Aerospace metals in the Airbus A380-800

The Airbus A380-800 has a max. take-off weight of approximately 530 tons, of which about 140 tons consists of Aluminium alloy structure, about 35 tons of carbon fibre reinforced plastics, titanium structure and high strength steel parts account for roughly 15 tons and 13 tons respectivly.

This excludes the 4 engines of 80 000 lbs of thrust each which are not accounted for in this picture.

Assessing the material distribution as a percentage of the total structure weight and comparing with the Airbus A340, one can immediately draw the following conclusion:

• Aluminium will still be the most widely used material in airframe design with a 68 % share;
• there is a growing interest in Titanium alloys resulting in a reduced utilization of high strength steel;
• the use of CFRP carbon fibre reinforced plastic for the manufacture of large transport aircraft has apparently stabilized.
• the balance is a small fraction of miscellaneous materials.

Aerospace aluminium.

Aluminium alloys remain a key airframe material, particularly for civil aircraft. Fatigue optimization is the challenge for the next generation of aircraft, with improved understanding and controlling of physical processes using improved analysis and design tools.

Aerospace aluminium rolled products.

Aerospace uses aluminium rolled products, cast materials and aluminium extruded sections. The aluminium comes from smelter plants.

Aluminium mills cold roll aluminium sheet products up to 2800mm wide, which are supplied annealed and processed for aerospace and automotive use.

Aircraft plate and sheet.

The aerospace industry is constantly driving to reduce weight in an on going bid to reduce fuel consumption and, by extension, operating costs. More recently, pressure for air travel to be more ‘green’ has also come into the equation. Much work has been done to reduce airframe weight and today’s civil aircraft are full of composite materials and lightweight alloys. This includes development work to replace the traditional steels and nickel-base alloys used in engines. Aluminide base alloys offer superior high temperature performance with low weight and non-burn.

Aluminium alloys.

Advanced Al-alloys have improved properties in strength and fracture toughness and can generate a weight reduction of approx. 5 to 8%.
Al-alloys of the 6xxx series, such as 6013 from ALCOA and the 6057 from Pechiney are under investigation for their effectiveness for welded applications.
Al-Lithium alloys still take an important part in the Airbus R&D program for its outstanding weight saving potential mainly due to its lower density.
Beside the remaining traditional western supplier ALCAN a further chance is seen in the cooperation with Russian aerospace stockholders and advanced materials suppliers. Al-Li alloys have been widely used in Russia for applications on fighter airplanes. Conversion of material standards to transport aircraft requirements is in hand.
GLARE, a newly developed Fibre Metal Laminate is another strong candidate to be used in the design of fuselage structures.
Between 15 and 28% of weight reduction over today's design practice could be achieved in typical areas of fuselage structures.

Aerospace titanium.

Titanium will progressively replace high strength steel mainly in engine pylon and landing gear structures.
Advanced alloys with improved strength and damage tolerance properties show a weight reduction potential up to 15% in such areas.

Aerospace stainless steel.

An alloy of iron, chromium, and nickel that is resistant to rust and corrosion. Stainless steel is more correctly called corrosion-resistant steel. Neither 200 series stainless steel nor 300 series stainless steel can be hardened by heat treatment, and the steel in both of these series is non-magnetic. The 400 series of stainless steel which can be hardened by heat treatment and is magnetic is used for knife blades and razor blades.
The low carbon version of 300 series stainless steel or Austenitic Stainless Steel, as it is sometimes known, is used to avoid corrosion problems caused by welding.
This type of stainless steel hardens at a relatively lower temperature. In the initial stage, it is austenitic. Sometimes other elements are added to it in order to make it tougher. Among all the types of stainless steels, precipitation hardened stainless steel can be transformed into different shapes by heating. It is as corrosion resistant as austenitic stainless steel. It is prominently used in making aircraft components.

Steel.

The use of steel with its high specific gravity prevented its widespread use in aircraft construction, but it has retained some value as a material for aerospace castings, ie for small components demanding high tensile strengths, high stiffness and high resistance to wear. Such components include undercarriage pivot brackets, wing-root attachments, fasteners and tracks.

Although the attainment of high and ultra-high tensile strengths presents no difficulty with steel, it is found that other properties are sacrificed and that it is difficult to manufacture into finished components. To overcome some of these difficulties types of steel known as maraging steels were developed in 1961, from which carbon is either eliminated entirely or present only in very small amounts. Carbon, while producing the necessary hardening of conventional high tensile steels, causes brittleness and distortion; the latter is not easily rectifiable as machining is difficult and cold forming impracticable. Welded fabrication is also almost impossible or very expensive.

The hardening of maraging steels is achieved by the addition of other elements such as nickel, cobalt and molybdenum. A typical maraging steel would have these elements present in the proportions: nickel 17-19 per cent, cobalt 8-9 per cent, molybdenum 3-3.5 per cent, with titanium 0.15-0.25 per cent. The carbon content would be a maximum of 0.03 per cent, with traces of manganese, silicon, sulphur, phosphorus, aluminium, boron, calcium and zirconium. Its 0.2 per cent proof stress would be nominally 1400 N/mmz and its modulus of elasticity 180 000 N/mM2.

The main advantages of maraging steels over conventional low alloy steels are: higher fracture toughness and notched strength, simpler heat treatment, much lower volume change and distortion during hardening, very much simpler to weld, easier to machine and better resistance to stress corrosion/hydrogen embrittlement.
Maraging steels are traditionally used for structural forgings.