Research Of The Microstructure And Mechanical Properties Of Mg-Sn Based Magnesium Alloys

With the increase of the application of magnesium alloy, especially for the demand of the transportation, aerospace and 3C products, it is urgently need to develop new magnesium alloy.The Mg-Sn is a typical precipitation hardening system magnesium alloy, but it has some disadvantages like the Sn element segregation, the coarsening Mg2 Sn phase and the long age hardening time. Thus, a lot of research works of Mg-Sn alloy needs to continue in depth. In this paper, the Mg-Sn-Zn-Al series alloys were prepared in an induction furnace under Ar atmosphere. The microstructure and mechanical properties of Mg-3Sn-x Zn-1Al, Mg-x Sn-2Zn-1Al and Mg-5Sn-2Zn-1Al-0.1Ba alloys were investigated by X-ray fluorescence spectrometer(XRF), optical microscopy(OM), X-ray diffractometer(XRD), scanning electron microscopy(SEM) equipped with an INCA Energy 350 energy dispersive X-ray spectrometer(EDS), transmission electron(TEM), Webster microhardness tester and tensile tester, making clear the composition, structure and organization evolution of precipitated phases, establishing a preparation technology prototype of Mg-Sn alloy with high strength and high tenacity.The microstructure and mechanical properties of Mg-3.0Sn-x Zn-1.0Al alloy were investigated. 0.5-2.0 wt.% Zn refined the grains of the Mg-3.0Sn-1.0Al alloy, the amount of Mg2 Sn phase gradually increasing and the morphology of Mg2 Sn phase gradually coarsening with the Zn content increased. The solubility of Sn in α-Mg varies with the Zn content, the high content Sn in liquid phase would hinder the diffusion of Mg atoms and the growth of grains, which favors the formation of finer grains. With the increase of the Zn content, the grain size of as-extruded alloy significantly refined, the mechanical properties has improved significantly, and showed a certain degree of increase plastic at same time. Especially, the work hardening ability(1/YR) improved slightly with the increase of the Zn content, which means that the Zn can improve the strength of the alloy and plastic deformation ability, which can be attributed to the grain refinement effect and the uniform distribution of the second phase dispersion. In addition, the added Zn can improve the driving force for the precipitation and increase the number of fine Mg2 Sn precipitates. The increased Mg2 Sn precipitates improved the strength of the alloy, but reduced the plasticity.The microstructure and mechanical properties of Mg-x Sn-2.0Zn-1.0Al alloy were investigated. With increasing Sn content, the Mg2 Sn phase gradually changed from granular in the grains to reticular at the boundaries; and the branches of the crystal shape more obvious, namely the Sn element has obvious segregation. However, the number and size of Mg2 Sn are dramatically increased when the Sn content increased to 7%. After hot extrusion, dynamic recrystallization have occurred, recrystallization grain size is relatively uniform.The precipitated Mg2 Sn phases increased with the Sn content during the extrusion process, which are better for the mechanical properties. After aging for 60 h, the microhardness of alloy gradually tends to a stable value and the precipitated phase has reached the saturation state. With the increase of Sn content, the peak of the aging time has no obvious change, basically in the 60 h, but the peak hardness increased from 74.5 to 78.9Hv. The as-aged alloy has good strength and elongation, which is ascribed to the grain refinement and the Mg2 Sn particles. The as-rolled Mg-Sn-Zn-Al alloys have a fine grain size, low texture and twins. After annealing 1h under 300°C, the recrystallization occurs fully and twin disappear. After rolled, although the plasticity declined due to the twins, but the alloy still shows good mechanical properties, such as the tensile strength, yield strength and elongation of Mg-10Sn-2Zn-1Al alloy are 369 Mpa, 263 Mpa and 8.4%, respectively. After annealing at 250°C, 300°C, the strength of the alloy dropped sharply, especially for the yield strength, but the plastic has greatly improved.The microstructure and mechanical properties of Mg-5.0Sn-2.0Zn-1.0Al-0.1Ba alloy were investigated. The trace Ba has refined the dendrite of the alloy significantly, and formed Sn3Ba5, Sn Ba2 phases. The recrystallization may have occurred during hot extrusion process, the structure became homogeneous, and the mechanical properties of alloy have certain improvement. Microalloyed Ba make the peak age hardening time of Mg-Sn-Zn-Al alloy from 60 h reduced to 20 h, which promoted the precipitated phase nucleation and accelerated the precipitated phase during the artificial process. After T5 treatment, the mechanical properties increased, especially for the yield strength.