Effects of Sn on microstructure of as-cast and as-extruded Mg-9Li alloys

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.

Effect of Li addition on mechanical properties and ageing precipitation behavior of extruded Al-3.0 Mg-0.5 Si alloy

The effect of Li(2.0 wt%)addition on mechanical properties and ageing precipitation behavior of Al-3.0 Mg 0.5 Si was investigated by tensile test,dynamic elasticity modulus test,scanning electron microscopy(SEM),transmission electron microscopy(TEM)and high-resolution transmission electron microscopy(HRTEM)images.The results show that the tensile strength of the Li-containing alloy can be significantly improved;however,the ductility is sharply decreased and the fracture mechanism changes from ductile fracture to intergranular fracture.The elasticity modulus of the Li-containing alloy increases by 11.6%compared with the base alloy.The microstructure observation shows that the Li addition can absolutely change the precipitation behavior of the base alloy,andδ′-Al_(3)Li phase becomes the main precipitates.Besides,β′′-Mg_(2)Si andδ′-Al_(3)Li dual phases precipitation can be visibly observed at 170℃ ageing for 100 h,although the quantity ofδ′-Al_(3)Li phase is more thanβ′′-Mg_(2)Si phase.The width of the precipitate-free zone(PFZ)of the Li-containing alloy is much wider at the over-ageing state than the base alloy,which has a negative impact on the ductile and results in the decrease of elongation.

Effect of addition of Al-Si eutectic alloy on microstructure and mechanical properties of Mg-12wt%Li alloy

Mg-12 Li, Mg-12 Li-3（Al-Si）, Mg-12 Li-7（Al-Si） and Mg-12 Li-9（Al-Si） alloys（all in wt%） were fabricated by high frequency vacuum induction melting in a water cooled copper crucible. After subsequently hotrolling and annealing, their microstructure and mechanical properties were investigated. Experimental results show that mechanical properties of Mg-12 Li alloy were significantly improved by the addition of Al-Si eutectic alloy. Mg-12 Li-7（Al-Si） alloy shows the highest strength of 196 MPa of the investigated alloys, which is about 1.8 times of the strength of Mg-12 Li alloy, and maintains high elongation of 27%.The improved mechanical property with addition of Al and Si in the eutectic proportion into Mg-12 Li alloy was attributed to the solution strengthening effect of A1 and precipitation hardening effect from AlLi and Mg_2 Si precipitates.

Influence of Al-Si additions on mechanical properties and corrosion resistance of Mg-8Li dual-phase alloys

Sheet samples of Mg-8Li,Mg-8Li-3Al,Mg-8Li-3AlSi and Mg-8Li-5AlSi alloys were obtained by hot rolling.Optical microscope,microhardness tester,nanoindentor,X-ray diffractometer and electrochemical analyzer were adopted to investigate the microstructures,micro-mechanical properties and corrosion resistance.Roller was preheated to 150°C before rolling process,and rolling reduction designed was about20% per pass with a total rolling reduction of 84%.The rolled plates were annealed at 200°C for 120 min.The tensile tests were performed at room temperature.Experimental results showed that both the strength and corrosion resistance of theα＋βdual-phase of Mg-Li alloy were significantly improved with adding Al-Si elements.The strength enhancement was attributed to the solid solution of Al into theα-Mg matrix and into theβ-Li matrix as well as to the precipitation strengthening of Mg2 Si particles.Besides,the dendrite grains ofα-Mg transformed to equiaxed ones with addition of Al into alloy Mg-Li.

镁-锂合金稀土转化工艺的研究

对镁-锂合金表面稀土转化成膜工艺进行了初步研究。分析了稀土盐硝酸镧转化、稀土盐硝酸镧+高锰酸钾转化工艺对稀土转化膜的形貌及耐蚀性能的影响。扫描电镜分析了稀土转化膜表面形貌;极化曲线、电化学阻抗谱测试技术研究了转化膜的耐蚀性能。结果表明:当在2g/L的硝酸镧转化液中加入2g/L的高锰酸钾时,镁-锂合金表面获得了均匀致密、裂纹细小的稀土转化膜;转化成膜时间对膜的耐蚀性也有不同程度的影响。