Aluminum alloy forging production is one of the main processing methods to provide mechanical parts blanks in the mechanical manufacturing industry. By forging, not only the shape of mechanical parts can be obtained, but also the internal structure of metal can be improved and the mechanical and physical properties of metal can be improved. Generally, important mechanical parts with high stress and requirements are mostly manufactured by forging production method. For example, the shaft, rotor, impeller, blade, retaining ring, column of large hydraulic press, high-pressure cylinder, roller of rolling mill, crankshaft of internal combustion engine, connecting rod, gear, bearing, and artillery in national defense industry are all produced by forging. Therefore, forging production is widely used in metallurgy, mining, automobile, tractor, harvesting machinery, petroleum, chemical industry, aviation, aerospace, weapons and other industrial sectors, even in daily life, forging production also has an important position.

In a sense, the annual output of forgings, the proportion of die forgings in the total output of forgings, and the size and ownership of forging equipment reflect the industrial level of a country to some extent.

Coarse grain defects of aluminum alloy forging die forgings

1. Material of forgings

The probability of coarse grains in die forgings varies greatly with different aluminum alloy brands. Forgings of Al-Zn-Mg-Cu alloys are less prone to coarse grain defects, while forgings of Al-Cu-Mg and Al-Mg-Si alloys are more likely to have coarse grain defects.

2. Aluminum alloy forging process parameters and die temperature

(1) Select a reasonable final forging temperature.

If the final forging temperature is too low, the forgings are prone to coarse grains. Lanxi Tongli Aluminum Co., Ltd. claims that the final forging temperature must be strictly controlled, especially for aluminum-copper-magnesium series and aluminum-magnesium-silicon series alloys. For example, the final forging temperature of 2A11(LY11) alloy blade die forgings must be higher than 390℃, otherwise coarse grains will easily appear. Different materials of forgings have different requirements for final forging temperature, but all aluminum alloy die forgings are required to have a final forging temperature not lower than 370℃.

(2) The preheating temperature of the mold should not be too low.

Too low die temperature will accelerate the cooling rate of the metal in the die cavity, so that the deformation temperature of the metal is too low, which makes it difficult for the metal to fill the die cavity and may form coarse grains on the surface of the forging. The preheating temperature of the die is related to the forging shape and aluminum alloy brand, and it is generally required to be controlled at 300℃ ~ 400℃.

(3) the deformation degree should not be too small

Especially, the deformation degree of the last fire should not be too small. If the deformation degree is small, the recrystallization crystal nucleus is less and the incubation period is long, the die forgings will form coarse grains after reheating (or heat treatment). If the deformation degree is as small as the critical deformation degree (about 3% ~ 15%), the recrystallized grains will grow rapidly, resulting in coarse grain defects in forgings. It is necessary to strictly control the number of die forging heats and the reduction per heat in production, so as to avoid the forging being in a critical deformation state because of too many die forging heats and too small reduction at one time. Under the condition of ensuring that metal can finally fill the die cavity and meet the requirements of low streamline, the number of die forging fires should be reduced as much as possible.

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