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Four Kinds of Common Aluminum Forging Defects

There are usually four kinds of defects caused by improper forging process of aluminum alloy:

1. Large-grained

Due to too high initial aluminum forging temperature and insufficient deformation degree, or too high final forging temperature, or deformation degree fell into the critical deformation zone. Aluminum alloy deformation degree is too large, forming texture; Superalloy deformation temperature is too low, the formation of mixed deformation microstructure may also cause coarse grains.

The ductility and toughness of aluminum forgings will be reduced and the fatigue performance will be obviously decreased. Uneven grain size: refers to the fact that the grain size in some parts of the forging is particularly large and smaller in some parts. The main reason for the unevenness of grains is that the unevenness of deformation in different parts of the blank results in different degree of grain breakage, or the degree of deformation in local areas falls into the critical deformation zone, or the local processing hardening of superalloy, or the local coarse grains in quenching.Heat resistant steels and superalloys are particularly sensitive to uneven grain size. The unevenness of grain will obviously decrease the endurance and fatigue performance of aluminum forgings.

2. Cold Hard Phenomenon

During deformation, due to low temperature or too fast deformation speed, and too fast cooling after forging, the softening caused by recrystallization may not keep up with the strengthening (hardening) caused by deformation, so that part of the cold deformation structure remains inside the forging after hot forging.The existence of such structure improves the strength and hardness of forgings, but reduces the plasticity and toughness.Severe chiller may cause forging cracking.

3. Cack

The crack is usually caused by tensile stress, shear stress or additional tensile stress.The crack usually occurs at the place where the stress is greatest and the thickness is thinnest. If there are microcracks on the surface and inside of the blank, or there are structural defects in the blank, or improper thermal processing temperature reduces the plasticity of the material, or the deformation speed is too fast, the deformation degree is too large, exceeding the plastic pointer allowed by the material, etc., cracks may occur in the process of coarse drawing, long drawing, punching, expanding, bending and extrusion.

4. Chap

Chap is a shallow tortoise-like crack on the surface of the forging. This defect is most likely to occur on surfaces that are subjected to tensile stress during forging (for example, unfilled bulges or bent parts). The internal cause of cracking may be various: (1) raw material Cu, Sn and other fusible elements too much. (2) high temperature long time heating, steel surface precipitation, surface grain size, decarburization, or after multiple heating surface. (3) fuel sulfur content is too high, there is sulfur infiltration steel material surface.
 

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