What effect does annealing steel and aluminum alloys have on internal stress?

Annealing is a heat treatment process used to reduce hardness, improve ductility, and relieve internal stresses in metals such as steel and aluminum alloys. During annealing, materials are heated to a specific temperature and then cooled slowly, allowing atoms to rearrange into a more stable configuration. This process effectively alleviates the internal stresses that may have developed during previous fabrication processes, such as welding, casting, or cold working.

In the case of steel and aluminum alloys, the reduction of internal stress is crucial as these stresses can lead to warping, dimensional changes, or even failure of the material under load. By annealing, the material's microstructure becomes more uniform, resulting in improved mechanical properties and performance. Thus, the primary effect of annealing is indeed a decrease in internal stress. This allows for more reliable and predictable behavior of the material in subsequent applications.