Processing technologies: Forging temperatures

With aluminium alloys, the forming temperature is between 320 °C and 480 °C depending on the composition. The forging temperature range is, however, very narrow. With forging, the metalworking process itself results in heat being transferred to the metal. The temperature of the tool is thus determined on the basis of the (logarithm of the) degree of deformation and the rate of deformation.
Production of unusable forgings can result if the optimum forging temperature is not maintained. Exceeding the solidus temperature leads to irreversible damage to the microstructure as a result of melting at the grain boundaries: the metal becomes brittle.

age-hardenable (wrought) alloys can be forged at a higher (solution) temperature in order to use the forming process simultaneously as a heat treatment at the same time. The workpiece is quenched immediately after forging.

Insufficiently high temperatures lead to cracking and high stresses. The cavities of the die are not filled and the flow stress increases with decreasing temperature.
Heat treatment is a means by which the properties of a metal can be changed in a specific manner by modifying its microstructure In most cases, the aim is to increase strength.

The heat treatment of age-hardenable wrought alloys comprises solution heat treatment, quenching and natural or artificial ageing. In order to remove internal stresses and distortion after quenching, shaped parts are subjected to cold upsetting by 1 to 3 % to reach their final size.

Forging at temperatures near the solution temperature, which is only slightly higher than the normal forging temperature, demands very accurate temperature control because the alloys used have a very narrow solution temperature range. If this is exceeded, melting takes place at the grain boundaries. However, if the solution temperature is not reached, the required strength values are not achieved.