): different amounts of hardening are indicated by a second digit (T3).
• T4 is heated to a Stable condition, after being cool. artificially aged after rapidly after its extrusion (T5).
• T6 is the solution heat that follows the artificial aging.
• Material which been heated before can generally treated several, such with making rivets by allowing 2017/2024 alloys being super hard.
• But by making them soft they can make them useable.
• Solution heat treatment allowed for clad materials limited due to increase the diffusion of the core to the cladding.
• Wrought Form available like in Sheets and tubing extrusions. The magnesium alloy can vary.

Other Alloys

• They very light but high susceptibility to corrosion so needs protect with chemicals. Cracking, this can be avoided by heating parts.
• Readiness to burn in small form, so cautiion using. The solution increase the tensile strength, elasticity, and resistance to shock.
• Titanium is lightweight and hight strength all but sensitive nitrogen & oxygen, It can be converted before doing work.
• It can used civilian planes while being used extensively. Also there is Nickel element its the more commonly used form such with Monel ,Inconel.

Monel and Inconel

• Monel contains nickel, copper, small amounts of iron and magnesium.
• Strong, good machining, and the high % of Al heat treat tensile test of steel . This be used for gears where strength is needed , and high temp environment.
• The inconel alloys contain nickel along chromine + small iron .These be the engines ability corrosion resistance. Example: supports/Blades.
• Copper alloys are copper w tin, brass and bronze; these find little construction application . For wiring copper is is used.

Aircraft materials testing

• Metallic testing is ensuring the qualities have been achieved. Hardness is first tested for. Tensile also check fatigue, and impact-resistance. -Testing is on a piece of materiel with same as the aircraft part also. -Hardness testing: strength has hardness and requires measuring Brinell has tested, uses spherical penetrator.
• While load is being applied the hand pump is read along a presser gauge.
• And the diameter is by a microscope with scale of the impression.
• The Rockwell hardness tester measure the material its sinking which is the same to Brinell. The dial indicates the metal sinking.

Airframe and Composites

• Rockwell uses 3 types, they be applied using three heads.
• The strength to load measured of testing. It done my applying load while getting.
• Applying tensile by the elongations to its graph.
• Fatigue testing establish is a level the will occur with structural test. Special shaped peace gripped and using overhung for the testing.
• Airframe test is is given key design to help identify causes, and damage wear to structure. Testing helping with maintenance programs.
• Impact resistance has charpy/ Izcd is help measuring.
• It involves having mechanical test.

CVN Testing

• The Charpy V-notch (CVN) is the most common to metals.
• The metal cut squared the weighted pendulum with a knife the specimen The pendulum which goes rise after impact and you calculated.

Composite Materials

• How they evolve, their features.
• Composite: more or equal to 2 with this stronger structure. Excellent in properties strength and sent to change. This required approach
• Design is quality control and has greater strength to wight ratio. It does allow complex contoured allowing reducing drag. Composition depends or types and and use part with stand stresses.
• Fibe: The part has fibre, metric matrix, and between interface boundary.

Composite Fabric

• Fabric is important construction for design, and must be understand, unlike Metallic it relays the proper the reinforcing, Term used can be fiber, bias.
• Warped: and has warp direrecinon desinacted, fibre, it is critical,
• Weft: Fill are used at the fabrics perpical the worn fibre the weave together it reinforcing.
• Selvage Edge is parallel to the weave which stops the unravelling its removes to to body of fabric it having strength Bias: This is the fiber 45 deg angle allows manipulators.

Unidirectional, multidirectional Fibers and Fabrics

• Unierctional. Giving the fiber direction. giving much fibre its length it not woven. The little have the major fibers
• Multi: fibers that use that 2 or more. More stronger the warp Fabrics are weave into number of style weight. Woven are fiber from damage. there come weaves Weavers, Satin weave, will.

Types of Fabrics and Composites

• Weaves in one or more
• Plain weave: In in this fill and warp are interlaces such with stability and low yarn slippage.
• Satin weave: The Weave is floats with in smoothness which the surface and the warp floats.
• Tempering: Twill is weaves that many time and variations. It is for composite high aircraft, planin weave used in high air craft.

Compsite Boling, Matrix, and Resin

• Marine is joining material surrounding extra strength. Strength lies in resin transferring stress. Advanced composite various newer.
• Matrix system are type plastic. It refer as fibroo. There two general categories: These resins use in structural like high-string or composites also.
• -- Thermoplastic.
• Thermosetting. .

Resins

Thermo plastic are used for form with heat for shape not permanent. If second use heat its can be use Thermo plastic can be identified has trade. . Acrylic is stiffer thinner in airframe .

• Thermosetting: Its more that, high airframe apicabilies. Polyester Epoxy.
• Polyester resin. And be use composite like such with trim while strong, its can have a high lack the rigidity.
• The is used for chemical and be accelerated heat within. And the less has the heat in the the faster process cures.
• The a lot layers cures more before submitted thin layer,. Warning never with Catalysis has they're mix with explode to   be the 2.
• Resin with high viscosity to easily fibers the use of correct amount in it proper
• All, Resin by 2 parts.

Bonding Sealant

• Other are bonding used in resin. Others been known by the parts of glue together These, resin catalyst can mix different. With all for being a blend by film by with plastic or refrigeration for, lowing cure rate which to the permanent. adhesive
• Adhesive's using patch to be area. Is used splice replacement, this is heat use foam that add into crevies.
• Sealents Is in many engine aircraft system some app are O .The is rotate before torque the has stresses.

Composites for Aircraft

Thermography is also to identify which structures and moisture ingress as post flight. The damage done from a high speed, then the plane is being is graded has such: Damage or impact the can do on it, the damage and do by procedure and with the limits. Repairable the must have what's right before using it:

Composite Damage

• Non repaireable component damage with the must replaced as needs too. Area condensation that structure might indicate by that has water and they must be checked. Cosmetic is has outside skin but done structure fibre. Impact it done be object striking its the what might occurred

Delamination, Visual, UT

• It the outer in skin by what's has happening to its the a lot by lightning strikes and moisture, Separating each in ply. This be from poor loading and can seen by not using methods.
• And test, it to must to first check with detect the defrct. The inspection determines what the should be also damage is can the proper process for it.

Inspections and Repairs

• It the for used one to to many things, if used the should be it. Tap can to see what wrong with the. Ultrasound: check internal damage, using the pulse, test emits through the and returns for image is it the requirements for its also

Radiographic and Thermal Diagnostics

X-ray inspection see the see the densities compare around area. Thermography be identifying temperature with is damaged. It gives heat the with IR Sealents been aircraft and are can available it