Introduction to Metals 121

AISI-SAE number

The most common classification in the United States for plain carbon steels and alloy steels. American Iron and Steel Institute (AISI) is an association responsible for setting standards and creating numbering systems for various ferrous metals, and the Society of Automotive Engineers (SAE) writes specifications and other data used in a broad range of industries.

alloy

A metal consisting of a mix of two or more elements, one of which must be a metal. Steel is an alloy of carbon and iron.

aluminum

A nonferrous metal that is silvery white in color and lightweight. Aluminum resists corrosion and is a good conductor of electrical and thermal energy.

annealing

The steady heating of a metal above the recrystallization phase, followed by gradual cooling. Annealing can reduce hardness, improve machinablitiy, and facilitate cold working.

atoms

The smallest unit of an element. An atom consists of electrons orbiting around a center nucleus of protons and neutrons.

BCC

Body-centered cubic. The crystal structure that contains an atom in the center and one atom in each corner of a cube. BCC metals are often hard.

body-centered cubic

BCC. The crystal structure that contains an atom in the center and one atom in each corner of a cube. Body-centered cubic metals are often hard.

brittle

A material's unwillingness to be drawn, stretched, or formed. Brittle materials tend to fracture when subjected to these forces.

cast

A manufacturing process that pours a liquid material into a hollow mold until the material cools into a solidified shape. Casting is often used to form metals that are difficult to machine.

cast irons

An iron alloy usually containing more than 2% carbon, along with silicon and sulfur. Cast iron products are formed using molds and casting processes.

ceramic

A hard, brittle material that can withstand high temperatures and resist corrosion. Ceramics include traditional materials such as brick and clay, as well as advanced ceramics used as abrasives and cutting tools.

cold working

Any metal shaping process that takes place when the metal is below its recrystallization temperature. Cold working adds certain properties to the metal, such as increased strength and improved surface finish.

composite

A material made by combining materials from two or more of the following groups: metals, plastics, and ceramics. Composites can be laminar, particulate, or reinforced fibers.

compressive strength

The ability of a material to resist forces that attempt to squeeze or crush it. Compressive strength is the amount of compressive stress a material can withstand before fracturing.

copper

A nonferrous metal that is very ductile, thermally and electrically conductive, and corrosion resistant. Copper is often used to make electrical wiring.

corrosion

The gradual deterioration of a material due to atmosphere, moisture, chemicals, or other agents. Corrosion often appears on metal in the form of rust.

corrosion resistance

The ability of a material to resist deterioration and chemical breakdown due to surface exposure in a particular environment. Chromium and aluminum are materials with high corrosion resistance.

crystal structures

The regular, repeating pattern of atoms in a material. Metal crystal structures develop as the metal drops below the recrystallization temperature and solidifies.

ductility

The measure of a material's ability to be drawn, stretched, or formed without fracturing. Copper and aluminum are highly ductile metals.

electrical conductivity

The ability of a material to act as a medium for conveying electricity. Metals such as copper and aluminum have high levels of electrical conductivity.

electromagnets

A magnet formed from electric current. An electromagnet is typically formed by wrapping a current-carrying coil around an iron core.

electrons

A negatively charged particle that orbits the nucleus of an atom. Electrons are involved in chemical bonding and electrical conductivity.

face-centered cubic

FCC. The crystal structure that contains one atom in the center of the six sides of a cube and one atom in each corner of the cube. Face-centered cubic metals are often ductile.

FCC

Face-centered cubic. The crystal structure that contains one atom in the center of the six sides of a cube and one atom in each corner of the cube. FCC metals are often ductile.

ferrous metals

A metal in which iron is the main ingredient. The main groups of ferrous metals are cast iron and steel.

grains

An arrangement of atoms that creates a uniform, repeating structure. Grains are individual crystals in a metal.

graphite

A soft, black form of carbon. Excess carbon appears as flakes or spheres in cast irons and helps to dampen vibrations and improve machinability.

hardenability

The ability of a metal to be hardened by heat treatments or other processes. Steels have varying degrees of hardenability, depending on their alloying elements.

hardness

The measure of a material's ability to resist penetration, indentation, and scratching. In some metals, the level of hardness can be controlled through heat treating.

HCP

Hexagonal close-packed. The crystal structure that contains a collection of atoms that are closely packed into the shape of a hexagon. HCP metals are often brittle.

heat treating

The controlled heating and cooling process used to change the structure of a material and alter its physical and mechanical properties. Annealing, quenching, and tempering are heat treatments.

hexagonal close-packed

HCP. The crystal structure that contains a collection of atoms that are closely packed into the shape of a hexagon. Hexagonal close-packed metals are often brittle.

high-performance alloy

An expensive, complex metal alloy designed to perform under intense conditions, such as elevated temperatures. High-performance alloys are also known as superalloys.

I-beams

A structural support with a cross section resembling an 'I.' I-beams are usually made of steel.

lead

A nonferrous metal that is very soft, ductile, and heavy. Lead is a poor electrical conductor and is often used as a soldering alloy and sound dampener.

magnetism

The power of attraction and repulsion that exists in materials. Magnetism most often occurs between metals.

mechanical properties

A characteristic that describes how a material reacts when subjected to a force that attempts to stretch, compress, bend, dent, scratch, or break it. Ductility, hardness, and impact resistance are mechanical properties.

metal

A naturally occurring material with high electric and thermal conductivity, luster, density, and strength. Examples of metal include copper, iron, nickel, and lead.

nonferrous metals

A metal that does not contain iron as the main ingredient. Aluminum, copper, and zinc are nonferrous metals.

physical properties

A characteristic that describes a material's volumetric, thermal, electrical, and magnetic qualities. Physical properties describe how a material responds to forces other than mechanical forces.

plastic

A polymer material characterized by its light weight, high corrosion resistance, a high strength-to-weight ratio, and low melting point. Most plastics are easily shaped and formed.

pure metals

A metal that does not intentionally contain any other material. Pure metals are usually used as alloying elements in commercial applications.

quenching

The soaking of a metal at a high temperature above the recrystallization phase, followed by rapid cooling. Water, saltwater, air, and oil are common quenching mediums.

recrystallization temperature

The temperature at which new grains are formed in a metal. Every metal has a specific recrystallization temperature.

shear strength

The ability of a material to resist forces that attempt to cause the internal structure to slide against itself and separate. Shear strength is the amount of shear force a material can withstand before fracturing.

soldering alloy

A metal alloy that melts at relatively low temperatures and is used to join metal parts. Tin is commonly used as a soldering alloy.

steel

A ferrous metal consisting of iron and carbon, usually with small amounts of manganese, phosphorus, sulfur, and silicon. Steel is a popular, inexpensive commercial metal.

steels

A ferrous metal consisting of iron and carbon, usually with small amounts of manganese, phosphorus, sulfur, and silicon. Steels are popular, inexpensive commercial metals.

strength

The ability of a material to resist forces that attempt to break or deform it. A material exhibits tensile, compression, or shear strength, depending on the deforming force.

superalloy

An expensive, complex metal alloy designed to perform under intense conditions, such as elevated temperatures. Superalloys are also known as high performance alloys.

tempering

The heat treatment of metals to temperatures below the recrystallization phase, followed by gradual cooling. Tempering can increase a material's hardness.

tensile strength

The ability of a material to resist forces that attempt to pull apart or stretch it. Tensile strength is the amount of tensile stress a material can withstand before fracturing.

thermal conductivity

A physical property that indicates how well heat energy transfers through a material. Materials with low thermal conductivity make good heat insulators.

tin

A nonferrous metal that is very soft. Tin is often used as a plating metal and soldering alloy.

titanium

A nonferrous metal that is lightweight, corrosion resistant, and has a high strength-to-weight ratio. Titanium is often used in the aerospace industry.