1. Large grain size in aluminum forging is often due to an excessively high initial forging temperature and insufficient deformation, or an overly high final forging temperature or deformation falling into the critical deformation zone. Excessive deformation in aluminum alloys can lead to texture formation; if the deformation temperature of the alloy is too low during high temperatures, it may also cause coarse grain size when forming a mixed deformation structure. Large grain size reduces the plasticity and toughness of the forging, and significantly decreases its fatigue performance.
2. Inconsistent grain structure; uneven grain structure in aluminum forging refers to the fact that some parts of the forging have particularly coarse grains, while other parts have very fine grains. The main cause of uneven grain structure is the uneven deformation of the billet, leading to varying degrees of grain breakage, or the deformation of certain local areas falling into the critical deformation zone, or localized work hardening in high-temperature alloys, or the coarsening of local grains during quenching heating. Heat-resistant steel and high-temperature alloys are particularly sensitive to grain non-uniformity. Inconsistent grain structure can significantly reduce the durability and fatigue resistance of the forging.
3. Chilling Phenomenon; During the deformation process, due to low temperatures, rapid deformation speed, or rapid cooling after forging, the recrystallization-induced softening does not keep pace with the deformation-induced strengthening (hardening), resulting in some cold deformation structures remaining in the forged workpiece after hot forging. The presence of these structures increases the strength and hardness of the forging but reduces its ductility and toughness. Severe cold hardening may lead to forging cracks.
4. Cracks; Aluminum forging cracks are usually caused by high tensile, shear, or additional tensile stresses during the forging process. Cracks typically appear in areas with high blank stress and thin thickness. If there are microcracks on the blank surface or internally, or if there are organizational defects within the blank, or if the material's plasticity is reduced due to improper heat treatment temperatures, or if the deformation speed is too fast and the degree of deformation is excessive, exceeding the material's allowable plasticity index, cracks may occur during rough machining, stretching, punching, boring, bending, and extrusion processes.
5. Cracking; Aluminum forging cracking is a type of shallow turtle-like crack on the forging surface. This defect is prone to appear on the surfaces subjected to tensile stress during forging (such as unfilled projections or bends). The internal causes of cracking can be multifaceted: an excess of fusible elements like Cu and Sn in the raw material. During prolonged high-temperature heating, copper precipitation on the steel surface, coarse surface grain, decarburization, or surfaces after multiple heatings. Excessive sulfur content in the fuel, with sulfur渗透 into the steel surface.
6. Flash Cracks; Flash cracks in aluminum forging are cracks that occur on the parting surface during the die forging and trimming processes. Possible causes for the flash cracks include: intense metal flow during die forging, leading to steel penetration. The cutting edge temperature for magnesium alloy die forgings is too low; for copper alloy die forgings, the cutting edge temperature is too high.
