[China Aluminum] coarse-grained defects are one of the common defects in aluminum alloy die forgings, which reduces the strength of the forgings. In the coarse-grained structure in the forging and the transition zone from the coarse-grained structure to the fine-grained structure, the fatigue strength of the forging decreases [1-2]. This article mainly discusses the measures to avoid and reduce coarse grain defects in the production process of aluminum alloy die forgings.
A coarse-grained appearance of the mechanism metal after the plastic deformation of the free energy increases, the organization is in an unstable state, when it is heated to a suitable temperature, the nucleus is re-formed and grow, the microstructure consisting of new grains called recrystallization. Fine and uniform equiaxed grains are generally obtained after recrystallization, but if the heating temperature is conducive to grain growth or the heating and holding time is too long, the recrystallized grains will grow into coarse grains [3-4]. Grain growth process can be divided into two types: one is to gradually grow up, showing the relative size of each grain is basically close; the other is an abnormal growth, manifested as between each grain The relative sizes are very different, and some grains grow very thick. In the coarse-grained defects of aluminum alloy die forgings, there is a greater chance that the recrystallized grains will grow abnormally.
2 Avoid or reduce coarse-grain defects in die forgings Coarse-grain defects in aluminum alloy die forgings are related to forging material, forging process parameters, forging shape, die temperature, and heat treatment process parameters.
2.1 Forging Material The manufacturing of die forged aluminum has a different winning combination number, and there is a great difference in the probability of coarse crystals appearing in the product. For aluminum-zinc-magnesium-copper alloys, coarse-grain defects are less likely to occur in forgings, while aluminum-copper-magnesium, aluminum-magnesium-silicon alloys and forgings have relatively more chances of coarse-grain defects.
2.2 Forging process parameters and mold temperature (1) Select a reasonable final forging temperature Final forging temperature is too low then the forgings are prone to coarse grain, especially the aluminum - copper - magnesium, aluminum - magnesium - silicon alloy must be strictly controlled end Forging temperature, such as the final forging temperature of 2A11 (LY11) alloy paddle forgings must be higher than 390 °C, otherwise it is easy to appear coarse crystal. Forgings of different materials on the final forging temperature requirements are different, but all of the aluminum alloy die forgings require the final forging temperature of not less than 370 °C.
(2) Mold preheating temperature should not be too low Mold temperature is too low will accelerate the cooling rate of metal in the cavity, so that the metal deformation temperature is too low, so that the metal is difficult to fill the cavity and may form coarse crystals on the surface of the forgings. The preheating temperature of the mold is related to factors such as the shape of the forging and the aluminum medal, and the general requirement is to control the temperature from 300°C to 400°C.
(3) The degree of deformation should not be too small, especially the degree of deformation of the later fire should not be too small. If the deformation is small, the number of recrystallized nuclei is small and the incubation period is very long. After the die forging is heated again (or heat treatment) It will form coarse grains. If the degree of deformation is within the critical deformation range (approximately 3% to 15% or so), the recrystallized grains will grow sharply, causing coarse crystal defects in the forgings. In the production, we must strictly control the die forging heat and the amount of each fire under the fire, to avoid the excessive number of forging fire, a small amount of reduction in the forging is in a critical state of deformation. In the case of ensuring that the metal can fully fill the mold cavity and low current flow requirements, the number of die forging fires should be minimized. The shape of a forging that is simple and easy to form can be formed in a single fire. Forgings with a complex shape and not easily formed, the forging heat should not exceed 3 times.
(4) The remaining amount of wool should not be too large. Especially for forgings with high ribs, if there is still excess metal left after the metal has filled the cavity, the upper and lower molds will continue to move closer, and the excess metal at the web will be along the ribs. The roots directly flow into the burr grooves in a closer path, which may cause local coarse crystals due to excessive deformation.
2.3 selection of heat treatment parameters Heat treatment when quenching temperature is too high, holding time is too easy to make aluminum alloy forging coarse grain. Especially for aluminum-magnesium-silicon and aluminum-copper-magnesium alloys, the quenching temperature and holding time must be strictly controlled.
Emergency, LED driver,Emergency Power
Fuonce Lighting , https://www.fuonce.com