Directional Solidification Of Az91 Magnesium Alloy Technology And Organizational Research

Magnesium was discovered and isolated as a chemical element in 1808 by Sir Humphrey Davy. Magnesium is the lightest structural metal with a density of 1.74 g/cm?3. Pure Mg is rarely used for structural applications due to its poor mechanical properties. Therefore, Al and Zn have been introduced as major alloying elements for high-pressure die casting alloys. The main reason for using magnesium alloys is to lower the weigh load, predominantly in transportation industries. The weight reduction amounts to about 30% compared to Al alloys and to about 75% compared to steel. Magnesium as a hexagonal close-packed crystal structure (hcp). Here fore its deformation properties are poor.Magnesium alloys have wide applications in automobiles, aerospace and so on due to their low densities, high specific strength and stiffness, and their easy recyclability. Unfortunately, magnesium has a number of undesirable properties including poor corrosion resistance, inferior creep resistance and bad plastic processing ability that have hindered its widespread use in many applications. In recent years, great efforts have been devoted to solve the major problems mentioned above throughout the world.The unidirectional solidification technique 60 years of the 20th century developed a new casting technology, which refers to the use of coercive means of the solidification process, in the solidification of metals and the melt to establish temperature gradient along a specific direction, which is the melt nuclei in the type wall along with the heat flow in the opposite direction, the solidification direction is the crystallography preferred orientations. The formation of parallel columnar crystal, this texture has special mechanical properties. Even single-crystal materials have excellent thermal shock resistance, long fatigue life, high temperature creep resistance and medium temperature in the plastic. The unidirection solidification not only used manufacture the parts of aero-engine and IGT, But also widely used in preparation the persons with crystal, self-composite materials, magnetic materials, foam materials etc.This paper will be studied the unidirection solidification process and AZ91 magnesium alloy unidirection solidification texture. In the Investigation of the unidirection solidification process resolved in the process of technology issues, the implementation of supporting materials and equipment improvements, we prepared the directional solidification of magnesium alloy bar can be successfully used in the texture research. The research is using optical microscopy , field emission scanning electron microscopy , tensile testing and other analysis and testing methods, A systematic study is found the relationship solidification parameters, the temperature gradient GL and solid/liquid interface to move forward rate R, in directional solidification process. It has affected the texture growth pattern and texture structure.The results of the investigation show that, the directional solidification AZ91 magnesium alloy can conduct under non-vacuum conditions. Equipment advanced improved the temperature gradient in directional solidification process. Reduction of AZ91 magnesium alloy bar defects such as inclusions and porosity etc. Different temperature gradients and different Withdrawing speed have significant impact on AZ91 magnesium alloy growth patterns and texture forms. At a lower temperature gradient and smaller Withdrawing speed, an AZ91 magnesium alloy growth pattern is planar manner. With increases of the temperature gradient and the Withdrawing speed , flat growth pattern instability transform into cellular growth patterns; When the temperature gradient and Withdrawing speeds have reached a certain value, AZ91 magnesium alloy growth pattern changed from cellular growth patterns to dendrite growth; To further increase the temperature gradient and Withdrawing speed ,the dendrite growth pattern transformed into thin-cellular growth; When the temperature gradient is sufficiently high and the Withdrawing speed is large enough, the growth pattern will grow into a plane. Magnesium alloy texture is theα-phase (Mg17Al12) uniform dispersion in basic. distribution ofαphase transform into Tendency,Then coarse cellular - dendrite - thin-cellular , and finally texture into a mesh.The temperature gradient and withdrawing velocity has a significant impact on the morphology of magnesium alloy AZ91,By adjusting the different temperature gradient and withdrawing speed can artificially control the growth pattern AZ91 magnesium alloy and the solidification texture structure. Thereby improving the mechanical properties and high temperature performance of magnesium alloy, and it expand magnesium alloys in the engineering applications.