Study On The Influence Of The Second Relative Twin Distribution In Magnesium Alloys

Magnesium alloy has high specific strength and specific stiffness and is easily recovered and the lightest metal structure material. Magnesium alloy which has wide application prospect is used in transportation, digital products, aerospace and other fields. Because magnesium alloy is hexagonal close-packed structure, the slip system is less in the low temperature. The plastic deformation ability of magnesium alloy is poor, so the application of magnesium alloy is severely restricted. Twin is one of the important deformation ways of magnesium alloy, and the second phase influences the distribution characteristics of twin. So it can be researched by controlling type, size and distribution of second phase on magnesium alloy. There is important application value to improve and enhance the organization and properties of magnesium alloy.This experiment prepares pure magnesium and ingot casting of magnesium alloy through directional solidification device and casting. Metallographic microscope, mechanical properties test, SEM and statistical analysis are used to study the second phase of pure magnesium and the organization of magnesium alloy. The twin was studied in different composition and content of magnesium alloy. Results are as follows.The different cooling rates are studied during the process of directional solidification to analysis the temperature gradient. At last, a large temperature gradient can be found. At the beginning of cooling, lower control box is closed. At the same time, the upper control box starts to cool in 20 ℃/10 min or 10 ℃/10 min. The latter can better improve the temperature gradient after analysis.The quantity and distribution of second phase are studied in pure magnesium. The particle size of second phase is 100μm below. There is more than 100μm in a few locations. The quantity of second phase increases gradually from the top down in the ingot casting. More second phase of big particle reduce the tensile performance of pure magnesium. However, the compression performance of pure magnesium has no evident changes. Pure magnesium appears twin crystal after tensile deformation.Magnesium alloy of directional solidification has composition segregation. The segregation phenomenon is more obvious when the composition of alloy is increased. There is second phase obviously in magnesium alloy of casting. The second phase increases when the composition of alloy is increased. Because the protection and the melting process are imperfect, more kinds of impurity elements in alloy will have an adverse effect on the performance of alloy.There is twin crystal in organization obviously after compression deformation. Twin crystals are parallel and cross. The most cross twin crystal are almost vertical. The grain orientation of cross twin crystal is{1012}.The length and thickness of twin crystal is uneven. Some twin crystal are started within the grain and ended in grain boundary, others are throughout the grain.