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Aircraft Materials
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AIRCRAFT MATERIALS AND PROCESSES
HOLY ANGEL UNIVERSITY – ENGR. AMORSOLO T. CHUA
Properties of Materials
Properties of Material
• Hardness
- refers to the ability of a material to resist abrasion, penetration, cutting action, or permanent distortion.
• Strength
- one of the most important properties of a material is strength. Strength is the ability of a material to resist deformation. Strength is also the ability of a material to resist stress without breaking.
• Density
- Is the material’s mass per unit volume.
• Malleability
- is the ability to be bent or molded into different forms.
• Ductility
- Is the ability to be drawn out into a thin wire form.
• Elasticity
- is the property that enables a metal to return to its original size and shape when the force which causes the change of shape is removed.
• Toughness
-a material which possesses toughness will withstand tearing or shearing and breaking.
• Brittleness
- describes a material's tendency to break or shatter when exposed to stress.
• Fusibility
- is the ability of a metal to become liquid by the application of heat.
• Conductivity
- is the property which enables a metal to carry heat or electricity.
• Thermal Expansion
- refers to contraction and expansion that are reactions produced in metals as the result of heating or cooling.
Classifications of Metal
Non-Ferrous Metal
• Much of the metal used on today's aircraft contains no iron.
• Aluminum, copper, titanium, and magnesium are some of the most common nonferrous metals used in aircraft construction and repair.
Aluminum alloys
* For 1xxx series, the last two digits indicates hundredths above 1 percent of pure aluminum.
List of most generally used alloy types for aircraft structural aluminum:
• Alloy 1100
-Is a low strength, commercially pure aluminum that can be only be used in non-structural applications where strength is not important.
• Alloy 2024
- Is the most popular structural aluminum alloy. Its strength is equivalent to the mild steel, but its susceptible to corrosion.
• Alloy 3003
- It is similar to 1100 and is used for the same types of applications. It is nonheat treatable but it can be hardened by cold working.
• Alloy 5052
- Is used for welded applications such as fuel tanks and for rigid fluid lines.
• Alloy 6061
- Used in applications where heat treatability, ease forming, medium strength, and good corrosion resistance are needed.
• Alloy 7075
- Used for high strength structural requirements.
Clad Aluminum
- An aluminum alloy sheet that has a coating of pure aluminum rolled onto its surface.
- The pure aluminum cladding protects the core alloy sheet from corrosion.
Other alloys
• Magnesium and Magnesium Alloy
- Is the lightest structural metal, weighing only about two thirds as much as aluminum.
• Copper and Copper Alloy
- high electrical and heat conductivity.
• Titanium and Titanium Alloy
- Has high structural strength which it retains to high temperature. It is used in turbine engines, and for aircraft skins in areas where the temperature is high.
Titanium Designation
1. A (alpha) - all around performance, good weldability
2. B (beta) – bendable, excellent bend ductility
3. C ( alpha beta) – combination of alpha and beta.
Ferrous Metal
• Any alloy containing iron as its chief constituent is called a ferrous metal.
• The most common ferrous metal in aircraft structures is steel.
SAE Classification of Steels
SAE Four-digit System
First Digit: basic alloying element
Second Digit: the percentage of the basic element in the alloy
Third and Fourth: percentage of carbon in the alloy in hundredths of a percent
1xxx – Carbon Steel
• The greater the carbon content, the more receptive steel is to heat treatment and, therefore, the higher its tensile strength and hardness.
• Types of Carbon Steel:
1. Low-carbon Steel – containing 0.10% and 0.30% carbon.
2. Medium-carbon Steel – containing 0.30% and 0.50% carbon.
3. High-carbon Steel – containing 0.50% and 1.05% carbon.
2xxx – Nickel Steel
• Adds strength and hardness to steel
• SAE 2330 steel is used for aircraft bolts, cable terminals, keys, clevises, and pins.
3xxx – Nickel chromium Steel
• Nickel gives toughness to steel, and chromium hardens it.
• SAE 3130 and 3250 are used for forged and machined parts
4xxx – Chrome-molybdenum Steel
• This alloy combines toughness and high strength with ease of welding and machining.
• SAE 4130 is used extensively for welded steel structure such as fuselage frames, landing gear, and engine mounts.
5xxx – Chromium Steel
• Increase the hardness of steel.
6xxx – Chrome-vanadium Steel
• Used extensively for wrenches and other hand tools where extremely high strength and hardness are essential.
Metal Working Processes
• Wrought objects - are those formed by physically working the metal into shape.
• Cast items - are formed by pouring molten metal into molds.
Three methods commonly used
• Hot working
• Cold working
• Extruding
Hot Working
• Forging - is typically used to form intricate shapes and is accomplished through either pressing or hammering.
1. Pressing - It is used to form large and heavy parts. This affects the interior grain structure resulting in the best possible structurethroughout.
2. Drop Forging - It is a hammering process whereby a hot ingot is placed between a pair of formed dies in a machine called a drop hammer and a weight of several tons is dropped on the upper die.
3. Hammering/Smith forging - A type of forging that is usually used on small parts because it requires a metalworker to physically hammer a piece of metal into its finished shape.
Cold Working
• Cold-working strain hardens the worked metal, increasing its strength and hardness but decreasing ductility.
1. Cold Rolling - Usually refers to the rolling of metal at room temperature to its approximate size.
2. Cold Drawing - It is used in making seamless tubing, wire, streamlined tie rods, and other forms of stock.
Extrusion
• The process of forcing metal through a die which imparts a required cross-section to the metal.
Heat Treatment
Heat Treatment
• A process of heating a metal to improves the metal properties such as hardness, ductility, toughness and others.
• It may also remove some internal and external stresses and strain to reduce metal failure.
Critical Temperature of a Metal - the temperature at which the internal structure of a metal takes on a crystalline form.
Ferrous Metal Heat Treatment
1.)Hardening
- The metal is heated at the furnace with a temperature above its critical temperature, quench it at this temperature, and allow cooling at room temperature.
Quenching Medium:
1. Brine – fastest quench that produces the hardest steel.
2. Water – produces slightly less hardness.
3. Oil – slowest quench.
2.) Normalizing
- The metal is heated to a temperature above its critical temperature and allowed to cool in still air.
3.) Annealing
- Also called softening.
- Annealing produces a fine-grain, soft, ductile metal without internal stresses or strains.
- By heating the steel metal to just above the upper critical point.
4.) Tempering
- A form of heat treatment in which brittleness is removed from the metal but it may also reduces some hardness.
5.) Case Hardening
a.) Nitriding- A method of case hardening steel by heating it in an atmosphere of ammonia.
b.) Carburizing - A case hardening process in which additional carbon is infused into the surface of low- carbon steel.
Non-ferrous Metal Heat Treatment
1.Solution Heat Treatment
- Also called natural aging
- For maximum strength the metal must be quenched immediately after it is taken from the oven so it will have the smallest grain size possible.
Intergranular Corrosion – corrosion that forms along the grain boundaries in a piece of metal.
2.) Precipitation Heat Treatment
- Also called artificial aging
- Artificial aging greatly increases the strength and hardness of the metal, but it decreases the ductility; the metal becomes more difficult to bend and form.
3.) Annealing
- A form of heat treatment in which a metal is made soft.
Temper Designations • Basic Temper Designation
• F – As fabricated
• O – Annealed
• H – Strain hardened (Non heat treatable products only)
• Temper Designation for Non Heat Treatable Alloys
• H1 – Strain hardened produced by cold working the metal to the desired dimension.
• H2 – Strain hardened, then partially annealed to remove some of the hardness.
• H3 – Strain hardened, then stabilized.
• The degree of hardening is indicated by a second digit following one of the above designations:
• 2 - 1/4 hard
• 4 - 1/2 hard
• 6 - 3/4 hard
• 8 - full hard
• 9 - extra hard
Temper Designation for Heat Treatable Alloy
• T1 – Solution Heat Treated
• T2 – Annealed
• T3 – Solution heat treated and cold worked.
• T4 – Solution heat treated and naturally aged.
• T5 – Cooled from an elevated temperature shaping process and artificially aged
• T6 – Solution heat treated and artificially aged.
• T7 – Solution heat treated and stabilized
• T8 – Solution heat treated, cold worked, and artificially aged
• T9 – Solution heat treated, artificially aged, and cold worked
• T10 – Artificially aged then cold worked
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