Aluminium and Aluminium Alloys (Wrought and Casting Alloys): Light Weight Engineering Materials for Industrial Applications

By Dr Thoguluva Raghavan Vijayaram PhD

Senior Lecturer Department of Manufacturing Process and System Faculty of Manufacturing Engineering, UTeM Universiti Teknikal Malaysia Melaka Ayer Keroh, 75450 Melaka Malaysia Email: vijayaram1@gmail.com

Aluminium is the most abundant metallic element, representing about 8% of the earth’s crust. The primary source of aluminium is bauxite, which is processed into hydrated aluminium oxide by the Bayer process. From aluminium oxide, 99.5% to 99.9% pure aluminium is extracted by the Hall process, which uses electrolytic cells where the oxide is reduced to pure aluminium. It is light in weight, yet some of its alloys have strengths greater than that of structural steel. It ranks second in the metals market after iron and steel. The rapid growth of the aluminium industry is attributed to a unique combination of properties which makes it one of the most versatile of engineering and construction materials. It has good thermal and electrical properties and high reflectivity to both heat and light. It is highly corrosion-resistant under many service conditions. Besides, it is soft, ductile and possesses lower specific gravity. It can be cast and worked into almost any form and can be given a wide variety of surface finishes. The structure of pure aluminium is characterized by a relatively pure aluminium matrix. With all these outstanding properties, it has come to be of prime importance as engineering materials for various industrial applications. Aluminium has excellent castability, weldability, and machinability. The technology has been advanced such that aluminium base ball bats are now made from high strength aluminium tubing and possess desirable weight distribution, center of percussion, sound and impact dynamics. Aluminium and its alloys are nonmagnetic.

Aluminium is consumed by building and construction, transportation, electrical, machinery and equipment, containers and packaging industries. Commercial purity aluminium varies from about 99.3% Aluminium minimum to 99.7%. It responds well to decorative finishes and shows excellent corrosion resistance. The high purity aluminium is selected for applications such as electrical conductor alloys and reflector sheet. The good thermal conductivity of aluminium has led to its application as radiator fin material in baseboard heating and air-conditioning units. Excellent light reflectivity and corrosion resistance account for its use as a sheet metal light reflector and a coating for high-grade optical reflectors. Its softness and ductility, coupled with its corrosion resistance and nontoxic nature, have resulted in its use as a foil and packaging material. Transportation industry is one of the largest consumers of aluminium.

The principal uses of aluminium and its alloys, in decreasing order of consumption, are in containers and packaging as aluminium cans, and foils, in buildings and other types of construction, in transportation industries like aircraft and aerospace, bus, automobile, rail road car, pipe lines, and marine craft. In the electrical application industries, aluminium is used to process nonmagnetic electrical conductor. Consumer durables like appliances, cooking utensils, and furnitures are made from aluminium.

Nearly, all high voltage transmission wiring is made of aluminium. Aluminium and its alloys are applied in sheet metal work, spun hollow ware, and tin stock. Truck wheels, screw machine products, and aircraft structures are made from it. Chemical equipments, pressure vessels, builder’s hardware, and storage tanks are manufactured and fabricated from aluminium. Porous aluminium has been produced recently that are 37% lighter than solid aluminium and have uniform permeability and microporosity. This characteristic allows their use in applications where a vacuum or differential pressure has to be maintained. Examples are the vacuum holding of fixtures for assembly and automation and the vacuum forming or thermoforming of plastics. For nonelectrical applications, aluminium is used in the form of alloys. These have greater strength than pure aluminium, yet retain the advantages of light weight, good conductivity, and corrosion resistance. On strength to weight basis, most of the aluminium alloys are superior to steel and other structural metals.

Aluminium generally replaces steel or cast iron where there is a strong need for light weight, corrosion resistance, low maintenance expense, or high thermal or electrical conductivity. In modern motor vehicles, aluminium is used to manufacture automobile parts such as body panels, engine blocks, manifolds, and transmission cases, where the reduced weight serves to increase fuel economy. Duralumin is the oldest age hardenable aluminium alloy. The attractive feature of this alloy is the fact that ductility does not significantly decrease during the strengthening heat treatment. In general, the high ductility and low yield strength of aluminium alloys make them appropriate for almost all operations. Good dimensional tolerances and fairly intricate shapes can be produced easily.

Aluminium alloys are classified into two major groups as wrought alloys, and casting alloys, based on the fabrication method. Wrought alloys are those that are shaped as solid engineering components by plastic deformation, and are therefore designed to have attractive forming characteristics, such as low yield strength, high ductility, good fracture resistance, and excellent strain hardening. Wrought aluminium is often produced as Alclad material. A thin layer of corrosion resistant aluminium is bonded to one or both surfaces of the high strength alloy during rolling and the material is further processed as a composite. Remarkable features for the casting alloys include low melting point, high fluidity, and attractive as cast solidified structures and superior properties.

Aluminium Lithium alloys with higher strength, greater stiffness, and lighter weight is considered as an emerging and an attractive aerospace material. Each percent of lithium, up to 4 % reduces the overall weight by 3% and increases stiffness by 6%. Alloys have already been developed that have 8 to 10 % lower density, 15% to 20% greater stiffness, strengths comparable to those of existing alloys, and good resistance to fatigue crack propagation, but fracture toughness, ductility, and stress corrosion resistance are usually poorer than for conventional alloys. They are highly machinable, can be welded, and are readily adaptable to forming by forging or extrusion. Some sheet material can be even fabricated by superplastic forming. Thus, significant weight savings can be achieved without the major overhaul of manufacturing equipment that would be associated with a switch to advanced composites. Aluminium Manganese alloys contains 1.2% Manganese produces a moderately strong non heat treatable aluminium alloy. The manganese addition strengthens the aluminium by solid solution strengthening and by a fine dispersion of precipitates. Further, strength is increased by increasing the magnesium addition up to about 1 percent. These alloys are used for general purposes where moderate strength and good workability are required. These alloys are used to manufacture cooking utensils, building products such as siding, and gutters.

Aluminium Magnesium alloys are non heat treatable aluminium alloys. General purpose and structural Aluminium Magnesium alloys contain from 1% to slightly over 5% Mg are in widespread industrial use. These alloys have been developed as finishing and decorative alloys. It has a wide range of strength, good formability, welding characteristics, and a high resistance to corrosion. An outstanding property of such alloys is the good welding response of the higher strength alloys when argon shielded arc welding processes are used. Aluminium Magnesium alloys is used to process utensils, architectural trim, electrical conductors, refrigerator trim, coiled tubes, hydraulic tubes, cable sheathes, rivets, screen wire, zippers, aircraft parts, marine parts, automobile parts, unfired and welded pressure vessels, television towers, drilling rigs, transportation equipments, missile components, armor plates, welded structures, storage tanks, welding rods, wire, and electrodes, and anodized auto and appliance trim.

Aluminium Copper alloy contains 5.5% copper has a much wider and higher range of strength as well as good weldability, superior resistance to stress corrosion, and higher elevated temperature properties. Aluminium Copper alloy with 5.5% Copper, 0.40% Bismuth, and 0.4% Lead is used when good cutting and chip characteristics are necessary for high speed production of screw machine parts. This alloy is the basic aluminium screw machine alloy, and it is used as a reference standard for the machinability of aluminium alloys. These alloys are used to manufacture screw machine products, forgings, aircraft products, high strength weldments for cryogenic and aircraft parts.

Aluminium Copper Magnesium alloys were the first discovered precipitation hardenable alloys. Additions of magnesium to aluminium copper alloys greatly accelerate and intensify precipitation hardening in aluminium copper alloys. These alloys are processed to produce truck frames, aircraft structures, screw machine products, fittings, aircraft engine cylinder heads and pistons, jet engine impellers, compressor rings, and aircraft engines.

Aluminium Magnesium Silicon alloys contains 0.6 to 1.2 percent Magnesium, and 0.4 to 1.3 percent Silicon in aluminium. It forms the basis for the series of wrought precipitation hardenable aluminium magnesium silicon alloys. These alloys are used to clad sheets and plates. Trucks, marine structures, rail road cars, furnitures, automobile body sheets, rivets, heavy duty structures, bridge rails, pipes, architectural extrusions, forged parts for welded structures, high strength bus conductors and busbars, and electrical conductor wires are manufactured from aluminium magnesium silicon alloys. The Aluminium Magnesium Silicon alloys have excellent corrosion resistance in all natural atmospheric environments and in many artificial ones. The corrosion resistance of these alloys is best in materials which are quenched rapidly and aged artificially to the desired temper.

Aluminium alloys are cast in considerable quantity, and the most popular aluminium silicon alloy with an eutectic composition has low melting point, good fluidity, and high as cast strength. Aluminium casting alloys are designed for both properties and process. When the strength requirements are low, as cast properties are usually adequate. High strength aluminium alloy castings usually require the use of alloys that can subsequently be heat treated. The aluminium alloys used for permanent mold casting are designed to have lower coefficients of thermal expansion or contraction, because the molds offer restraint to the dimensional changes that occur upon cooling.

Aluminium casting alloys have been developed for casting qualities such as fluidity, and feeding ability, as well as for properties such as strength, ductility, and corrosion resistance. The major alloying elements for aluminium casting alloys are copper, silicon with copper and or magnesium, silicon, magnesium, zinc, and tin. Aluminium Copper casting alloys are processed to manufacture general purpose sand castings, manifold and valve body castings, washing machine agitator parts, timing gear castings, fuel pump body castings, and structural castings requiring high strength and shock resistance.

Aluminium Silicon Copper casting alloys are used to make as cast ornamental grilles, meter housing castings, automotive engine cylinder castings, aircraft component castings, and missile part castings.

Aluminium Silicon Magnesium casting alloys are widely applied to manufacture automotive pistons, pump bodies, liquid cooled cylinder heads, crank cases, accessory housings, aircraft fixtures, blower housings, snow removal equipments, scaffold pedestals, and wheels for aerospace applications. Besides, these casting alloys are used to produce transmission cases, truck axle housings, cylinder blocks, railway tank car fittings, marine hardware, fan blades, and pneumatic tools. Aluminium Copper Magnesium Nickel casting alloys are used to cast automotive pistons, diesel engine pistons, and pulley sheaves, and engine parts operating at elevated temperatures. In addition to these castings, it is used to manufacture large, intricate castings with thin sections for instrument cases, and typewriter frames.

About the author
Dr.Thoguluva Raghavan Vijayaram, currently working as Senior Lecturer in the Faculty of Manufacturing Engineering at UTeM, Universiti Teknikal Malaysia Melaka, Malaysia. He hails from India and he has completed his PhD Research Degree in Mechanical Engineering (Metal Matrix Composites: Materials Engineering) from the Faculty of engineering, Universiti Putra Malaysia. He has published quality research papers in reputed International journals, National journals, International conference proceedings and in the Malaysian broadsheet. He has a wide range of work experience, both in academics and as well as in industry, consultancy, and teaching and especially in research and development work. His areas of expertise include: Metallurgical Engineering, Mechanical Engineering and Manufacturing Engineering and his special areas of research interests are in the field of advanced casting technology and techniques, composite materials and processing, powder metallurgy, Ferrous and Non-Ferrous foundry metallurgy, solidification science and technology, solidification processing of metals, alloys and composites, microgravity solidification, squeeze casting, die casting die design, heat treatment, Metallography, microstructure-property correlation ship, new materials and process development, aerospace engineering materials, computer simulation of casting solidification, FEM analysis and advanced engineering mathematics. Besides, he is a prominent writer and possesses wider experience in editing technical papers, theses and dissertations.

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