| As the lightest metal structural material, magnesium and magnesium alloys have been widely used in aerospace, traffic and electronics industriesbecause of their high specific strength, high specific stiffness, high thermal conductivity, good magnetic-shielding ability and excellent electromagnetic shielding. However, the application of magnesiumalloys is limited due to their poor mechanical properties(low strength and ductility) co MPared to that of thetraditional iron and steel materials. In order to overcome this limitation, two kinds of new magnesium alloys are fabricated in this paper. The one is the ZC63-xSn(x=0, 1, 2, 4) magnesium alloys subjected to different heat treatments, these alloys were fabricated by adding different amount Sn into the Mg-6Zn-3Cu magnesium alloy by the method of vacuum melting. The other is the AZ31 magnesium composite materials enchanced bySiC nano particles(SiCp) and different amount of graphene nanoplates(GNPs). The microstructures of all kinds of magnesium alloys were investigated bydifferential scanning calorimetry(DSC), optical microscopy(OP), scanning electron microscopy, X-ray diffraction(XRD), and energy dispersive X-ray spectroscopy(EDS). The mechanicla properties were investigated byvickershardness tester and electronic tensile test machine. The laws about the effects of the Mg(Zn,Cu) on the microstructuresand mechanical properties of ZC63 magnesium alloys and the GNPs on on the microstructuresand mechanical properties of AZ31 magnesium alloys aresummarized, which included the following four parts:The As-cast ZC63 magnesium alloy mainly consists of ?-Mg grains and Mg(Zn,Cu) particles(distributed at the grain boundaries of ?-Mg). Sn was dissolved in ?-Mg grains when Sn content was less than 2 wt.% while Mg2 Sn phase which were surrounded by Mg(Zn,Cu) formed when Sn content reached at 4 wt.%. Moreover, Sn addition refined both ?-Mg grains and Mg(Zn,Cu) particles, and increased the volume fraction of Mg(Zn,Cu) particles. The finest ?-Mg grains and Mg(Zn,Cu) particles and the largest amount of Mg(Zn,Cu) particles formed in ZC63-2Sn sample.CoMParing to Sn-free alloy, Sn-containing alloyshad greatly increased microhardness and the ZC63-4Sn sample achieved the highest value. Sn addition significantly improved the strength ofZC63 magnesium alloy due to grain refinementstrengthening, solid solution strengthening and precipitation strengthening. In particular, theultimate tensile strength(UTS) ofT6 samples increased from 194 to 259 MPa and theyield strength(YS)increased from 107 MPato 129 MPa by increasingthe Sn content from 0 wt.% to 2 wt.%.Both the?-Mg grains and the Mg(Zn,Cu) particles were refined in ZC63-xSn magnesium alloy subjected to extrude. In addition, TheMg(Zn,Cu) particles distributed throughout matrixinstead of at the grain boundaries, and Mg2 Sn particleswere apart from Mg(Zn,Cu) particles. The UTS and YS of the alloy subjected to extrude increased. What’s more, the microhardness and the elongationof thealloy subjected to extrude sharply increased.The microstructure of the SiCp/AZ31 magnesium composite materials were charactered by α-Mg, β-Mg17Al12 and SiCp and the microstructure of the GNPs/AZ31 magnesium composite materials were charactered by α-Mg, β-Mg17Al12 and GNPs. The α-Mg grains were refined due to the addition of GNPs or SiCp. And, the sample added t GNPs obtained the finest α-Mg. Moreover, the mechanical properties(microhardness and strength) of the GNPs/AZ31 magnesium composite materialswere higher than that of SiCp/AZ31 magnesium composite materials, due to the unique structure(finest grain and large aspect ratio) of GNPsGNPs addition refined the?-Mg grains of the GNPs/AZ31 magnesium composite materials, and the finest ?-Mg grains formed when the GNPs addition reached to 1.41 wt.%. Moreover, the increased of GNPs additionpromoted the solid solution of β-Mg17Al12. GNPs addition significantly improved the mechanical properties(microhardness and strength) of AZ31 magnesium alloy due to grain refinement strengthening, solid solution strengthening, precipitation strengthening, Orowan looping, strengthening induced by difference of coefficient of thermal expansion and load transfer. In particular, with the amount of the GNPs reached to 1.41 wt.%, the UTS value of theGNPs/AZ31 magnesium composite material reached to 198 MPa which wasextremely closed to that of the extruded AZ31 magnesium alloy used in this examination(204 MPa), the microhardness reached to 68.9 HV which was higher than that of the extruded AZ31 magnesium alloy used in this examination. |
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