Jeppesen 07A - Aircraft Structural Metals

Strength.

One way to classify metals is according to the amount of strength they possess. It is determined by the percentage of parent metal and other elements used to make an alloy.

Tension.

When a piece of sheet metal is pulled from each end, the resultant force is called:

Tensile strength.

It is the ability to withstand tension.

Yield strength.

It is the ability of a metal to resist deformation.

Yield point.

When a tensile load is applied to a material, the material resists any deformation until this point is reached. Passing through this point, the metal stretches without an increase in the applied stress.

Ultimate load.

At what load is that when it is reached, the material breaks?

Shear strength.

It describes a metal's ability to resist opposing forces.

Bearing strength.

It is the ability of a joint to withstand any form of crushing or excessive compressive distortion.

Compression load.

Material under this load usually fails by buckling or bending.

Hardness.

It refers to a metal’s ability to resist cutting, penetration, or abrasion. Opposite of malleability.

Malleability.

It is a material's ability to be bent, formed, or shaped without cracking or breaking. Opposite of hardness.

Ductility.

It is the ability of metal to be drawn into wire stock, extrusions, or rods.

Brittleness.

It describes a material's tendency to break or shatter when exposed to stress, and is the opposite of ductility and malleability.

Conductivity.

It is the property which enables a metal to carry heat or electricity.

Thermally conductive.

If a metal is able to transmit heat it is said to be:

Heat exchange.

Before a metal can carry heat away from its source, it must first absorb it. This ability to conduct heat away is called:

Metals that can carry heat also carry electrons, making them good electrical conductors.

Which statement is true about a metal's conductivity?

Electrical conductivity.

It is the measure of a material's ability to allow electron flow.

Gold.

This metal is the best electrical conductor.

Thermal expansion.

It is the property of a metal to expand when heated and shrink when cooled.

Coefficient of expansion.

The amount of expansion or contraction is predictable at specific temperatures and is called its:

Elasticity.

It describes a metal's tendency to return to its original shape after normal stretching and bending.

Elastic limit.

It is the point beyond which the metal does not return to its original shape after a deforming force is removed.

Toughness.

It is a material's ability to resist tearing or breaking when it is bent or stretched.

Fusibility.

It is defined as the ability of metal to be joined by heating and melting.

Fusion joining or welding.

To fuse metal means to melt two or more compatible pieces of metal into one continuous part. What is the correct term used for this?

Density.

It is a material's mass per unit volume.

Wrought.

Those objects that are formed by physically working the metal into shape.

Cast.

These items are formed by pouring molten metal into molds.

Hot-working.

It is the process of forming metal at an elevated temperature when it is in its annealed, or soft condition.

Rolling.

It is a hot-working process that consists of forming hot metal ingots with rollers to form sheets, bars, and beams

Forging.

It is a hot-working process wherein a piece of metal is worked at temperatures above its critical range. It is typically used to form intricate shapes and is accomplished through either pressing or hammering.

Pressing.

This forging process is used to form large and heavy parts. Since a press is slow acting, its force is uniformly transmitted to the center of the material being pressed.

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.

Hammering.

It is 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. Usually referred to as smith forging.

The operator has control over both the amount of pressure applied and the finishing temperature.

What is the greatest advantage of hammering?

Cold-working.

This process is performed well below a metal's critical temperature and ranges from the manual bending of sheet metal for skin repairs to drawing seamless tubing and wire.

Cold-working strain hardens the worked metal, increasing its strength and hardness but decreasing ductility.

Which statement is true about cold-working a metal?

Cold worked material must be heat treated before use.

What statement describes a practice done to a worked metal that undergoes strain hardening through cold working?

Cold-rolling.

This cold-working process refers to the rolling of metal at room temperature to its approximate size.

Cold-drawing.

This cold-working process is used in making seamless tubing, wire, streamlined tie rods, and other forms of stock.

The tubing is cold-drawn through a ring-shaped die with a mandrel or metal bar inside the tubing to support it while it is drawn.

Which statement best describes the procedure in making seamless aircraft tubing?

Extrusion.

It is the process of forcing metal through a die which imparts a required cross-section to the metal.

Flexibility.

What is the principal advantage of the extrusion process?

Pure aluminum.

This metal lacks sufficient strength to be used for aircraft construction. However, its strength increases considerably when it is alloyed, or mixed, with other compatible metals.

By their major alloying ingredient.

How are aluminum alloys classified?

By a four-digit index system.

How are aluminum alloys identified?

The major alloying element used in the formation of the alloy.

What does the first digit of the aluminum alloy four-digit index system identify?

It represents a specific alloy modification. If this digit is zero, it indicates there were no special controls over individual impurities.

What does the second digit of the aluminum alloy four-digit index system identify?

The hundredths of 1 percent above the original 99 percent pure aluminum.

What do the third and fourth digits of the 1xxx series of aluminum alloy identify?

The different alloys in the group.

What do the third and fourth digits of the 2xxx to 8xxx series of aluminum alloy identify?

Pure aluminum.

What aluminum alloy is identified by the four-digit index system as 1xxx?

Copper.

What aluminum alloy is identified by the four-digit index system as 2xxx?

Manganese.

What aluminum alloy is identified by the four-digit index system as 3xxx?

Silicon.

What aluminum alloy is identified by the four-digit index system as 4xxx?

Magnesium.

What aluminum alloy is identified by the four-digit index system as 5xxx?

Magnesium and Silicon.

What aluminum alloy is identified by the four-digit index system as 6xxx?

Zinc.

What aluminum alloy is identified by the four-digit index system as 7xxx?

Other elements.

What aluminum alloy is identified by the four-digit index system as 8xxx?

1xxx series of aluminum alloys.

This series of aluminum alloys represents commercially pure aluminum, of 99 percent or higher purity.

It offers high corrosion resistance, excellent thermal and electrical properties, and is easily worked. However, it is very low in strength.

Which statement best describes the properties of pure aluminum?

2xxx series of aluminum alloys.

This series of aluminum alloys utilize copper as the principle alloying agent.

Susceptibility to inter-granular corrosion when improperly heat-treated.

What is the major drawback of using aluminum-copper alloys?

Aluminum-copper alloy.

This aluminum alloy is mostly used in aircraft structures.

2017 and 2024.

These are two of the mostly used aluminum-copper alloy in the construction of skins and rivets.

3xxx series of aluminum alloys.

This series of aluminum alloys have manganese as the principle alloying element, and are generally considered non-heat treatable.

3003.

This is the most common variation of aluminum-manganese alloys which offers moderate strength and has good working characteristics.

4xxx series of aluminum alloys.

This series of aluminum alloys is alloyed with silicon, which lowers a metal's melting temperature. This results in an alloy that works well for welding and brazing.

5xxx series of aluminum alloys.

This series of aluminum alloys uses magnesium as the principle alloying agent.

Aluminum-magnesium alloys.

These alloys possess good welding and corrosion-resistance characteristics. However, if the metal is exposed to high temperatures or excessive cold working, its susceptibility to corrosion increases.

6xxx series of aluminum alloys.

In this series of aluminum alloys, silicon and magnesium are added and form magnesium silicide which makes the alloy heat-treatable. Furthermore, this series has medium strength with good forming and corrosion-resistance properties.

7xxx series of aluminum alloys.

This series of aluminum alloys are made harder and stronger by the addition of zinc.

7075.

This aluminum-zinc alloy has a tensile strength of 77 KSI and a bearing strength of 139 KSI. However, the alloy is very hard and is difficult to bend.

7178.

This aluminum-zinc alloy is much stronger than the 7075 and has a tensile strength of 84 KSI and a bearing strength of 151 KSI.

Alclad.

It is a pure aluminum coating that is rolled on to the surface of heat-treated aluminum alloy.

The thickness of this coating is approximately 5 percent of the alloy's thickness on each side.

Which statement is true regarding the thickness of Alclad coatings?

If it is penetrated, corrosive agents can attack the alloy within.

What is the major drawback of Alclad coating?

Heat treatment.

It is a series of operations involving the heating and cooling of metals in their solid state. Its purpose is to make the metal more useful, serviceable, and safe for a definite purpose.

One is called solution heat treatment, and the other is known as precipitation heat treatment.

Which one of the following statements best describes the types of heat treatment used on aluminum alloys?

It is the process of heating certain aluminum alloys to allow the alloying element to mix with the base metal.

Which one of the following statements defines solution heat treating?

Metal is heated in either a molten sodium or potassium nitrate bath or in a hot-air furnace to a temperature just below its melting point. The temperature is then held and the base metal is soaked until the alloying element is uniform throughout. Then, it is removed from the furnace and cooled or quenched.

Which one of the following statements best describes the process of solution heat treating?

Excessive precipitation increases the likelihood of intergranular corrosion.

It is extremely important that no more than about ten seconds elapse between removal of an alloy from the furnace and the quench. What is the most likely reason for this?

A quenching medium is selected to ensure the proper cooling rate.

What practice is usually done to help minimize the amount of alloying element that precipitates out of a base metal for aluminum alloys?

An alloy is allowed to cool at room temperature.

What is natural aging?

The aging process can be accelerated by reheating a metal and allowing it to soak for a specified period of time.

How can an aluminum alloy's aging process be lengthened?

The aging process can be slowed by storing a metal at a sub-freezing temperature immediately after it is removed from the quench.

How can an aluminum alloy's aging process be shortened?

This process accelerates the aging process and develops hardness, strength, and corrosion resistance by locking a metal's grain structure together.

What is artificial age-hardening?

This process accelerates the aging process and develops hardness, strength, and corrosion resistance by locking a metal's grain structure together.

What is precipitation-hardening?

This process accelerates the aging process and develops hardness, strength, and corrosion resistance by locking a metal's grain structure together.

What is precipitation heat treatment?

Annealing.

It is a process that softens a metal and decreases internal stress. It is the opposite of hardening.

The metal's temperature is raised to an annealing temperature and held there until the metal becomes thoroughly heat soaked. It is then cooled to 500°F at a rate of about 50°F per hour.

What is the process of annealing an aluminum alloy?

If clad aluminum is exposed to excessive heat, some of the core material tends to mix with the cladding.

When annealing clad aluminum metals, they should be heated as quickly and as carefully as possible. What is the reason for this?

Commercially pure aluminum does not benefit from heat treatment since there are no alloying materials in its structure.

Which statement is true regarding the heat treatment of commercially pure aluminum?

5052.

This alloy is the most important of the nonheat-treatable aluminum alloys. It contains about 2.5 percent magnesium and a small amount of chromium. It is used for welded parts such as gaso­line or oil tanks, and for rigid fluid lines. Its strength is increased by cold working.

Solution heat treated.

What does the heat treatment identification "-T" mean?

Annealed (cast products only).

What does the heat treatment identification "-T2" mean?

Solution heat-treated, followed by strain hardening.

What does the heat treatment identification "-T3" mean?

The material has been solution heat-treated and has had its thickness reduced 6 percent by cold rolling.

What does the heat treatment identification "-T36" mean?

Solution heat-treated, followed by natural aging at room temperature to a stable condition.

What does the heat treatment identification "-T4" mean?

Artificially aged after being rapidly cooled during a fabrication process such as extrusion or casting.

What does the heat treatment identification "-T5" mean?