Precipitation hardening, or age hardening, is a heat treatment process that increases the 屈服强度 of malleable materials. It involves heating an alloy to dissolve solute elements (solutionizing), rapidly cooling (quenching) to trap them in a supersaturated solid solution, and then aging at a lower temperature to allow fine particles of a second phase (precipitates) to form, which obstruct dislocation movement.
阿尔弗雷德·威尔姆 (Alfred Wilm) 偶然发现了沉淀硬化现象。在研究一种含铜、镁和锰的铝合金（后来命名为 Duralumin）时，他注意到即使在室温下，其硬度也会在淬火几天后增加。现在人们认为这种现象分为三个步骤。首先，在固溶处理中，将合金加热到足够高的温度，使所有溶质原子溶解成单相固溶体。其次，将合金在水等介质中快速淬火，使原子冻结在原地，形成过饱和固溶体。这种状态在热力学上是不稳定的。第三，在时效过程中（室温或高温），过饱和溶质原子扩散并聚集在一起，形成极小、连贯的新相颗粒，称为沉淀物。
These precipitates act as powerful obstacles to the movement of dislocations, which are the primary carriers of plastic deformation in crystalline materials. The effectiveness of the strengthening depends on the size, shape, and distribution of these precipitates. Initially, as precipitates form and grow, the strength increases. However, if the aging process continues for too long (over-aging), the precipitates become too large and lose coherency with the matrix, allowing dislocations to bypass them more easily, which leads to a decrease in strength. This process allows for the precise tailoring of an alloy’s mechanical properties.
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