| As the lightest structural metallic materials, magnesium alloys have manyadvantages such as low density, high specific strength, high specific stiffness,excellent electro-magnetic shielding ability, good heat dispersion and processingproperties, and have been paid close attention by lots of researchers. Magnesium andmagnesium alloys have been extensively applied in automotive, communication andaircraft industries. However, its lower strength and poor corrosion resistance atelevated temperature, which is the main factor of limiting their wide application. Sowhat is an important study is to research and development new magnesium alloyswhich have high heat resistance and corrosion resistance in order to expand theirapplication.In this paper, the effects of rare earth Gd on the microstructures, room-temperature and elevated-temperature mechanical properties as also as corrosionresistance of Mg-Gd-Y-Sm-Zr magnesium alloy are studied through preparation ofalloy, analysis of microstructure by using optical microstructure, x-ray diffraction,scan electric microscopy and energy dispersive spectrometer, tensile properties testand static weight-loss test. The purpose of this research is to provide theoretical andpractical basis for further development and research on the Mg-Gd-Y-Sm-Zr alloy.The results show that, appropriate rare earth element Gd can effectively refinegrains of Mg-xGd-2Y-1Sm-0.5Zr(x=6,9,12) magnesium alloy, increase roomtemperature mechanical properties and elevated temperature mechanical properties,and remarkably improve corrosion resistance of alloy. For Mg-xGd-2Y-1Sm-0.5Zralloy with6%、9%and12%Gd, The microstructures of alloys have been improvedwhich is cast or solid solution and aging treatment. The microstructures are refined anduniform when the content of Gd is6%. At room temperature and elevated temperature,the tensile strength of alloy rise with the increase of Gd. When the content of Gd is 12%, the tensile strength of alloy reaches its maximum value at room temperature andelevated temperature, respectively,219.5MPa at room temperature,253.3MPa at200℃,282.6MPa at250℃,264.3MPa at300℃, but the elongation of alloy drop with theincrease of Gd. From room temperature to300℃, with the increase of temperature, theelongation of alloy rise, but the tensile strength rise at first and then drop, and reachthe maximum value at250℃, which is not consistent with general Mechanicalproperties-temperature change curve. Mg-xGd-2Y-1Sm-0.5Zr magnesium alloy haveabnormal mechanical behavior obviously.For Mg-xGd-2Y-1Sm-0.5Zr magnesium alloy with6%、9%and12%Gd, thecorrosion rates of the alloys increase firstly and then decrease with the increase of Gdcontent in0.5%、2.0%and3.5%NaCl solution for24h at25±3℃.With the additionof6%Gd, the corrosion rate of the alloy is the lowest and the corrosion resistance isthe best. The microcosmic morphologies of the corrosive surfaces of the alloys are inaccordance with the corrosion rates. With the increasing content of Gd, the corrosionseverity of the alloys are also enhanced firstly and then weakened with the increase ofGd content. With the addition of6%Gd, only a few small spots and the scratch can beseen, the corrosion resistance is the best. When the content of Gd is9%, the corrosionphenomenon becomes serious. Deep pits cover the whole surface, and the particle sizeof corrosion scale is bigger and even deep cracks appear in some areas. However,when the content of Gd reaches to12%, the alloy is corroded slightly, only a few spotsappear, and the particle of corrosion scale is smaller. The corrosion severity of thealloys are effected by the concentration of NaCl, the corrosion rates of the alloysincrease with the increase of the concentration of NaCl.It is considered that, Gd can effectively perfect the microstructures, improvetensile strength and corrosion resistance of Mg-xGd-2Y-1Sm-0.5Zr(x=6,9,12)magnesium alloy due to the synergistic effects of solid-solution strengthening,dispersion strengthening and fine-grained strengthening. |
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