What Are the Stages of Structural Changes in Die Forgings?

Sequence of structural changes in die forgings

During the forming process of large-scale die forgings, the softening process plays an important role in dynamic recovery, and the structure will also change. Then, in what order and shape will the die forging change? In the initial deformation stage of the die forgings, a substructure with high-density dislocations will be formed. These dislocations can be uniformly distributed or become brittle substructures at grain boundaries. Even in cold deformation, during the stage where the softening process is not obvious yet, this stage of hot deformation can be named as the stage of hot working hardening.

In the second stage of the structural changes in the die forging, due to the enhancement of the softening process, polygonal grain boundaries are formed, and the area inside the grain boundary of the sub-grain has relatively high free dislocation density. In the deformation process, the polygonal substructures gradually replace the hot working structure. The polygonal substructures themselves are also changing, resulting in nearly equiaxed sub-grains. At the end of the structural changes in the die forgings, the equiaxed polygonal substructure remains unchanged, and it continuously transforms with stress and metal substructures, corresponding to the rising part of the deformation diagram. In the next stage of hot deformation, stress and the final polygonal structure no longer change.

Hot deformation of die forgings

In the next stage of hot deformation, stress and the resulting polygonal structure no longer change. The center axis milling is mainly used in the process of the die forging ring, and it must be inserted into the drilled hole of the blank, and supported by the bracket and hammer to hit it during the die forgings, so that the blank is repeatedly die forged along the circumference between the center axis and the anvil until the inner diameter reaches the required size. After drilling two small holes on the blank, the metal is opened between the two holes.

By investigating and understanding several factors that affect the current production line of die forgings, the correct production process plan and die forging mold design plan for die forgings are obtained to achieve the best production line. After a series of comparative deformation experiments, the best die forging process system was determined and applied to production, thereby improving the mechanical properties of aluminum alloy blade die forgings.

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