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