(a) free forging; (b) die forging; (c) longitudinal rolling; (d) cross rolling; (e) cross rolling; (f) positive extrusion; (g) reverse extrusion; (h) drawing; (i) stamping; (j) bending
(1) The most common rolling method
According to the different rotation directions of the rolls, the aluminum alloy rolling can be divided into vertical rolling, cross rolling and cross rolling. Depending on the roll system, aluminum alloy rolling can be divided into two rolls (one pair) rolling, multi roll rolling and special roll systems (such as planetary rolling, V rolling, etc.) rolling. Depending on the shape of the rolls, aluminum alloy rolling can be divided into flat roll rolling and hole roll rolling. According to different product varieties, aluminum alloy rolling can be divided into plate, belt and foil rolling, bar, flat bar and profiled profile rolling, pipe and hollow profile rolling.
(2) The most common extrusion method
Extrusion is a plastic working method in which an external force is applied to a metal ingot contained in a container (squeezing cylinder) to flow out of a specific die hole to obtain a desired sectional shape and size. Several main extrusion methods widely used in the aluminum industry are: positive extrusion, reverse extrusion, pipe extrusion, continuous extrusion, and the like.
(3) The main forging method
Aluminum alloy forging has two basic methods: free forging and die forging. Free forging is to forge a workpiece between flat anvils (or anvils); die forging is to place the workpiece in a mold of a given size and shape, then apply pressure to the mold for forging deformation, and obtain the required forgings .
Effect of thermal deformation on the as-cast microstructure of aluminum:
The thermal deformation can most effectively change the as-cast microstructure of aluminum and aluminum alloys, and the appropriate amount of deformation can cause the following favorable changes in the as-cast microstructure.
(1) General thermal deformation is accomplished by repeated deformations in multiple passes. Since the hardening and softening processes occur simultaneously in each pass. The deformation breaks up the coarse columnar grains, and through repeated deformation, the structure of the material becomes a relatively uniform and small equiaxed grain. At the same time, some tiny cracks can be healed.
(2) Due to the hydrostatic pressure in the stress state, the bubble welding existing in the as-cast structure can be promoted, the shrinkage cavity is compacted, loosely compacted, and becomes a denser structure.
(3) Due to the enhanced thermal mobility of high-temperature atoms, the non-uniformity of the chemical composition of the ingot is relatively reduced by the free diffusion and heterodiffusion of atoms under the action of compressive stress.
The effect of cold deformation on the internal structure and properties of aluminum:
(1) Change in grain shape
As the shape changes, the grains are elongated, drawn or flattened along the direction of the maximum principal deformation. The greater the degree of cold deformation, the larger the grain shape changes.
After the metal crystal has undergone sufficient cold plastic deformation, many orientations appear in the grain, and the size is about 10-3 to -10-6 cm. It seems that the metal is deformed and then pulverized into many small pieces, but these small pieces ( Or between small grains, the orientation difference is not large (less than 10), so they are still maintained in the same large grain range. These small crystal blocks are called subcrystals. This kind of structure is called substructure (or mosaic). organization). The size, completeness, and orientation difference of the subcrystal are related to the purity, deformation and deformation temperature of the material. When the material contains impurities and the second phase, the subgrain formed is small in the case of large deformation and low deformation temperature. The orientation difference between the subcrystals is large, and the integrity of the subcrystals is poor (that is, the distortion of the crystal lattice in the subcrystal is large). During the cold deformation process, the subgrain structure plays an important role in the work hardening of the metal. Due to the different orientation of each crystal block, the boundary is a large number of dislocation entanglements, which hinders the further slippage in the crystal. Therefore, the substructure can increase the strength of aluminum and aluminum alloy materials.
(3) Deformed texture
During the cold deformation process of aluminum and aluminum alloys, due to the external force, the interaction between the internal crystal grains and the development direction of the deformation, the crystal grains are rotated relative to the external force axis, and the slip of the action is The direction of the direction of the force axis (or the direction of the maximum main deformation) is directional. In the case of a large degree of cold deformation, the case where the grain position changes from a disordered state to an ordered state is called a preferred orientation. The fibrous structure thus formed has a strict orientation relationship and is called a deformed texture. The textured texture can be divided into a silk texture (such as a texture formed under wire drawing, extrusion, and swaging conditions) and a board texture (such as a rolled texture). When the material having the cold-deformed texture is annealed, since the grain orientation tends to be uniform, there are always some orientational ingots which are prone to nucleation and growth. Annealed structures with texture are often formed, and such structures are referred to as recrystallized textures. The texture of the yarn can be obtained by stretching, drawing and round bar extrusion, and the board texture can be obtained by wide-plate rolling, strip rolling and flat belt stretching. The texture gives the material a significant anisotropy and in many cases texture hardening occurs. In actual production, it is necessary to control the deformation conditions, make full use of its advantageous aspects, and avoid its disadvantageous aspects.
(4) Intragranular and intergranular damage
In the cold deformation, the healing process of the softening process does not occur, due to the complex effects of slip (movement of dislocations and its hindrance, double slip, cross slip, etc.), twin crystals, and the relative movement of the grains. The rotation causes some micro-cracks, voids and other defects in the interior of the grain and the grain boundary to reduce the density of the aluminum, which is the source of microcracks and macroscopic breakage.