The tribological properties of combinative addition of nano-MoS2 and nano-SiO2 to the base oil have been investigated with a reciprocating ball-on-plate tribotester for magnesium alloy-steel contacts. The results demonstrate that the optimum mass ratio of nano-SiO2 to nano-MoS2 is 0.25：0.75. The optimum combinative addition into the base oil reduces the friction coefficient by 43.8% and the surface roughness （Sa） by 31.7% when compared to that found with the base oil. Meanwhile, the combinative addition of nano-MoS2 and nano-SiO〉 in comparison with single nanoparticles addition, is more pronounced in terms of the lubrication film stability. The excellent tribological properties of the SiO2/MoS2 combinations are attributed to the formation of physical adsorption films and tribochemical products during the rubbing process and the micro-cooperation of various nano- particles with different shapes and lubrication mechanisms.
The effects of Sn addition on the microstructure of as-cast and as-extruded Mg-9Li alloys were investigated. The results show that α-Mg, β-Li, Li2MgSn, and Mg2Sn are primary phases in the microstructures of the as-cast and as-extruded Mg-9Li-xSn （x=0, 5; in mass fraction, %） alloys. Li2MgSn phase evolves from continuously net-like structure in the as-cast state to fine granular in the as-extruded state. After the extrusion, Mg-9Li-5Sn alloy has finer microstructures. Li2MgSn or Mg2Sn compound can act as the heterogeneous nucleation sites for dynamic recrystallization during the extrusion due to the crystallography matching relationship Extrusion deformation leads to dynamic recrystallization, which results in the grain refinement and uniform distribution. The as-extruded Mg-9Li-5Sn alloy possesses the lowest grain size of 45.9 μm.
AZ31 Mg alloy sheets were processed by the conventional symmetrical extrusion(CSE)and the asymmetric extrusion(ASE).Progressive-asymmetric extrusion(PASE)and severe strain-asymmetric extrusion(SASE)were employed for ASE processes.The texture at near-surface and mid-layer zones of ASE sheets was diverse penetrating the normal direction(ND).This was attributed to an additional asymmetric shear strain deformation during the ASE process.(0002)basal planes of PASE sheets tilt to the shear deformation direction.Meanwhile,the basal texture intensity of PASE sheets has been weakened compared with one in CSE sheets.Grain refinement and tilted weak basal texture obtained by SASE process dramatically enhances the room temperature strength and plasticity of the extruded AZ31 magnesium alloy sheets.The microstructure and mechanical responses were examined and discussed.
Qingshan YangBin JiangHucheng PanBo SongZhongtao JiangJiahong DaiLifei WangFusheng Pan
The microstructural evolution and mechanical behavior of Mg-Mn-Ce magnesium alloy were investigated in the present study.Mg alloy was prepared with metal model casting method and subsequently hot extruded at 703 K with the reduction ratio of 101:1.The grains were dynamically recrystallized after the extrusion process.Moreover,the(0002)pole figure of Mg-Mn-Ce alloy developed a splitting of pronounced basal texture.The mechanical properties were different due to different angles between c-axis and loading direction(0°,45°and 90°)in the tensile tests.This significantly induces an asymmetry in the yield behavior.The Mg-Mn-Ce alloy exhibits a classical dimple structure as a result of slip accumulation and ductile tear.
Qingshan YangBin JiangXin LiHanwu DongWenjun LiuFusheng Pan
Mg-5Li-xSn （x=0.15, 0.25 and 0.65, mass fraction） alloys were prepared. The microstructures of these alloys were investigated through optical microscope （OM）, scanning electron microscope （SEM）, X-ray diffractometer （XRD） and energy dispersive spectrometer （EDS）. The results indicate that Sn additions produce a strong grain refinement effect on Mg-5Li alloy. The mean grain size of as-cast Mg-Li alloys with Sn is reduced remarkably from 556 μm to 345 μm, and that of the as-extruded alloys is reduced from 33 μm to 23 μm when the Sn content increases from 0.15% to 0.65%. The near net-like Mg2Sn phase in the as-cast alloys is verified at the grain boundaries. After extrusion, the granular Mg2Sn phase mainly exists inside the grains and thus can act as nucleation sites of α-Mg grains during the dynamic recrystallization and make the microstructure finer.
