Resistant Materials Metals These icons indicate that teacher’s notes or useful web addresses are available in the Notes Page. This icon indicates that the slide contains activities created in Flash. These activities are not editable. For more detailed instructions, see the Getting Started presentation. 1 of 17 © Boardworks Ltd 2005

Learning objectives Learning objectives To know where metals come from and how they are obtained. To understand the differences between, and properties of, ferrous and non-ferrous metals and alloys. To understand how the properties of different metals make them suitable for different uses. To know how the properties of metals can be altered by heating. Learning objectives 2 of 17 © Boardworks Ltd 2005

Where do metals come from? Metals are part of the earth’s crust. Economic, chemical and technological problems have to be solved to obtain them. How desirable a metal is often depends on how scarce it is. Gold diggers dig up tonnes to obtain a few grams, whereas there is so much iron that materials technologists are only interested if they can obtain hundreds of kilograms from each tonne of ore.

Where do metals come from? Pure metals like copper form part of the earth’s crust as metal ore. Copper ore is mined, then washed to remove other minerals and unwanted materials. It is heated in a furnace and the molten copper is run off. This process is known as smelting. As we moved towards the Iron Age, the ease with which metals could be shaped together with their strength made them invaluable. Initially small pieces of gold and copper were found and could be used without much processing, but these were used mainly for decorative purposes. To gather any significant amounts of metals, mining was needed. For example, copper was extracted from the mixture of minerals, rocks and dirt known as copper ore. This meant that lots of copper could be used in the production of household products such as pans and spears. While iron and copper are extracted by smelting, aluminium is extracted from the ore using electrolysis.

Extracting metals – smelting

Extracting metals – electrolysis Aluminium is the most plentiful metal found in the earth’s crust, and is in high demand because it is both light and strong. Aluminium is extracted from aluminium oxide (bauxite) by electrolysis. Electricity passes between the electrodes and pure aluminium forms at the cathode. carbon anode cathode lining molten aluminium metal

Ferrous and non-ferrous metals Metals can be classified into three groups: ferrous metals, non-ferrous metals and alloys. Ferrous metals are metals which contain iron. They will corrode if unprotected. Ferrous metals will be attracted by a magnet. Non-ferrous are metals which do not contain iron. Pure metals such as aluminium, copper, tin and lead are non-ferrous, and do not rust. Alloys are metals which are a mixture of two or more metals, benefiting from the properties of both. For example, brass is an alloy of copper and zinc.

Types of metals

Examples of ferrous metals The more carbon added to steel, the harder the alloyed steel. Unfortunately, when we add carbon to steel, this reduces the ductility and malleability of the material. There will always be a trade-off between hardness and brittleness when combining carbon with steel. However, there are several processes such as case-hardening, hardening, tempering, normalising and annealing which can be employed to counteract some of these properties.

Non-ferrous metals

Examples of alloys

Random alloy generator

Heat treatment – annealing While copper is heated to a full red, ferrous metals are heated to cherry red colour and then cooled very slowly. Aluminium is rubbed with liquid soap and heated until the soap turns black, then left to cool.

Heat treatment – hardening steel

Heat treatment – tempering

Market forms of metals Metals are commercially available in a range of stock shapes and sizes. flat strip round rod round tube square rod square tube hexagonal rod angle sheet octagonal rod channel

Key points Metals are extracted from the earth’s crust. Iron ore is smelted to obtain iron, while aluminium is obtained by electrolysis. Ferrous metals come from iron ore and include cast iron and steel. Non-ferrous metals include aluminium, copper and tin. Alloys such as brass and stainless steel are formed from two or more metals and other elements. Heating metals alters their properties. Annealing involves heating a metal and then allowing it to cool, which makes the metal more workable. Tempering steel makes it less brittle. Key points 17 of 17 © Boardworks Ltd 2005