The tribological properties of combinative addition of nano-MoS_2 and nano-SiO_2 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-SiO_2 to nano-MoS_2 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-MoS_2 and nano-SiO_2, in comparison with single nanoparticles addition, is more pronounced in terms of the lubrication film stability. The excellent tribological properties of the SiO_2/MoS_2 combinations are attributed to the formation of physical adsorption films and tribochemical products during the rubbing process and the micro-cooperation of various nanoparticles with different shapes and lubrication mechanisms.
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
