Strengthening precipitation hardening

Al-Mg-Si alloys are strengthened by precipitation hardening in which MgjSi is formed. They are not very susceptible to stress-corrosion cracking which only occurs in specimens subjected to a high solution-treatment temperature followed by a slow quench Ageing such material eliminates susceptibility . 

Precipitates have important effects on the mechanical, electronic, and optical properties of solids. Precipitation hardening is an important process used to strengthen metal alloys. In this technique, precipitates are induced to form in the alloy matrix by carefully controlled heat treatment. These precipitates interfere with dislocation movement and have the effect of hardening the alloy significantly. 

This complex form of precipitation in the Al-Cu system is of great practical importance. The finely dispersed precipitates act as effective barriers to the glide movement of dislocations during plastic deformation and harden and strengthen the material. This has led to the development of a number of widely used precipitation-hardened Al-Cu alloys [1]. 

Strengthened by aging or precipitation hardening (Types 17-14 CuMo,17-10P, HNM)... 

How does precipitation hardening work to strengthen the material ... 

At half of the solidus temperature on the absolute temperature scale (i.e., 1850°C for tungsten), solid-solution alloys lose much of their strength, and dispersion-strengthened or precipitation-hardened alloys are significantly stronger and creep resistant. This is caused by the interaction between the dispersoids and dislocations, as well as subgrains and grain boundaries. 

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