Magnesium silicon nitride (MgSiN2) was synthesized without any additives under a nitrogen gas flow (200 mL/min) using a nitriding method. The effects of temperature and holding time on its purity and morphology were i...Magnesium silicon nitride (MgSiN2) was synthesized without any additives under a nitrogen gas flow (200 mL/min) using a nitriding method. The effects of temperature and holding time on its purity and morphology were investigated. A single-phase MgSiN2 powder was obtained at 1350℃ for 1 h and 1250℃ for 11 h. However, the decomposition of MgSiN2 occurred at 1450℃, suggesting that the optimum temperature for the preparation of MgSiN2 from Mg-Si system was 1350℃. The phase purity, morphology, size of the product and elemental composition of the samples were detected by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy spectrometer (EDS), respectively. The evaporation of Mg and Si resulted in the formation of many voids in the blocky product. The temperature gradient promotes the growth of MgSiN2 on the surface of massive products along the tip. The concentration gradient of Mg and Si vapors in the void resulted in the columnar growth of MgSiN2.展开更多
The influences of silicon addition to commercially pure magnesium(CP Mg)and cooling rate during solidification on the as-cast microstructure and shear mechanical properties of Mg-Si alloys were systematically investig...The influences of silicon addition to commercially pure magnesium(CP Mg)and cooling rate during solidification on the as-cast microstructure and shear mechanical properties of Mg-Si alloys were systematically investigated.For this purpose,the Mg-0.6Si,Mg-1.34Si,and Mg-3Si(wt%)alloys were considered as hypoeutectic,eutectic,and hypereutectic alloys,respectively.By decreasing the geometrical modulus of the solidifying section(increasing cooling rate),remarkable grain refinement,refining the dendrite arm spacing(DAS),and modification of Mg_(2)Si particles were achieved.Moreover,the grain size was refined via Si addition in the hypoeutectic range,while coarsening of grain size at high Si concentrations was observed.The results of shear punch testing and hardness measurements demonstrated that the ultimate shear strength(USS)and hardness increased by increasing the cooling rate during solidification.Moreover,Si addition generally improved hardness,while the highest USS level was achieved for the eutectic alloy due to the fine grain size and strengthening effect of the eutectic constituent.However,regarding the hypereutectic Mg-3Si alloy that exhibited high hardness,the shear properties were inferior due to the detrimental effect of the primary Mg_(2)Si particles.Finally,the results were discussed with consideration of the relationship between strength and hardness,for which the critical effect of Si was clarified.展开更多
通过拉伸和埃里克森实验以及扫描电镜/能谱、透射电镜和金相分析,研究Mn的质量分数对Al Mg Si Cu铝合金汽车板显微组织、力学性能和成形性的影响·研究表明,随Mn质量分数增加,Al Mg Si Cu汽车板铝合金不可溶结晶相及弥散相粒子数量...通过拉伸和埃里克森实验以及扫描电镜/能谱、透射电镜和金相分析,研究Mn的质量分数对Al Mg Si Cu铝合金汽车板显微组织、力学性能和成形性的影响·研究表明,随Mn质量分数增加,Al Mg Si Cu汽车板铝合金不可溶结晶相及弥散相粒子数量均增加,不可溶结晶相使合金组织纤维化对板材冲压成形性不利,弥散相粒子阻碍再结晶晶粒长大;提高Mn的质量分数,Al Mg Si Cu汽车板铝合金的强度增加,但延伸率和冲压成形性降低·展开更多
The modification effect of neodymium （Nd） on Mg2Si in the hypereutectic Mg-3%Si （mass fraction） alloy was investigated by optical microcopy, scanning electron microscopy and X-ray diffraction. The results indicate...The modification effect of neodymium （Nd） on Mg2Si in the hypereutectic Mg-3%Si （mass fraction） alloy was investigated by optical microcopy, scanning electron microscopy and X-ray diffraction. The results indicate that the morphology of the primary Mg2Si transforms from coarse dendrite into fine polygon with increasing Nd content. The average size of the primary Mg2Si significantly decreases to about 10 ~ma with increasing Nd content up to 1.0%, and then becomes coarser again. The modification and refinement of the primary Mg2Si are mainly attributed to the poisoning effect. The NdMg2 phase in the primary Mg2Si transforms into NdSi and NdSi2 compounds as the Nd content exceeds 3.0%. Therefore, it is reasonable to conclude that the proper Nd （1.0%） addition can effectively modify and refine the primary Mg2Si.展开更多
The effect of Ca addition on modification of primary Mg_(2)Si,hardness and wear behavior in Mg-5 wt.%Si hypereutectic alloy has been investigated.The results showed clearly that without Ca addition,most of primary Mg_...The effect of Ca addition on modification of primary Mg_(2)Si,hardness and wear behavior in Mg-5 wt.%Si hypereutectic alloy has been investigated.The results showed clearly that without Ca addition,most of primary Mg_(2)Si appeared as coarse dendritic morphology with average size of about 215μm.With the addition of 0.1 wt.%Ca,the average size of primary Mg_(2)Si decreased to about 98μm,but their morphologies did not significantly changed.As the addition level of Ca increased to 0.3 wt.%,the average size of primary Mg_(2)Si decreased significantly to about 50μm and their morphologies changed to polyhedral shape.However,with further increasing Ca addition to 0.6 wt.%and 1 wt.%,some needle-like and blocky CaMgSi particles formed and the average size of primary Mg_(2)Si increased slightly,which could described as over-modification.The present work showed that the optimal modification effect could be obtained when the Ca content in the investigated alloy reached 0.3 wt.%.The modification mechanism may be referred mainly due to poisoning effect resulting from the segregation of Ca atoms at the growth front of the Mg_(2)Si and the adsorption effect of some Ca atoms in the Mg_(2)Si crystal growth plane.The 0.3 wt.%Ca-added alloy has the highest hardness value and the best wear resistance among all other alloys.An excessive Ca addition resulted in the formation of some needle-like and blocky CaMgSi particles,which was detrimental to hardness and wear behavior of the 0.6 wt.%and 1 wt.%Ca-added alloys.The wear mechanism of investigated alloys is a mild abrasive oxidative wear with little adhesion.展开更多
文摘Magnesium silicon nitride (MgSiN2) was synthesized without any additives under a nitrogen gas flow (200 mL/min) using a nitriding method. The effects of temperature and holding time on its purity and morphology were investigated. A single-phase MgSiN2 powder was obtained at 1350℃ for 1 h and 1250℃ for 11 h. However, the decomposition of MgSiN2 occurred at 1450℃, suggesting that the optimum temperature for the preparation of MgSiN2 from Mg-Si system was 1350℃. The phase purity, morphology, size of the product and elemental composition of the samples were detected by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy spectrometer (EDS), respectively. The evaporation of Mg and Si resulted in the formation of many voids in the blocky product. The temperature gradient promotes the growth of MgSiN2 on the surface of massive products along the tip. The concentration gradient of Mg and Si vapors in the void resulted in the columnar growth of MgSiN2.
文摘The influences of silicon addition to commercially pure magnesium(CP Mg)and cooling rate during solidification on the as-cast microstructure and shear mechanical properties of Mg-Si alloys were systematically investigated.For this purpose,the Mg-0.6Si,Mg-1.34Si,and Mg-3Si(wt%)alloys were considered as hypoeutectic,eutectic,and hypereutectic alloys,respectively.By decreasing the geometrical modulus of the solidifying section(increasing cooling rate),remarkable grain refinement,refining the dendrite arm spacing(DAS),and modification of Mg_(2)Si particles were achieved.Moreover,the grain size was refined via Si addition in the hypoeutectic range,while coarsening of grain size at high Si concentrations was observed.The results of shear punch testing and hardness measurements demonstrated that the ultimate shear strength(USS)and hardness increased by increasing the cooling rate during solidification.Moreover,Si addition generally improved hardness,while the highest USS level was achieved for the eutectic alloy due to the fine grain size and strengthening effect of the eutectic constituent.However,regarding the hypereutectic Mg-3Si alloy that exhibited high hardness,the shear properties were inferior due to the detrimental effect of the primary Mg_(2)Si particles.Finally,the results were discussed with consideration of the relationship between strength and hardness,for which the critical effect of Si was clarified.
文摘通过拉伸和埃里克森实验以及扫描电镜/能谱、透射电镜和金相分析,研究Mn的质量分数对Al Mg Si Cu铝合金汽车板显微组织、力学性能和成形性的影响·研究表明,随Mn质量分数增加,Al Mg Si Cu汽车板铝合金不可溶结晶相及弥散相粒子数量均增加,不可溶结晶相使合金组织纤维化对板材冲压成形性不利,弥散相粒子阻碍再结晶晶粒长大;提高Mn的质量分数,Al Mg Si Cu汽车板铝合金的强度增加,但延伸率和冲压成形性降低·
基金Project(A0420110401)supported by the National Security Basic Research,China
文摘The modification effect of neodymium （Nd） on Mg2Si in the hypereutectic Mg-3%Si （mass fraction） alloy was investigated by optical microcopy, scanning electron microscopy and X-ray diffraction. The results indicate that the morphology of the primary Mg2Si transforms from coarse dendrite into fine polygon with increasing Nd content. The average size of the primary Mg2Si significantly decreases to about 10 ~ma with increasing Nd content up to 1.0%, and then becomes coarser again. The modification and refinement of the primary Mg2Si are mainly attributed to the poisoning effect. The NdMg2 phase in the primary Mg2Si transforms into NdSi and NdSi2 compounds as the Nd content exceeds 3.0%. Therefore, it is reasonable to conclude that the proper Nd （1.0%） addition can effectively modify and refine the primary Mg2Si.
文摘The effect of Ca addition on modification of primary Mg_(2)Si,hardness and wear behavior in Mg-5 wt.%Si hypereutectic alloy has been investigated.The results showed clearly that without Ca addition,most of primary Mg_(2)Si appeared as coarse dendritic morphology with average size of about 215μm.With the addition of 0.1 wt.%Ca,the average size of primary Mg_(2)Si decreased to about 98μm,but their morphologies did not significantly changed.As the addition level of Ca increased to 0.3 wt.%,the average size of primary Mg_(2)Si decreased significantly to about 50μm and their morphologies changed to polyhedral shape.However,with further increasing Ca addition to 0.6 wt.%and 1 wt.%,some needle-like and blocky CaMgSi particles formed and the average size of primary Mg_(2)Si increased slightly,which could described as over-modification.The present work showed that the optimal modification effect could be obtained when the Ca content in the investigated alloy reached 0.3 wt.%.The modification mechanism may be referred mainly due to poisoning effect resulting from the segregation of Ca atoms at the growth front of the Mg_(2)Si and the adsorption effect of some Ca atoms in the Mg_(2)Si crystal growth plane.The 0.3 wt.%Ca-added alloy has the highest hardness value and the best wear resistance among all other alloys.An excessive Ca addition resulted in the formation of some needle-like and blocky CaMgSi particles,which was detrimental to hardness and wear behavior of the 0.6 wt.%and 1 wt.%Ca-added alloys.The wear mechanism of investigated alloys is a mild abrasive oxidative wear with little adhesion.
