Metal annealing refers to a process used to soften certain types of metals. This is necessary to produce various parts or structures from hard metals. Softened metal is much easier to form and work with than hardened metal. In addition, the annealing process provides more flexibility and makes metals less prone to cracking or breaking under stress or vibration. Methods for annealing can vary according to the type of metal used.
When steel is created, it is hardened by heating and then quenching or rapidly cooling. This alters the molecular structure of the metal. When molecules change their structure, metal is softened. This is why hot materials are easier to work with than cold materials.
Metal annealing is commonly used for steel, as many grades have been specially hardened by heat treatment. During the process, steel is usually heated to the point of glowing red and then cooled off slowly. During the process of heating, steel molecules change alignment and when slowly cooled, the alignment is kept intact.
This metal annealing process requires a great deal of heat. It helps stainless steel reach its “glowing hot” condition and stay this way for several minutes. Some types of stainless steel require fast quenching or you will have problems with warping. The metal is kiln heated for an hour or so before quenching.
Unless copper is extremely clean and shiny, annealing will cause the formation of oxides. Copper is usually cleaned to make sure embedded oxides are removed, before metal annealing. However, because copper is an excellent thermal conductor, it heats rapdily. After heating, copper is quickly quenched, and this must be done as soon as possible.
Aluminum alloys are commonly used in the aircraft and aerospace industry. As a result, many of these metals are work hardened to give them the desired properties. However, once a piece is work hardened, it may need to be softened for machining or turning into a specific part. This is where the metal annealing process comes in.
Some types of aluminum alloys are unstable after cold hardening processes and aluminum annealing is used to return them to a more stable state. This can sometimes be done at low temperatures. 1100 aluminum is not difficult to anneal because the process can be as simple as heating and cooling off. This can often be done at the job site. However, alloys like 2024 must undergo a metal annealing process under a controlled environment, and this takes special equipment, or the aluminum may crack or break.