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Precipitation hardening is a technique that strengthens malleable materials by creating solid impurities that halt dislocation movement. Alloys such as aluminum, magnesium, nickel, and titanium are used. The process involves heating the material, quenching it, and aging it. Impurities disrupt the crystal lattice structure, increasing yield strength. Alloys produced through precipitation hardening are used in high-temperature situations, such as pressure vessels and turbochargers.
Precipitation hardening, also known as age hardening, is a technique in which heat is applied to a malleable material, such as a metal alloy, to strengthen it. The technique hardens the alloy by creating solid impurities, called precipitates, which halt the movement of dislocations in the crystal lattice structure. Dislocations are the primary cause of a material’s plasticity; thus, the absence of dislocations increases the yield strength of the material. Alloys typically used include aluminum, magnesium, nickel, and titanium alloys.
Creating precipitation-hardened materials begins with heating the material to a very high temperature to dissolve the precipitate. It takes 1 hour to 20 hours for the precipitate to completely dissolve. The new mix then becomes supersaturated and is ready for further processing.
Supersaturation of the solution is achieved by quenching. Quenching can be completed in water, air, or a mixture of air and water. As an important step in solid solution strengthening, it leaves the material softer and better prepared for the subsequent precipitation hardening step.
After the initial phase and the quench phase, the solution is aged. Artificial aging occurs by heating the solution above room temperature and then allowing it to soak for 2-20 hours. The aging temperature and soaking time are determined by the desired strength of the final product. It is important to pay close attention to both temperature and time, because too high a temperature and excessive immersion can lead to less precipitates which decrease strength and increase ductility.
Natural aging is another option. If you decide to use this option, keep in mind that the natural aging of a solution takes much longer than the method mentioned above. It can take from a few days to several weeks.
Impurities produced through the precipitation hardening process disrupt the crystal lattice structure in stainless steel, aluminum and other alloys. They inhibit dislocations in these structures which make it more difficult for loose particles to cut through the material. Inhibiting these breaks is the key to increasing the yield strength of the alloy over time.
Alloys produced by precipitation hardening have many practical uses in the manufacturing industry. They are usually used to make parts that must withstand high temperature situations, such as parts of a pressure vessel or a turbocharger. Many alloys have very important uses in industry. Silicon is used to make semiconductor materials. Copper is used for a wide variety of purposes, from shipbuilding to roofing.
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