Research On Hot Spinning Process And Microstructure Evolution Of AZ81

Modern spinning technology is an advanced plastic forming process,which is widely used in aviation, aerospace, military and other metal precision processing technology. With wide application of spinning in aluminum alloy wheels, research on the magnesium alloy spinning wheels gradually is put on the agenda. For this,we carry out the spinning test using the AZ81 magnesium cast alloy with good performance and excellent overall mechanical properties in this paper, and study the deformation behavior of the powerful spinning Of cast magnesium alloy, which is prepared for the foundation of the spinning technology of magnesium wheels, and lay the basis for the microstructure and performance. This paper mainly studies AZ81 magnesium alloy from cast,homogenization to every spinning state and so on a series of microstructure evolution and the spinning crack behavior of the inner surface.The research results are drawn as follows:①There is a lot of dendrite segregation in the AZ81 casting magnesium alloy, which easily results in microcrack in follow-up hot deformation and finally reduce the plastic deformation ability. In order to improve the subsequent thermal processing performance, the impact of the homogenization process on its microstructure and performance is studied, which accepts the best homogenization parameters of AZ81 magnesium alloy and it's 400℃/8h.②The finite element simulation analysis shows that the deformation along the thickness direction in the spinning process is uneven. There is a deformed sequence that the deformation is first produced in the spinning work piece outside and then gradually extended effects to its internal; the level of deformation is also different from each other that the maximum near the roller region, and followed by decreasing inward.③The impact of some key parameters of spinning (spinning pass, thinning rate, spinning temperature) on the microstructure of the AZ81 magnesium alloy in the spinning deformation is explored. The results show that the degree of grain refining has a certain critical value in multi-pass spinning deformation, the grain size will not be changed by deformation increase; In addition to an increase of spinning pass and the thinning rate in a certain range, lower the temperature during deformation is also beneficial to the grain refinement, however, the higher spinning temperature will promote the trend that the refinement grain has grown up late in the deformation, at the same time, re-heating between passes will make the recrystallization microstructure recover and soften, which results in the grain growth.④The characteristics of spinning microstructure during AZ81 magnesium alloy hot deformation is explored. the phenomenon of grain refinement obviously occurs in the AZ81 magnesium alloy cast microstructure, including two refined ways of " fragmentation of polycrystalline deformation " and "dynamic re-crystallization". In small deformation, primarily regard " fragmentation of polycrystalline deformation " as the main,and accompanied by dynamic recrystallization in Local area of deformation; With the increase of deformation, "Dynamic recrystallization" gradually dominate, which promotes the strengthen of the grain refinement. Besides, there is "flow line" in hot spinning microstructure.⑤After research on the cracking behavior of the AZ81 magnesium alloy in hot spinning process, it is founded that the ring crack of inner surface is the main manifestations of the spin splitting, its crack mainly based on the intergranular crack. In the spinning process, The accurate control of the thinning rate and deformation temperature is to ensure that the ring cracking does not appear in deformation.