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Pure aluminium is a relatively soft, ductile material. For most engineering applications it is alloyed with a range of materials to improve its properties.
Each alloy is given a four digit designation, depending on the main alloying element. For example, in the 4xxx series each alloy has silicon as the main alloying element. The 6xxx series are alloyed with magnesium and silicon.
Some alloying elements, such as copper, can make an alloy difficult, if not impossible, to weld.
Carbon steels cover a wide range of commonly-used engineering materials including the 'mild steels'.
The term 'carbon steels' is taken to include carbon-manganese steels, structural steels, HSLA steels and Q&T Steels which includes HY and QT types.
Galvanised and coated steels
Galvanised and coated steels are a very specific group of normally low-carbon steels, which have undergone a surface treatment either to improve a property (such as corrosion resistance) or to improve its appearance.
In a welding and cutting context, these coating materials can often create problems with both weld and cut quality, as well as health hazards due to the fumes created as they are vaporised.
Alloy steels are carbon and carbon manganese steels which have other alloying elements such as nickel, chromium and molybdenum added to them to improve their mechanical properties.
Low temperature alloy steels have small amounts of nickel added. Creep-resisting steels are alloyed with chromium and molybdenum. These steels are often used in high temperature environments such as steam boilers.
High manganese steels can contain 14% Mn, giving these materials high hardness which makes them suitable for applications such as the manufacture of railway lines.
Stainless steels are defined as steels containing more than 13% Chromium.
There are four basic categories of stainless steel.
The most common are the austenitic steels such as 316, and 304 alloys which contain both chrome and nickel.
Ferritic stainless steels are chrome-containing alloys with low levels of carbon such as 409 and 430 grades.
Martensitic stainless steels are also chrome-containing but have much higher levels of carbon. 410 and 416 are examples of these materials.
Duplex stainless steels have a mixed microstructure of ferrite and austenite and have the properties to match.
The main types of cast iron are:
- grey cast iron. This contains 2% to 4% carbon and over 2% silicon.
- white cast iron. This has the same range of carbon as grey but has less than 1% silicon.
- malleable cast irons. Heat-treated white cast iron.
- alloy cast iron. May be alloyed with chromium, nickel, molybdenum, and other elements to give specific strength, corrosion, or high temperature properties.
In its pure form, copper can be used as an engineering material; however, it is normally alloyed with other materials to improve its mechanical properties.
The most common alloys of copper are:
- brasses, in which zinc is the main alloying element.
- bronzes, which contain tin.
- cupro-nickels, which are nickel-containing alloys used mainly for their excellent salt water. corrosion properties.
Nickel alloys are used in a wide variety of applications, including;
- marine environments
- high temperature areas
Inconels and Nimonics are nickel chrome alloys, while Incoloys are nickel iron alloys.
Hastalloys are nickel, chrome and iron alloys, while Monels are nickel-rich copper-containing alloys.
Titanium is an attractive engineering material because of its low density, excellent corrosion resistance and the high strengths which can be obtained through alloying.
Its reactive nature, however, can cause problems when it is welded. Keeping oxygen levels very low is of fundamental importance.