[China Aluminum Industry Network] As a new type of building structural material, aluminum pressure plate has unique advantages such as light weight, high specific strength, corrosion resistance, safety and fire prevention, convenient transportation and construction, long service life, and high recovery value. There is a wide range of applications in the engineering field. The thickness of the aluminum profile plate is mostly about U1mm. With the ever-increasing demand for pressboards, higher requirements have been placed on appearance, size and performance. In some load-bearing structures, thick gauge press plates are required to meet engineering requirements. At present, there are roll bending and stamping molding methods for the forming of press plates, and the roller bending molding process takes the leading position.

Aluminium profile plate roll forming is a process in which a plate is continuously bent by a longitudinal continuous roll forming machine under a cold state. The molding feature is that the thickness of the strip before and after the deformation is not changed; the length of the neutral line of each part after forming is equal to the width of the original plate; during the forming process, the bent part is in the elastic deformation, and it is also accompanied by plastic deformation and work hardening. There are two main types of roll bending forming process: 1) Sequential forming method: Firstly, the middle corrugation is gradually formed like an edge corrugation, or the corrugation is first formed from the edge corrugation and then the middle corrugation. The feature is that the blank width is simple to calculate, the installation and debugging of the roller is convenient, and the force required for molding is relatively small. However, the number of racks is relatively more demanding. 2) Simultaneously forming method: The corrugation on the section is formed at the same time. Its feature is that it can obtain finished products with less forming passes, but it needs to accurately calculate the width of the blank, and requires high installation precision for the forming unit; Due to the occurrence of metal hardening at the bend, the force required for molding is large, the forming roll wears more severely, and the increase in the thickness of the press platen brings difficulties to the molding equipment and process, such as: the force required for molding is greatly increased, and bending occurs During the forming process, the lateral displacement of the plate is large, and the bending radius of the upper and lower forming roller needs more consideration to match the bending performance of the material. If the molding process is not reasonable, it is easy to produce various defects. Therefore, the production of thick-gauge aluminum pressure plate imposes higher requirements on the equipment capacity of the tandem rolling mill, and the roll bending production process needs to be reasonably designed. The design of the hole bending radius needs to fully consider the deformation characteristics of the plate and the plate forming ability to reduce the occurrence of defects such as corner cracking.

This paper studies the roll forming process of thick gauge (3- 4mm) aluminum profile plate. Based on the aluminum alloy plate forming ability and the specifications of the profiled plate, the thick rolling aluminum profile plate sequential roll forming process is developed. Fracture SEM was used to microscopically characterize the small amount of cracks in the corners of the aluminum profiled plates. The causes of the fractures were analyzed. From the perspective of material selection and pretreatment, corresponding measures for reducing defects were proposed.

1 pressure plate composition, specifications and performance of aluminum alloy sheet used in this article is a relatively high strength rust-proof aluminum alloy, mainly used in shipbuilding industry, analysis of components can be found: aluminum - magnesium alloy contains a small amount of Mn, Cr and The addition of Ti element and Mn element enables the magnesium-containing phase such as Mg5Al8 to be dispersed and precipitated, and can play a role of dispersion strengthening, and at the same time, it can improve the corrosion resistance of the aluminum alloy. The added Cr and Ti elements can refine the alloy grains, while Fe, Si, Cu, etc. are impurity elements, and their presence has a greater negative impact on the properties and quality of the aluminum alloy.

2 Press Profile Forming Process It is generally believed that the sequential forming process requires the use of more forming rolls, but due to the reduction of the load, the actual sequential forming process can reduce the weight of the forming roll by about 20% compared to the simultaneous forming process. At the same time, during the forming process, the sheet begins to deform along the entire section, and the interaction between the bends makes it difficult to move the metal laterally. Especially when the forming roller is slightly misaligned, it causes the sheet to be taken during the forming process. The preset state is deformed, resulting in errors in shape and size. At the same time, there is a large stress in the forming process, in addition to easily causing the size of the edge of the profiled plate to be too large to form wrinkles and shape changes, and lateral bending and unevenness of the plate may also occur. In the sequential forming process, when a wave is formed, the free surrounding sheets are prone to the required lateral flow of the metal. The friction between the bending plate and the forming roller is reduced, which facilitates the forming of the sheet. Each of the two molding methods has its own advantages and disadvantages, but the sequential molding method has certain advantages for the medium and low-waveform press plates and some special-shaped press plates.

The raw material width of the press plate is 900~1200mm, and there are 4 trapezoidal slots in the press plate. During the forming process of the press plate, the plate is stretched in the rolling wheel and the groove type is deep. If a 3 mm aluminum alloy plate is used, the ratio of depth to thickness is 17:1, and the work hardening occurs locally during the deformation process. Plate forming performance requirements are high. In the forming process of the press plate, the metal plate is stretched in the transverse direction. Thus forming a trough. Groove depth requires that the lateral flow of the sheet during forming is relatively large, and simultaneous molding is used. The force acting on the sheet between the groove types makes the material flow more difficult, and it is likely to cause partial thinning or even fracture of the sheet. Because of the relative thickness of the plate, the simultaneous rolling of the four slots requires a greater rolling force for the equipment of the I-series. Based on the above analysis, according to the characteristics of simultaneous molding and sequential molding, the two schemes were compared, and a multi-point-by-pass sequential molding process was proposed. From Microsoft, the molding problem of high-hardening multi-groove aluminum alloy profiled plates was solved. The forming process of the aluminum profile plate is divided into two stages. First, the two intermediate grooves are molded, and then the two outer grooves are molded.

3 Crack defect analysis Fractures have a typical microporous polymerized fracture morphology characterized by the presence of a large number of dimples. The dimple is the result of micropore growth. The dimple contains most of the inclusions and the second phase. This indicates that the micropore grows on the interface of the inclusion or the second phase and the matrix. In addition, due to the strong work hardening ability of the substrate, the dimples are large and shallow. When the plate is bent, tensile stress is generated on the outside, micropores begin to appear, and then grows and polymerizes to form a central crack. This central crack extends along the direction perpendicular to the tension axis and ends up at the edge of the sample with about the sum axis. Cut off to a 45° plane.

Fe element is an impurity element in aluminum alloy. When the content is too large, metal compounds will be formed to form hard spots. The content ratio of one element and AL6 (FeMn) multiple hard and brittle phase will easily become the source of cracks during plastic processing, and it will have a significant effect. Work hardening properties of materials. Segregation of elements may easily lead to increased brittleness and decreased process performance. Simultaneously, magnesium elements segregate easily in the brittle and hard phases of particles formed of magnesium and aluminum, reducing the effect of precipitation strengthening, and resulting in increased brittleness. In the plastic processing process, cracking easily occurs. Crack source. In addition, a few crushed Si-rich hard spots and inclusions were also observed in the fractures, which were also easily broken during processing, resulting in crack initiation.

4 Conclusions 1) A thick gauge aluminum alloy profiler roll forming process was successfully developed. The pass reduction schedule and roll lateral movement allocation were given.

2) Fracture analysis of cracks in corners of a small number of profiled plates shows that there are some large particles in the interior of the aluminum alloy plate, which are easily broken during bending deformation, resulting in micro-cracking between the aluminum matrix interface and crack diffusion leading to corner cracking defects. The production.

3) Based on the above defect formation reasons, from the perspective of controlling microstructure and sheet formability, aluminum alloy sheet can be pre-annealed and heat treatment can be used to reduce the processing deformation rate and other measures to reduce the degree of work hardening, improve the sheet plasticity, thereby reducing cracks defect.

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