Effect of temperature on the mechanical abnormity of the quasicrystal reinforced Mg-4%Li-6%Zn-1.2%Y alloy

The serrated phenomena of the quasicrystalline phase reinforced Mg-4%Li-6%Zn-1.2%Y alloy after the extrusion,solid solution treatment and aged treatment have been investigated at different temperatures.The result shows that when the temperature is above 100℃,the serrated phenomenon becomes weak and all the serrated amplitudes are lower than 1 MPa.Among them,the serrated amplitude of samples in aged condition is the lowest and the value is only 0.1-0.2 MPa.The underneath mechanism for the lower plastic instability at higher temperature(≥100℃)can be ascribed to the weak pining effect of solute atoms on the movement of dislocation and release of the pile-up dislocations.

Influence of the lithium content on the negative difference effect of Mg-Li alloys

The so-called 'negative difference effect'(NDE) was often defined by the increasing rate of hydrogen evolution from magnesium(Mg) surface under anodic polarization.In this work,a series of electrochemical tests and microstructure observations were performed to provide an evidence that the NDE of Mg-Li alloys can be retarded by increasing lithium content.Potentiostatic,galvanostatic and potentiodynamic polarization experiments using Mg-xLi(x=4,7.5 and 14 wt%) alloys electrodes indicated that Mg-4 Li alloy maintained the enhancing NDE prior to anodic dissolution as that of conventional Mg alloys.However,the emergence of β-Li phase weakened the NDE of duplex Mg-7.5 Li alloy at a low anodic current density,but it was still enhanced apparently after a high applied anodic value(more than 2 mA/cm^2).The surface observations,including the plane and cross-sectional morphologies,confirmed that the cracked surface film derived from the anodic dissolution resulted in the catalytic activity of NDE for Mg-4 Li and Mg-7.5 Li alloys.Furthermore,the NDE of Mg-14 Li alloy was suppressed obviously after a prior applied anodic polarization,which was attributed to the persistent and integrated surface film which endured a higher level of applied anodic potential and current.

Suppressing Effect of Heat Treatment on the Portevin–Le Chatelier Phenomenon of Mg–4%Li–6%Zn–1.2%Y Alloy

Microstructural evolution and Portevin-Le Chatelier（PLC） phenomenon of the as-extruded Mg-4%Li-6%Zn-1.2%Y alloy before and after heat treatment have been investigated.It has been demonstrated that for the as-extruded and solid solution treated（T4） samples,the PLC phenomenon could be obviously observed on tensile stress-strain curves.Moreover,the PLC phenomenon in T4 samples was more salient than that in the as-extruded condition,suggesting that the occurrence of PLC phenomenon was closely related to the super-saturation degree of solute atoms in the matrix.Since most of solute atoms were consumed for the formation of Mg Zn precipitates（β1′ and a little of β2′） during the subsequent ageing treatment（T6）,the PLC phenomenon of T6 samples was eliminated.Meanwhile,due to the pinning effect of the formed Mg Zn precipitates on mobile dislocations,the tensile strength of T6 samples was relatively higher than those of the other two conditions.

Effect of Icosahedral Phase on Crystallographic Texture and Mechanical Anisotropy of Mg–4%Li Based Alloys

Through investigating and comparing the microstructure and mechanical properties of the as-extruded Mg alloys Mg-4%Li and Mg-4%Li-6%Zn-l.2%Y （in wt%）, it demonstrates that although the formation of I-phase （Mg3Zn6Y, icosahedral structure） could weaken the crystallographic texture and improve the me- chanical strength, the mechanical anisotropy in terms of strength remains in Mg-4%Li-6%Zn-1.2%Y alloy. Failure analysis indicates that for the Mg-4%Li alloy, the fracture surfaces of the tensile samples tested along transverse direction （TD） contain a large number of plastic dimples, whereas the fracture surface exhibits quasi-cleavage characteristic when tensile samples were tested along extrusion direction （ED）. For the Mg-4%Li-6%Zn-I.2%Y alloy, typical ductile fracture surfaces can be observed in both ＂TD＂ and ＂ED＂ samples. Moreover, due to the zonal distribution of broken l-phase particles, the fracture surface of ＂TD＂ samples is characterized by the typical ＂woody fracture＂.

Reduction effect of final-pass heavy reduction rolling on the texture development,tensile property and stretch formability of ZWK100 alloy plates

Obviously planar anisotropy due to‘TD split’orthotropic texture(TD indicates Transverse direction)always exist in the Rare-earth(RE)or Ca containing Mg alloy sheets,which is likely caused by the lowreduction rolling(and annealing)as revealed in our previous research.In this work,the as-cast billets of a ZWK100 alloy were subjected to final-pass heavy reduction rolling(FHRR)at 500°C with different reductions(30%-70%)after rough rolling,aiming to investigate the reduction effect on the microstructure and texture formation.The results show that FHRR with higher reductions above 50%is in favor of shear banding formation but has little effect on the as-deformed texture components,and the excellent formability with single-pass reduction up to 70%is mainly ascribed to the activation of prismatic slip.FHRR with reduction above 50%and annealing can generate uniform grain structures of~10μm and symmetrical‘oblique-line split’texture in(0001)pole figures,with basal poles tilting by about 50°from ND(Normal direction)towards some oblique-line of TD and RD(Rolling direction)as well as uniform distribution of counter lines as an annular shape,resulting in excellent elongation to failure of~50%and ultra-low planar anisotropyΔr_of~0.1 and high stretch formability(Erichsen value:8.1).The formation‘oblique-line split’texture in(0001)pole figures is mainly correlated with the preferred growth tendency of grains with■//RD,which was suggested to relate to the high mobility of some special boundaries such as 40°-45°■.The influences of starting textures on the mechanical properties,planar anisotropy and related deformation modes,as well as their correlations with the stretch formability were comparatively investigated with the‘TD split’orthotropic texture as a counterpoint.