Aerospace Materials

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Metal Alloys for Aerospace Application
An alloy is a mixture or solid solution of two or more metals. The atoms of one replace the atoms of the other or occupy interstitial positions between the atoms. • • • • • • Aluminum alloys Titanium alloys Steels Magnesium alloys Nickel alloys Beryllium alloys
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Aluminum Alloy Characteristics
• Aluminum alloys are the most widely used materials in aircraft structures. • Al alloys are easily formed and machined. • Al alloys are relatively inexpensive. • Al alloys experience a significant reduction in strength at higher temperatures, limiting their application in supersonic aircraft.
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Aluminum Alloys
Aluminum alloys are identified by a four-digit numbering system that signifies the primary alloying element. • • • • • • • 1000 2000 3000 4000 5000 6000 7000 99% elemental Al Copper Manganese Silicon Magnesium Magnesium and Silicon Zinc
Shear:
σsu = Ultimate Stress G = Modulus of Rigidity
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Material Forms for Metals
• Sheet and plate – a rolled, flat product
– Sheet thickness less than 0.250 in. – Plate thickness 0.250 in. or greater
• Extrusion – uniform cross section created by forcing metal through a series of dies • Forging – shape created by plastically deforming metal by compression, usually in closed dies. Forging creates high-strength, tough part with efficient use of material. • Casting – created by solidification of liquid material in a mold
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Applications for Material Forms
• Sheet and plate
– Sheets are used in skin of fuselage, wings, control surfaces, etc. – Plates are machined to varying thickness create optimum shapes in high-cost parts
Aerospace Materials
• Selection of materials for a given application • Aerospace metal alloys – Properties – Relative costs • Composite materials – Material properties – Analysis methods – Manufacturing
• Group 7000: Compression applications or where static strength is more important than fatigue or damage tolerance
– – – – Upper wing surfaces Wing ribs Floor beams 7075-T6, especially in military jets
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Steel Alloys
Steel alloys are identified by a four-digit numbering system. The first two digits identify the primary alloying elements, while the last two signify the carbon content. • 4130 • 4340 Cr-Mo with 0.3% C Ni-Cr-Mo with 0.4% C
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Aluminum Alloys for Airframe Structures
• Group 2000: Primarily in tension applications where fatigue and damage-tolerant design are critical
– Lower wing skins – Pressurized fuselage skins – Standard material has been 2024-T3
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Titanium Alloys
• Titanium alloys offer, with their higher strength, offer higher structural efficiencies than Al alloys. • Ti alloys are offer selected due to high temperature endurance. • Ti alloys are significantly more expensive than Al (high material cost, more difficult to form and machine). • Galvanic corrosion resistance for fastening composite structures. • The most common alloy is Ti-6Al-4V.
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Material Selection
The first factor to be considered in selection of a material for a given component is the application. • Operational features – principal function of the component; description of principal loads and environment • Design Criteria – most important design properties for satisfying the operational features • Manufacturing Processes – Material form and fabrication processes.
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Mechanical Properties
Most common metallic materials used for aerospace design are Aluminum, Steel, and Titanium. The properties for these materials are contained in MIL-HDBK-5. Typical data includes:
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Steel Alloys
• Steel contains iron with a small percentage of carbon (0.02 to 1.7%). Other alloying elements are added to achieve specific properties such as strength, toughness, or corrosion resistance. • The mechanical properties of steels can be varied significantly by heat treating. • Some steels offer very high strength. • Steel alloys are not widely used in airframe structures except where very high strength is needed.
Processing used to produce specific properties (such as heat treatment) are designated by a dashed suffix following the four-digit alloy, e.g., 2024-T3.
• Extrusion – used for uniform cross section parts (e.g., stiffeners on spars, ribs) where higher strength is needed • Forging – nonuniform cross section parts where highstrength is needed. • Casting – lower cost parts in noncritical areas