Coherence (metallurgy)

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In metallurgy, coherence refers to the connection of the lattice structure of the precipitate to the material matrix. If the lattice constant for the same type of crystal deviates from the precipitate from the surrounding matrix by less than 2%, the lattice planes of the matrix can merge into those of the precipitate. If the precipitates and the matrix only have a few common lattice planes, one speaks of partial coherence. Incoherent precipitates do not have any common slip planes, which is why the dislocations supporting the deformation cannot intersect them (penetrate into these particles).

The coherence plays an important role in the hardening of aluminum alloys :

The targeted change in the structure of the material has significant effects on the strength properties of the alloys created by the embedded foreign metals. When it comes to aluminum, a distinction is made between non-hardenable and hardenable aluminum alloys.

Non-hardenable aluminum alloys are materials in which an increase in strength can only be achieved through cold forming . These are alloy types such as aluminum - magnesium , aluminum- manganese , aluminum-magnesium-manganese and aluminum- iron - silicon, as well as pure and pure aluminum.

Age-hardenable alloys are materials in which an increase in strength is achieved not only through cold forming but also through heat treatment. These include alloy types such as aluminum-copper-magnesium, aluminum-magnesium-silicon, aluminum-zinc-magnesium-copper, aluminum-silicon-magnesium, aluminum-copper-titanium and aluminum-copper-titanium-magnesium. The hardening processes are cold hardening by solution heat treatment and quenching and aging at room temperature, as well as hot hardening by aging at elevated temperature.

Furthermore, coherent precipitations play an important role in the electrical resistance of materials, as they influence the lattice parameters.