Learn About Precipitation Hardening

Precipitation Hardening
••• Image copyright: University of Nevada, Reno

Precipitation hardening, also called age or particle hardening, is a heat treatment process that helps make metals stronger. The process does this by producing uniformly dispersed particles within a metal's grain structure that help hinder motion and thereby strengthen it—particularly if the metal is malleable.

The Precipitation Hardening Process

The details of how the precipitation process works can seem a bit complicated, but a simple way of explaining it is looking generally at the three steps that are involved: solution treatment, quenching, and aging.

  1. Solution Treatment: You heat the metal to a high temperature and treat it with a solution.
  2. Quenching: Next, you quickly cool down the solution-soaked metal.
  3. Aging: Finally, you heat the same metal to a medium temperature and cool it quickly again.

The result: A harder, stronger material.

Precipitation hardening is typically performed in a vacuum, inert atmosphere at temperatures ranging from between 900 degrees and 1150 degrees Farenheit. The process ranges in time from one to several hours, depending on the exact material and characteristics

As with tempering, those who perform precipitation hardening must strike a balance between the resulting increase in strength and the loss of ductility and toughness. Additionally, they must be careful not to over-age the material by tempering it for too long. That could result in large, spread out, and ineffective precipitates. 

Metals Treated by Precipitation 

Metals that are often treated by precipitation or age hardening include:

  • Aluminum—This is the most abundant metal in Earth's crust and the chemical element of atomic number 13. It does not rust or magnetize, and it's used for many products, from soda cans to vehicle bodies.
  • Magnesium—This is the lightest of all metal elements and the most abundant one on the surface of the Earth. Most magnesium is used in alloys, or metals that are made by combining two or more metal elements. Its applications are vast, and it's widely used in major industries, including transportation, packaging, and construction.
  • Nickel—The chemical element of atomic number 28, nickel can be used in everything from food preparation to building high-rise buildings and transportation infrastructures.
  • Titanium—This is a metal that's often found in alloys, and it has a chemical element of atomic number 22. It's used widely in the aerospace, military, and sporting goods industries due to its strength, resistance to corrosion, and light weight.
  • Stainless steels—These are actually alloys of iron and chromium that are resistant to corrosion. 

Other alloys—again, these are metals made by combining metal elements—that are hardened by precipitation treatments include: