Materials and Process

Metal Working

Process of changing raw metal into useful aircraft components.

Metal Working Categories

Forming, Cutting, and Joining.

Forming

Changes the shape of metal without removing material.

Hot Working

Forming metal at an elevated temperature when it is in its soft condition (annealed state).

Wrought

Metal that has been mechanically worked rather than cast.

Hot Working Temperature

Above the metal's critical or recrystallization temperature.

Hot Working Advantages

Easier forming, reduced internal stresses, refined grain structure, and greater ductility.

Hot Working Disadvantages

Oxidation, poorer surface finish, lower dimensional accuracy, and requires heating equipment.

Rolling

Forming hot metal ingots with rollers to form sheets, bars, and beams.

Rolling Products

Sheets, bars, beams, and structural stock.

Forging

Worked at temperatures above the critical range through pressing or hammering.

Forging Methods

Pressing, drop forging, and hammering.

Forging Advantage

Produces superior grain flow, strength, toughness, and fatigue resistance.

Forging Applications

Landing gear, connecting rods, crankshafts, structural fittings, and bolts.

Casting

Formed by pouring molten metal into molds.

Casting Advantages

Produces complex shapes with minimal machining.

Casting Disadvantages

Lower strength than wrought products and may contain porosity or shrinkage defects.

Casting Applications

Engine housings, gearbox cases, pump housings, and brackets.

Cold Working

Working metal below its critical temperature.

Cold Working Other Names

Strain hardening or work hardening.

Cold Working Examples

Manual bending, cold rolling, and cold drawing.

Cold Working Effect

Increases hardness, strength, and yield strength while decreasing ductility and malleability.

Cold Working Cause

Plastic deformation creates dislocations that make further deformation more difficult.

Extrusion

Forcing metal through a die which imparts a required cross-section to metal.

Extrusion Temperature

Can be performed either hot or cold.

Extrusion Applications

Stringers, longerons, seat tracks, channels, and window frames.

Cutting

Removes unwanted material to obtain the desired dimensions.

Joining

Combines two or more parts into one assembly.

Joining Methods

Riveting, welding, brazing, soldering, adhesive bonding, and bolting.

Hot Working vs Cold Working

Hot working shapes heated soft metal; cold working shapes metal below the critical temperature and strain hardens it.

Casting vs Forging

Casting uses molten metal in molds; forging shapes heated solid metal by pressure.

Extrusion Memory Aid

Metal exits a die with the same cross-sectional shape.

Forging Memory Aid

Forging = Force.

Casting Memory Aid

Casting = Container (mold).

Hot Working Memory Aid

HOT = SOFT.

Heat Treatment

Involves heating and cooling of metals in their solid state.

Heat Treatment Purpose

Makes metal more useful, serviceable, and safe for a definite purpose.

Heat Treatment State

Performed while the metal remains in the solid state.

Hardening

Produces a harder, stronger, and more impact-resistant metal.

Annealing

Produces a softer, more ductile metal with reduced internal stress.

Heat Treatment Variables

Heating temperature and rate of cooling.

Soft Phase

Heating stage that prepares the metal for strengthening.

Hard Phase

Cooling stage that develops the desired hardness and strength.

Heat Treatment vs Metal Working

Heat treatment changes properties; metal working changes shape.

Heat-Treatable Aluminum Alloys

Gain strength through solution heat treatment, quenching, and aging.

Non-Heat-Treatable Aluminum Alloys

Cannot be strengthened by heat treatment and rely on strain hardening.

Non-Heat-Treatable Alloys

Commercially pure aluminum, manganese alloys, and magnesium alloy 5052.

Only Heat Treatment for Non-Heat-Treatable Alloys

Annealing.

Solution Heat Treatment

Thermal process used to enhance the properties of alloyed metals.

Solution Heat Treatment Purpose

Heating certain aluminum alloys to allow the alloying element to mix with the base metal.

Solution Heat Treatment Temperature

Heated just below the melting point (870–940°F or below 1220°F).

Soaking

Holding the alloy at temperature until the alloying elements become uniformly distributed.

Soaking Time

10 minutes to 2 hours, nominally 1 hour per inch of cross-section.

Quenching

Rapid cooling after solution heat treatment.

Quenching Requirement

Must occur within 10 seconds to prevent premature precipitation.

Quenching Media

Water spray, water bath, or hot water.

Natural Aging

Cooling at room temperature until the alloy reaches a stable condition.

Natural Aging Time

Hours to weeks.

Copper Alloy Aging

Gains about 90% strength in 30 minutes and becomes fully hard in 4–5 days.

Artificial Aging

Accelerates aging by reheating the alloy.

Artificial Aging Other Names

Artificial age hardening, precipitation hardening, or precipitation heat treatment.

Artificial Aging Temperature

250–375°F.

Artificial Aging Soak Time

6–10 hours or up to 24–28 hours.

Artificial Aging Purpose

Develops hardness, strength, and corrosion resistance by locking the grain structure together.

High Zinc Alloys

Require artificial aging to develop full strength.

Aluminum Heat Treatment Sequence

Solution heat treatment → Soaking → Quenching → Natural aging or Artificial aging.

Aluminum Annealing

Softens a metal and decreases internal stress.

Annealing Opposite

Hardening.

Annealing Temperature

650–775°F.

Full Annealing

750–800°F with approximately 2–3 hours soak time, cooled to 500°F at 50°F per hour.

Partial Annealing

640–670°F with up to 2 hours soak time, cooled to 450°F at 50°F per hour.

Stabilizing Anneal

350°F for less than 1 hour, cooled in still air.

Reheat Treatment

Heat-treated material can be reheat treated any number of times.

2017 and 2024 Aluminum

Often reheated to soften them enough for driving rivets or forming.

Clad Material Reheat Limit

Generally limited to no more than three reheat treatments.

Reason for Clad Reheat Limit

Diffusion of core material into the cladding decreases corrosion resistance.

Strain Hardening

Cold working below the metal's critical temperature.

Strain Hardening Applications

Used on both heat-treatable and non-heat-treatable aluminum alloys.

H2 Temper

Strain hardened and partially annealed.

T Temper

Heat treatment designation for heat-treatable aluminum alloys.

T2

Annealed (cast only).

T3

Solution heat-treated and strain hardened.

T4

Solution heat-treated and naturally aged.

T5

Artificially aged after rapid cooling during fabrication.

T6

Solution heat-treated and artificially aged (precipitation heat-treated).

T7

Solution heat-treated and stabilized.

T8

Solution heat-treated, strain hardened, and artificially aged.

T9

Solution heat-treated, artificially aged, and strain hardened.

T10

Artificially aged and cold worked.

F Temper

As fabricated (wrought) or as cast.

O Temper

Annealed and recrystallized (wrought only).

H Temper

Strain hardened.

H1

Strain hardened only.

H2

Strain hardened and partially annealed.

H3

Strain hardened and stabilized.

H4

Strain hardened and baked.

Hx2

Quarter hard (2/8).

Hx4

Half hard (4/8).

Hx6

Three-quarter hard (6/8).

Hx8

Full hard (8/8).