| As a kind of ideal material, Magnesium alloy is used widely, and it is a new generation of high performance structural material, having the characteristics of light weight, high specific strength, good vibration damping, good thermal fatigue performance, not easy ageing, and having good thermal conductivity, and electromagnetic shielding ability, good performance of the die casting technology,especially the advantages of recycle easily. But because the mechanical processing performance and high temperature creep performance is poorer, limits its application scope. It is well known that rare earth elements are the widespread used alloying elements, having very good strengthening effect for room and high temperature mechanical properties. Heavy rare earth magnesium alloys with outstanding machining aggrandizement properties and heat resistance, such as Mg-Gd and WE magnesium, attract widespread attention, but the high cost is the main factor why the two types are failed to achieve wide application. At present, in areas such as automotive, aerospace, military industry, the state has the strong industrialization demand with the low cost of heat resistant magnesium alloy serving in 150℃-200℃and replacing ZM6 alloy. New low-cost heat-resistant magnesium alloy become a hot spot gradually. In this paper, it is to explore the microstructure and mechanical properties of rare-earth magnesium alloys by adding rare earth element Sm, and by changing the content of zinc element.In the research work, first of all, we smelt Mg-x Zn-4Sm-0.5Zr(x = 0,1.0 wt.%,2.0 wt.%, 3.0 wt.%, 4.0 wt.%) alloy by the gravity casting, studied the effect of content of zinc element on the microstructure and the comprehensive mechanical properties of as-cast and solid solution alloy structure; Then, manufacturing extrusion magnesium alloy by using the hot extrusion equipment, and adopting a variety of testing methods to describe the influence of zinc element on microstructure and mechanical properties of Mg-x Zn-4Sm-0.5Zr alloy, discussing magnesium alloy grainsize, texture changes’ impact on the mechanical properties of the deformation magnesium alloys.Experiments show that the average grain size of the as-cast Mg-4Sm-0.5Zr alloys is around of 35 um, and have a small amount of second phase of eutectic material Mg41Sm5 and some of the slag near grain boundary, but the grain boundary is thin, not the existence of the bulky second phase. With the addition of zinc element, the grain size have no obvious change, but the grain boundary have many thick second phase(Mg,Zn)3Sm, and the number increased gradually along with the increase of the content of zinc, combined with other literature shows that the effect of zinc element to prevent the grain to grew up in solid solution processing is not obvious than Zr element, namely, Zr element can significantly refine grain size.As-extruded Mg-x Zn-4Sm-0.5Zr alloys were composed of fine equiaxial grain structures(< 5μm) and coarse non-recrystallization grains distributed along extrusion direction. The intracrystalline phases were parallel to the extrusion direction.Extrusion deformation broke the second phase(Mg41Sm5) into tiny spherical granules,pinning near the grain boundary, hindering the sliding movement, and linear distribution along the ED direction. The massive(Mg,Zn)3Sm phases were also broken, forming the relatively large size globular grains randomly scattered within the crystal. There are negative correlation between mechanical strength change and average recrystallization grain size of as-extruded state alloy, and plastic changes relationship is contrasted, showing that by adding zinc element and completing extrusion process can realize the strength improved obviously. |
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