Forging process of hot forged aluminum

Aluminium alloy forgings are aerospace, transportation, power energy, machinery manufacturing and other departments to make the key mechanical components indispensable received material, is very important in the national production and national defense in the special status as aerospace, modern transportation (especially modern cars and high speed rail, etc.), the development of new energy industry, In recent years, energy saving, environmental protection, safety and other requirements for the increase of lightweight, aluminum instead of steel, aluminum instead of copper, to forge casting has become the development trend - aluminum alloy forgings with low density, high specific strength and specific stiffness, corrosion resistance, fatigue resistance, processing performance and good performance characteristics, has been more and more widely used.

(1) The forging deformation temperature range is narrow

The forging deformation temperature of most aluminum alloys is 350 ~450T: within the range, the deformation temperature range is around lOOT, and the deformation temperature range of a few alloys is even only 50-70T; , the forging operation time is allowed to be short. This brings great difficulty to forging operation undoubtedly, for longer forging time, need to rely on the blank as far as possible heating to the upper limit temperature, increase the forging fire and will work, die preheating to a higher temperature.

(2) Sensitive to strain rate

Aluminum alloy is sensitive to strain rate, so it is necessary to select forging equipment with low and stable speed for forging. For ingot, in order to prevent forging crack, usually need to be in the state of compressive stress, low speed opening, the use of extrusion and forging or rolling, aluminum alloy die forging, often need to be carried out in hydraulic or mechanical press, as far as possible not to forge hammer forging equipment progress, forging equipment choice is relatively small.

(3) Strict requirements for heating and forging temperature

Due to the narrow deformation temperature range of aluminum alloy forging, in order to prolong the forging operation time, it should be heated to the upper limit of the deformation temperature, which requires the use of high-precision heating furnace and temperature control instrument to control the heating temperature; Otherwise, it is easy to overheat. Most of the aluminum alloy semi-finished products have high plasticity and are not easy to crack under normal circumstances; But should avoid intense deformation in the process of forging, so as to avoid high temperature rise and influence of forgings groups and performance, if you don't pay attention to the operation, adopting high speed (such as the use of forging hammer) and large deformation of the forging, large amounts of deformation can transform heat energy has the potential to forging temperature than forging temperature limit, causes the burnt, and cause the microstructure and mechanical properties of forgings is unqualified.

(4) Good thermal conductivity

The thermal conductivity of aluminum alloy is 3 ~4 times that of steel, and its advantage is that the blank does not need to preheat, it can be directly installed in the high temperature furnace heating; But the disadvantage is that the surface heat dissipation is too fast in the forging process, resulting in the forging process inside and outside the temperature difference is too large, so that the deformation is not uniform, leading to local critical deformation, easy to cause the forging local coarse crystal, so that the forging organization is not uniform. In most aluminum alloys, especially the aluminum-manganese alloy with extrusion effect, the common coarse crystal ring on the surface of the extruded bar may be related to the fast heat dissipation and high friction on the surface of the blank, and the uneven deformation of the inner and outer layers falling into the critical deformation zone. To prevent rapid heat loss, the die and the tool in contact with the workpiece must be preheated to a temperature of 300T or higher.

(5) Large friction coefficient and poor liquidity

The friction coefficient between aluminum alloy and steel die is large, and the fluidity is poor during deformation, which makes it difficult for the metal to fill the die groove during die forging. It is usually necessary to increase the working step and die, and increase the radius of the round corner of the die.

(6) High adhesion

Aluminum alloy viscosity is large, when intense deformation forging, blank will often bond on the mold, easy to cause defects such as forging skin, warping, but also cause mold wear, serious will lead to forging and die both scrap.

(7) Strong crack sensitivity

Aluminum alloy is sensitive to cracks. If the cracks produced in the forging process are not cleaned up in time, they will expand rapidly in the subsequent forging, resulting in the scrap of the forging.