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6005A aluminum profile for metro
With the rapid development of modern transportation, the requirements for material properties are higher and higher. Because of its light weight, good corrosion resistance and high tensile properties, aluminum alloy products can realize the large-scale and wide body of their profiles. Therefore, the application of aluminum alloy in high-speed train body has become a research hotspot all over the world. 6005A aluminum alloy has the characteristics of medium strength, weldability and excellent corrosion resistance. 6005A aluminum profile for Metro is its excellent extrusion performance, which makes it widely recognized and applied as a large cross-section thin-wall hollow extrusion profile for vehicles. When aluminum alloy is extruded, many surface defects will appear on the products, such as hot crack, shrinkage tail, coarse crystal ring, etc., which will cause waste and defective products, so they need to be removed. Coarse crystal ring will affect the mechanical properties and surface quality of the parts, and seriously reduce the machinability of the alloy. Some aluminum alloy extruded products form coarse recrystallized grain structure area along the periphery of the product on the low magnification sample after solution treatment, which is called coarse grain ring. Due to the different shapes and processing methods of products, ring, arc and other forms of coarse crystal rings can be formed. The depth of the coarse-grained ring decreases gradually from the tail end to the front end, and even completely
6005A aluminum profile for metro
The formation mechanism of coarse-grained ring is that the coarse recrystallized grain structure area is formed by the sub crystalline area formed on the surface of the product by hot extrusion and heated solid solution treatment; If these coarse recrystallized grain structure areas appear on the extruded bar, they are generally called coarse grain rings, and if they appear on the extruded hollow profile, they are generally called cortical layers.
The main causes of coarse-grained ring are uneven extrusion deformation, too high heat treatment temperature and holding time, unreasonable chemical composition of alloy and so on. After inspection and analysis of 6005a-t6 profile sample, the following conclusions are drawn:
The yield strength and tensile strength of the samples with cortical defects are about 60% of those without cortical defects, and the elongation after fracture is 50% of those without cortical defects. It can be seen that the appearance of cortical layer seriously reduces the mechanical properties and should be controlled in the production process.
Coarse grain ring is also called coarse grain cortex. Although the defect does not destroy the continuity of the structure, the coarse grains appear clearly on the surface and cross section of the sample after corrosion. The depth of coarse-grained ring gradually decreases from tail end to head end and even disappears completely.
The fracture surface of the sample with cortical layer defects is small grains gathered together, the structure is not dense, there is no metal structure filling in some places, the fracture surface is non ductile layered serrated, and its plastic strength is very low. The fracture of the sample without cortical defects is fibrous, and the fracture mode is ductile fracture. The grain size mainly depends on the number of nuclei formed per unit time and the speed of grain growth. The coarser the grain, the thinner the dendrite network.
The cortical layer has a significant impact on the fatigue performance of profiles, which can significantly reduce the fatigue performance or make the fatigue performance unqualified.
Through the above analysis, we can take the following effective measures to avoid cortical defects and produce high-quality 6005A aluminum profile for metro:
Keep the inner wall of the extrusion cylinder clean and smooth to form a complete aluminum sleeve; Reduce the friction force during extrusion; The deformation shall be as uniform as possible (control temperature, speed, etc.); Avoid excessive quenching temperature; Multi hole die, back extrusion and static extrusion were used for extrusion; Organize production by quenching drawing aging method; Adjust the alloy composition and increase the recrystallization inhibiting elements; High temperature extrusion is adopted.
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