Metal is malleable. It may not seem like it, since you can’t pick up a steel beam and bend it into a pretzel without help from machinery, but that doesn’t mean it’s as rigid and strong as we think it is! In fact, metal malleability is cause for concern in many instances where the intended application of metal needs to stand up to tremendous pressure in extreme conditions—conditions that might compromise the very structure of metal if not heat treated and reinforced appropriately.
One such heat treatment that’s used to increase yield strength in particularly malleable metals or metals intended for extreme conditions is precipitation strengthening in Gastonia, NC. This method—also referred to as “age hardening” in some circles—is generally focused on aluminum alloys, however it can encompass a bevy of other non-ferrous alloys as well, including copper, beryllium, tin and magnesium alloys.
Precipitation strengthening is named for the precipitate that is created during the impurity phase of the heat treatment. Essentially, the crystal lattice structure of a metal is being affected in such a way that it prevents shifts, stunting dislocations on the surface of the metal. The actual process is much more refined:
- The process begins with heat treatment, wherein an alloy is heated to an appropriate temperature somewhere in the range of its solvus and solidus temperatures. The temperature is held there until the metal reaches a uniform solid-solution state and its structure is homogenized.
- Next, the homogenized metal is quenched in order to induce rapid cooling. Because of the rapidity of this quenching, the solute is unable to be diffused and instead, it supersaturates, helping the alloy retain its homogenized structure below its reactive temperature.
- In the final step—the impurity phase—precipitates are formed from the supersaturated alloy. These precipitates impede dislocations in the crystal lattice structure of an alloy, thus reinforcing it and adding intended strength.
The chief objective of precipitation strengthening in Gastonia, NC is to exceed the basic solubility limit of an alloy to induce precipitate growth, thus creating hardening! Within the precipitate hardening process itself, there are actually two paths that can be taken: natural and artificial aging:
- When an alloy is left to precipitate at room temperature, it’s called natural aging.
- When an alloy is left to precipitate at a high temperature, it’s called artificial aging.
Natural and artificial aging can affect the finished hardness of the alloy depending on its composition, and are used depending on whether or not additional machining is required after the precipitation hardening process. Also, some alloys will not naturally age—they require a higher temperature, thus making them only fit for artificial aging.
So, where is precipitation hardening going to be most beneficial in terms of application? The best example is within the aerospace industry, where lightweight aluminum alloys are a staple of manufacturing. Aluminum alloys are the perfect cornerstone of aerospace engineering, however as they’re pushed to their limits, they require a strengthened composure to rely on to keep them performing—thus, precipitation strengthening is key!