The composition of a metal, meaning the elements it contains and their proportions, is what ultimately determines its group, properties, and applications. On the basis of composition, metals are generally classified into three groups: ferrous metals, non-ferrous metals, and alloys.
The ferrous group is composed mainly of iron. Small amounts of other metals or elements, such as carbon, manganese, nickel, chromium, silicon, titanium, and tungsten, may be added to achieve the required properties. Non-ferrous metals, by contrast, contain no iron. The common pure metals include aluminum, copper, lead, zinc, tin, silver, and gold. An alloy is a new metal formed by mixing two or more metals, and sometimes other elements, together. The most widely used metals overall include iron, aluminum, copper, titanium, zinc, and magnesium.
Iron is the basic component of steel. When carbon, a nonmetal, is added to iron in amounts up to 2.1%, the result is an alloy known as steel. More broadly, steel is an alloy of iron and other elements such as carbon, manganese, phosphorus, sulfur, nickel, chromium, tungsten, niobium (columbium), and titanium. Each element added to the iron base influences the properties of the steel, and these alloying additions are responsible for many of the differences between the various types and grades of steel.
Based on carbon content, steels are divided into three main groups. Low-carbon steels include grades from AISI 1005 to AISI 1026, along with IF, HSLA, TRIP, and TWIP steels. Medium-carbon steels range from AISI 1029 to AISI 1053, and high-carbon steels range from AISI 1055 to AISI 1095.
Under the EN standard, steel grades are instead divided into several groups: non-alloy steels (for example, EN DC01 to DC06, S235, and S275), alloy steels (for example, 20CrMo4 and 25CrMo4), stainless steels, tool steels (for example, DIN-EN 1.1545, AISI/SAE W110, and DIN-EN 1.2436 or AISI/SAE D6), steels for sheet and strip, and steels for electrical sheet and strip (for example, EN 1.0890 and EN 1.0803).
The aluminum industry uses aluminum in the form of cast and wrought aluminum alloys. These two classes can be further subdivided into families based on chemical composition and temper designation. According to the commonly accepted CEN standard designation system, the most common aluminum grades fall into the following series:
Titanium alloys are grouped less by a single element and more by the balance of properties their composition delivers. Adjusting the alloying additions, chiefly aluminium, vanadium, molybdenum, tin, zirconium, and palladium, shifts the metal toward one of three practical categories: corrosion resistance, high strength, or high-temperature performance.
The corrosion-resistant group is built around commercially pure titanium (grades 1 to 4) and lightly alloyed variants that add small amounts of palladium or molybdenum and nickel to improve resistance in aggressive chemical environments. Because strength is not the priority here, these compositions stay close to pure titanium. Typical examples include the Ti-Pd grades (7, 11, 16, and 17) and Ti-0.3Mo-0.8Ni (grade 12), which are favoured for chemical processing and marine service.
The high-strength group introduces larger quantities of aluminium and vanadium, and often molybdenum, chromium, or tin, to raise mechanical strength for structural and load-bearing use. The workhorse of this group, and of the titanium industry as a whole, is Ti-6Al-4V (grade 5). Other examples include Ti-6Al-6V-2Sn, Ti-10V-2Fe-3Al, and Ti-15V-3Cr-3Sn-3Al, all developed to deliver high strength while keeping titanium's characteristic low weight.
The high-temperature group is engineered to retain strength and resist creep at elevated temperatures, which makes these alloys suited to engine and other hot-section components. Their compositions typically combine aluminium and tin with zirconium, molybdenum, and small silicon additions that improve high-temperature stability. Representative grades include Ti-6Al-2Sn-4Zr-2Mo, the IMI series such as IMI 685 and IMI 834, and TIMETAL 1100.
The purity, or fineness, of gold in jewelry is indicated by its karat number. 24 karat (24K) gold is the purest classification of jewelry gold. Also known as fine gold, it is greater than 99.7% pure. Proof gold is even finer, at more than 99.95% purity, but it is used only for standardization purposes and is not available for jewelry.
The most widely used forms of copper and its alloys are brasses and bronzes. A brass is a copper-zinc alloy containing between 5% and 42% zinc, such as CuZn28, CuZn37, and CuZn42. Its German name is Messing (for example, Ms58 equals CuZn42), and brasses are usually yellow in color.
A bronze is an alloy of copper with other metals. The most common is tin (for example, CuSn6, CuSn10, and CuSn14), followed by phosphorus (for example, PB1C, PB4C, PB3, and LPB1C) and manganese (for example, HTB1, HTB2, and HTB3), but bronzes may also contain aluminium (for example, AB1C and AB2C) and lead (for example, LG1C, LG2C, and LG3C).
Metal composition is only one part of understanding how materials are defined, compared, and selected. To build a complete picture, explore the related articles in our Metal series. Learn how the physical and mechanical behaviour of materials is described in Metal Properties, and learn more about how materials are sorted into families in Metal Grades. Understand the documents that define materials in Metal Specifications, and the agreed frameworks that govern them in Metal Standards. Finally, discover how designations from different systems are matched to one another in Metals Equivalent and Cross-Referencing. Together, these guides connect composition, properties, grades, specifications, standards, and equivalency into a single, interlinked reference.
Metals are classified by composition into three groups: ferrous metals, which are based mainly on iron; non-ferrous metals, which contain no iron; and alloys, which are formed by combining two or more metals or elements. The specific elements present, and their proportions, determine each metal's properties.
Adding carbon to iron in amounts up to 2.1% produces steel. Carbon content is used to define three main groups: low-carbon steels (AISI 1005 to 1026), medium-carbon steels (AISI 1029 to 1053), and high-carbon steels (AISI 1055 to 1095). Other elements, such as manganese, chromium, and nickel, further modify the properties.
Aluminum is used as cast and wrought alloys, which are subdivided into series based on their main alloying elements, from the 1xxx series (essentially pure aluminum) through to the 8xxx series. Each series offers a distinct balance of properties.
Brass is a copper-zinc alloy containing between 5% and 42% zinc and is usually yellow in color. Bronze is an alloy of copper with other metals, most often tin, but also phosphorus, manganese, aluminium, or lead.
The karat number indicates the purity, or fineness, of gold. 24 karat (fine) gold is more than 99.7% pure, making it the purest classification used in jewelry. Proof gold, at over 99.95% purity, is used only for standardization and is not available for jewelry.