Effects Of Al、Zn、Sr On Microstrcture And Properties Of Mg-Sn Magnesium Alloy

So far, Magnesium alloy is the lightest metal structural materials in engineering applications, the research and application of magnesium alloy more and more concerns of the industry. Magnesium alloy has many drawbacks, especially magnesium alloy poor high temperature creep performance become an obstacle to further expand limit the application of magnesium alloy. Therefore, to improve the high temperature properties of magnesium alloy become a hot research materials at home and abroad. For the present,compared to the currently used of Mg-Al, Mg-Zn, etc. magnesium alloy, Mg-Sn alloys precipitated phase Mg2Sn having a higher melting point (771.5℃), is significantly higher than Mg17Al12(462℃), MgZn (347℃)phase. To Mg-Sn matrix, study elements Al, Zn, Sr changes in the microstructure and properties of magnesium alloy by alloying.By using as-cast forming technique and test facilities such as optical microscope, scanning electron microscope(SEM), X-ray diffraction (XRD), electronic universal testing machine, et cetera, studied the effects of Al、n addition on the microstructures and mechanical properties of the Mg-Sn alloys; Meanwhile, effects of Sr addition on the microstructures and mechanical properties of the Mg-7Sn-4Al-2Zn alloys have been investigated, and deeper studied the effects of Sn and Sr on the strengthening mechanism.The study shows that:(1) The test selected Mg-Sn system matrix alloy cast structure of the phase are a-Mg and Mg2Sn,ostructure was coarse equiaxed,Mg2Sn distribution within the grain and the grain boundary. Different content of Al in the Mg-Sn system (x=0,1,2,3,4,5), with the increase of Al content, microstructure gradually transformed by the coarse equiaxed dendrites and semi-continuous continuous and coarse mesh. Grain refinement,and grain boundary precipitation increasing, Mg17Al12and Mg2Sn the eutectic phase precipitation. With the Al content increases, the intragranular and grain boundaries in the solid solution of Al content is also increased accordingly. When the Al content from lwt.%increased to5wt.%, an ultimate tensile strength of Mg-Sn-Al based alloys showing the trend of increased Al content of5wt.%, the alloy tensile strength reaches maximum188MPa,At this time, the hardness reach up to59.0HB. But when the Al content is greater than3wt.%, the elongation at break of a downward trend.(2) Addition the different of content Zn (y=0,1,2,3,4,5) in Mg-Sn alloy, a small amount of Zn solid solution into the alloy. The matrix phase of Mg-Zn-Al cast alloys are α-Mg、Mg2Sn and MgZn phase.with the Zn content increases, coarse equiaxed grains were broken, gradually transformed into dendrites, and dendrites change with increasing Zn content thick, secondary dendrite dendrite arm spacing is significantly larger. When the Zn content of from1wt.% increased to5wt.%, the tensile strength of the limit of the Mg-Sn-Zn based alloys showing the trend of the first high, then low Zn content to3wt.%, the alloy tensile strength reaches the maximum187MPa, and when Zn content is5wt.%, the Brinell hardness of the alloy is54.3HB. When the Zn content exceeds lwt.%, the elongation is also gradually decreased.(3) Addation different content Sr on the Mg-7Sn-4Al-2Zn alloy, the organization of the alloy can be refined and generated a new SnMgSr strengthening phase. As the Sr content increases, the organization of the alloy by continuous or semi-continuous shape, the fine mesh-like gradually evolved into a dot or fluff, while the quantity and distribution patterns of of Mg2Sn phase and β-Mg17Al12phase has also been optimized. Add appropriate amount of Sr element of the test alloys at room temperature, the high temperature tensile properties are significantly improved, and reaches maximum when the Sr content is3wt.%, the room-temperature properties of the test alloys, tensile strength and yield strength were197MPa and165MPa, elongation is5.6wt.%. When the Sr content of2wt. alloy high-temperature tensile properties reach a maximum of173Mpa and129MPa. Elongation reaches a maximum8.6%. When the elements Sr are added to the amount of≤4wt.%, conducive to improve the tensile properties of the test. Constant high temperature mechanical properties of the alloy to improve the mainly due to microstructure refinement and high thermal stability SnMgSr.(4) When the Sr has been added, effectively improve the tensile fracture morphology of the test. Steps and rivers can be observed in the experiment, the tensile fracture cleavage plane mode, there are a small number of dimples. The tensile fracture characteristics of the experimental alloys cleavage and quasi-cleavage fracture. Strontium did not significantly alter the fracture mode of the alloy Mg-7Sn-4Al-2Zn. When Sr contain is3wt.%, a lot of cleavage-section fracture surface can be seen and which is relatively small. The high temperature tensile experimental alloys to intergranular fracture, Sr addition to the alloy cracks seem easy to extend along the thick SrMgSn particles and α-Mg matrix at the interface.