As you have already studied, metals are divided into two classes, ferrous and nonferrous. Ferrous metals are those in the iron class and are magnetic in nature. These metals consist of iron, steel, and alloys related to them. Nonferrous metals are those that contain either no, or very small amounts of, ferrous metals. These are generally divided into the aluminum, copper, magnesium, lead, and similar groups.
Although you will hardly ever work with pure metals, you need to be knowledgeable of their properties because the alloys you will work with are combinations of pure metals. Some of the pure metals discussed in this chapter are the base metals in these alloys, especially iron, aluminum, and magnesium. Other metals discussed are the alloying elements present in small quantities but important in their effect, including chromium, molybdenum, titanium, and manganese.
An alloy is a mixture of two or more elements in solid solution in which the main element is a metal. Most pure metals are either too soft, brittle or chemically reactive for practical use. Combining different ratios of metals as alloys modifies the properties of the resultant metals to produce desirable characteristics. The reason for making alloys is generally to create a less brittle, harder, corrosion resistant material, or one with a more desirable colour and luster.
Of the metallic alloys in use today, the alloys of iron (steel, stainless steel, cast iron, tool steel, alloy steel) make up the largest proportion by both quantity and commercial value. Iron alloyed with various proportions of carbon gives low-, mid- and high-carbon steels, and as the carbon levels increase, ductility and toughness decrease. The addition of silicon will produce cast irons, while the addition of chromium, nickel, and molybdenum to carbon steels (more than 10%) results in stainless steels.
Aluminum, titanium, copper, and magnesium alloys are also significant in commercial value. Copper alloys have been around since prehistory—bronze gave the Bronze Age its name—and have many applications today, most importantly in electrical wiring. The alloys of aluminum, titanium, and magnesium are valued for their high strength-to-weight ratios. These materials are ideal for situations where high strength-to-weight ratio is more important than material cost, such as in aerospace and some automotive applications.