MATERIALS AND METALLURGY - NON-FERROUS ALLOYS

 

Non-ferrous Alloys

An alloy is a mixture of two or more materials, at least one of which is a metal. Alloys can have a microstructure consisting of solid solutions, where secondary atoms are introduced as substitutional or interstitials in a crystal lattice. An alloy may also be a mixture of metallic phases (two or more solutions, forming a microstructure of different crystals within the metal). Examples of substitutional alloys include bronze and brass, in which some copper atoms are substituted with either tin or zinc atoms, respectively.

Interstitial alloys are a compound formed when an atom with a small enough radius sits in an interstitial “hole” in a metal lattice. Examples of small atoms are hydrogen, boron, carbon, and nitrogen.

Solid solutions have important commercial and industrial applications, as such mixtures often have superior properties to pure materials. Many metal alloys are solid solutions. Even small amounts of solute can affect the electrical and physical properties of the solvent. Alloys are usually stronger than pure metals, although they generally offer reduced electrical and thermal conductivity. Strength is the most important criterion by which many structural materials are judged. Therefore, alloys are used for engineering construction.

Non-ferrous alloys do not contain iron (ferrite) in appreciable amounts; thus, they are based on non-ferrous metals (i.e., aluminum, gold, nickel, silver, tin, lead, zinc, etc.) Other common properties of non-ferrous metals are non-magnetic, malleable, and lightweight. Alloy systems are classified according to the base metal or specific characteristics that a group of alloys shares.

Also, non-ferrous alloys can be heat treated to alter the properties of strength, ductility, toughness, hardness, or resistance to corrosion. Many phenomena occur in metals and alloys at elevated temperatures. For example, recrystallization and precipitation. These are effective in altering the mechanical characteristics when appropriate heat treatments or thermal processes are used. The use of heat treatments on commercial alloys is an exceedingly common practice. Common heat treatment processes include annealing, precipitation hardening, quenching, and tempering. For example, quenching is the process of cooling a metal rapidly. This is most often done to produce a martensite transformation. This will often produce a harder metal in ferrous alloys, while non-ferrous alloys will usually become softer than normal.

Types of Non-ferrous Alloys

As was written, alloy systems are classified according to the base metal or to some specific characteristic that a group of alloys shares.

• Aluminum Alloys
• Copper Alloys
• Magnesium Alloys
• Titanium Alloys
• Nickel Alloys
• Lead Alloys
• Tin Alloys
• Zinc Alloys
• Zirconium Alloys

Another method is to group alloys by key application properties, such as density, corrosion resistance, melting point, etc.

• Light metals (aluminium, magnesium, and titanium)
• Corrosion-resistance alloys (cobalt, copper, nickel, titanium, aluminium)
• Superalloys (nickel, cobalt, iron-nickel)
• Refractory metals (molybdenum, niobium, tantalum, and tungsten)
• Low-melting-point metals (tin, bismuth, indium, lead, zinc)
• Reactive metals (titanium and zirconium)
• Precious metals (gold, silver, platinum, palladium, iridium, rhodium, ruthenium, and osmium)