Chapter 1

CHAPTER 1

INTRODUCTION

• BACKGROUND OF ALUMINIUM METAL

Aluminum is the most abundant metal and the third most abundant element in the earth's crust, after oxygen and silicon. It makes up about 8% by weight of the earth’s solid surface. Aluminum is too reactive chemically to occur naturally as the free metal. Instead, it is found combined in over 270 different minerals. The chief ore of aluminum is bauxite, a mixture of hydrated aluminum oxide (Al2 O3.ᵪH2O) and hydrated iron oxide (Fe2 O3.ᵪH2O). Another mineral important in the production of aluminum metal is cryolite (Na3AlF6). However, cryolite is not used as an ore; the aluminum is not extracted from it.

Metallic aluminum was first prepared by Hans Oersted, a Danish chemist, in 1825. He obtained the metal by heating dry aluminum chloride with potassium metal.

AlCl3 + 3 K   →   Al  +  3 KCl

Robert Bunsen prepared aluminum metal in the 1850 by passing an electric current though molten sodium aluminum chloride. However, because both potassium metal and electricity were quite expensive, aluminum remained a laboratory chemical and a curiosity until after the invention of the mechanical electrical generator. In 1886, Charles Martin Hall of Oberlin, Ohio, and Paul Héroult of France, who were both 22 years old at the time, independently discovered and patented the process in which aluminum oxide is dissolved in molten cryolite and decomposed electrolytically. The Hall-Héroult process remains the only method by which aluminum metal is produced commercially.

Aluminum is a silvery-white metal with many valuable properties. It is light (density 2.70 g/cm3), non-toxic, and can be easily machined or cast. With an electrical conductivity 60% that of copper and a much lower density, it is used extensively for electrical transmission lines. Pure aluminum is soft and brittle, but can be strengthened by alloying with small amounts of copper, magnesium, and silicon. Based on its chemical reactivity, aluminum should not be very useful at all. Its standard reduction potential is –1.66 volts, indicating that it is a very good reducing agent. It is far more active than iron, which has a reduction potential of –0.44 volt. Aluminum withstands far better than iron, however, because the product of its corrosion, Al2O3, adheres strongly to the metal's surface, protecting it from further reaction. This is quite different from the behavior of iron's corrosion product, rust. Rust flakes off the surface of iron, exposing the surface to further corrosion. The protective oxide coating on aluminum is frequently enhanced by the process of anodization. Recycling of aluminum saves considerable energy. Because the aluminum is already in the metallic state, all of the energy spent in purifying the ore and reducing it to the metal is saved when aluminum is recycled. The aluminum needs only to be melted to be reused.

1.1.1 Properties of Aluminium

1. Light weight and high strength: Aluminium is a very light metal. The specific weight of aluminium is 2.7g/cm2 which is one third of steel. So it is used where we need light weight structure with a large strength. The energy consumption of aluminium metal is very low and load capacity is high.
2. High electrical and thermal conductivity: Aluminium material has high electrical and thermal conductivity. It is two times more conductive than copper and has light weight. It is used for the transmission of power for a long distance.
3. High corrosion resistance: Aluminium is a corrosion resistive material. It is due to the reason that when aluminium reacts with air it forms an oxide layer which acts as a protective layer.
4. Non-toxic and odorless: Aluminium is a non-toxic metal. It can be converted up to 0.0065mm thin foil for commercial use. So it is used to make cans, aluminium foils and packing sheets for protection of food or pharmaceutical.
5. Heat and light reflectivity: Aluminium is a good reflector of heat as well as light. It has low weight so it is used for making fire rescue blankets.

• Aluminium Alloys

When aluminium metal is modified according to the need of the challenges of advancing technology then it is called aluminium alloys. The alloy of a metal is contained better properties than the pure metal. Aluminium alloys are the alloys in which aluminium metal is base metal and some other elements are added into it to improve its properties. These alloying elements are Copper, Manganese, Silicon, Magnesium, and Zinc according to required applications of the metal alloy. There are two types of alloys casting alloys and wrought alloys, both of these types are subdivided into the categories of heat treatable and non-heat treatable. Aluminium alloys are widely used in engineering structures and components where light weight and corrosion resistance is required.

• Classification of Aluminium Alloys

1. Wrought Aluminium Alloys: - These are the alloys which are manufactured by pressing or hammering process. In this process pure aluminium and alloying elements are pressed or hammered together to make aluminium alloy.
2. Cast Aluminium Alloys: - These are the alloys which are manufactured by casting processes. In this process aluminium is melted in the furnace and the elements according to the composition required are mixed in melted aluminium. Then this melted mixture of metals is casted in to the required shape.

• Designation system of Wrought Aluminium Alloys
• First digit - Principal alloying constituent(s)
• Second digit - Variations of initial alloy
• Third and fourth digits - Individual alloy variations (number has no significance but is unique)

Table 1.1: Designation of wrought Aluminium Alloys

• Designation System of Cast Aluminium Alloys

• First digit -Principal alloying constituent(s)
• Second and Third digits - Specific alloy designation (number has no significance but is unique)
• Fourth digit - Casting (0) or ingot (1,2) designation

Table 1.2: Designation of Cast Aluminium Alloys

• Characteristics and applications of Wrought Alloys
  1. 1xxx - Pure Al
• Strain harden able
• High formability, corrosion resistance and electrical conductivity
• Electrical, chemical applications
• Typical ultimate tensile strength range: 10-27 ksi

The 1xxx series represents the commercially pure aluminium, ranging from the baseline 1100 (99.00% min. Al) to relatively purer 1050/1350 (99.50% min. Al) and 1175 (99.75 % min. Al). Some of them like 1350 which is used especially for electrical applications, has relatively tight control on those impurities that might lower electrical conductivity. The 1xxx series are strain-hardenable, but would not be used where strength is a prime consideration. Rather the emphasis would be on those applications where extremely high corrosion resistance, formability and/or electrical conductivity are required, e.g., foil and strip for packaging, chemical equipment, tank car or truck bodies, spun hollowware, and elaborate sheet metal work.

1. 2xxx - Al-Cu Alloys

• Heat treatable
• High strength at room & elevated temperatures
• Aircraft, transportation applications
• Representative alloys:2014,2017, 2024,2219,2195
• Typical ultimate tensile strength range:27-62 ksi

The 2xxx series are

Impressum

Verlag: BookRix GmbH & Co. KG

Tag der Veröffentlichung: 26.02.2018
ISBN: 978-3-7438-5831-2

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