Effects of calcium addition on as-cast microstructure and mechanical properties of Mg-5Zn-5Sn alloy

The effects of Ca addition on the as-cast microstructure and mechanical properties of the Mg-5Zn-5Sn (mass fraction,%) alloy were investigated.The results indicate that an addition of 0.5%-1.5% (mass fraction) Ca to the Mg-5Zn-5Sn alloy not only refines the as-cast microstructure of the alloy but also causes the formation of the primary and/or eutectic CaMgSn phases with high thermal stability;an increase in Ca amount from 0.5% to 1.5% (mass fraction) increases the amount and size of the CaMgSn phase.In addition,Ca addition to the Mg-5Zn-5Sn alloy improves not only the tensile properties at room temperature and 150 ℃ but also the creep properties.Among the Ca-containing Mg-5Zn-5Sn alloys,the one added 0.5% (mass fraction) Ca obtains the optimum ultimate tensile strength and elongation at room temperature and 150 ℃,however,the alloy added 1.5% (mass fraction) Ca exhibits the optimum yield strength and creep properties.     

Effects of little Ce addition on as-cast microstructure and creep properties of Mg-3Sn-2Ca magnesium alloy

The effects of little Ce addition on the as-cast microstructure and creep properties of Mg-3Sn-2Ca magnesium alloy were investigated. The results indicate that adding 0.5% (mass fraction) Ce to Mg-3Sn-2Ca alloy does not cause the formation of any new phase in the alloy. However, an interesting microstructural change in the as-cast Mg-3Sn-2Ca alloy added with 0.5%Ce is observed. After adding 0.5%Ce to Mg-3Sn-2Ca alloy, not only the volume fraction of CaMgSn phase in the alloy is decreased but also the CaMgSn phases in the alloy are refined. In addition, adding 0.5%Ce to Mg-3Sn-2Ca alloy can also improve the creep-resistant properties of the alloy. After adding 0.5%Ce to Mg-3Sn-2Ca alloy, the second creep rate of the alloy at 150 °C and 70 MPa for 100 h changes from 3.28×10⁻⁸ to 1.81×10⁻⁸ s⁻¹.     

Comparison of as-cast microstructure,tensile and creep properties for Mg-3Sn-1Ca and Mg-3Sn-2Ca magnesium alloys

The as-cast microstructure,tensile and creep properties of Mg-3Sn-1Ca and Mg-3Sn-2Ca magnesium alloys were investigated and compared by using optical microscopy and scanning electron microscopy,X-ray diffraction analysis and tensile tests. The results indicate that the as-cast microstructures of Mg-3Sn-1Ca and Mg-3Sn-2Ca alloys are different.The former is mainly composed ofα-Mg,eutectic CaMgSn and solid state precipitation of Mg 2 Sn,whereas the latter is mainly composed ofα-Mg, primary CaMgSn,eutectic CaMgSn and Mg2Ca phases.As a result,the two alloys obtain different tensile and creep properties. Mg-3Sn-1Ca alloy shows relatively higher ultimate tensile strength and elongation at room temperature and 150℃than Mg-3Sn-2Ca alloy,however,the yield strengths of Mg-3Sn-1Ca alloy at room temperature and 150℃are relatively low.In addition,the creep properties of Mg-3Sn-1Ca alloy at 150℃and 70 MPa for 100 h are obviously lower than those of the Mg-3Sn-2Ca alloy.     

Effect of element Gd on phase constituent and mechanical property of Mg-5Sn-1Ca alloy

The Mg-5Sn-1Ca-xGd (x=0, 1) alloys were chosen to investigate the change in solidification paths, phase formation and mechanical properties. The microstructure of as-cast Mg-5Sn-1Ca alloy is composed of α-Mg, Mg2Sn and CaMgSn phases. With the addition of Gd, the formation of the Mg2Sn phase is impeded and the CaMgSn phase is refined, whereas the ultimate tensile strength and elongation decrease. The possible reasons for the variation in microstructure and mechanical properties were discussed.     

Microstructure characterization and effect of extrusion temperature on biodegradation behavior of Mg-5Zn-1Y-xCa alloy

Microstructure and biodegradation behavior of as-cast and hot extruded Mg-5Zn-1Y alloy containing different amounts of calcium (0.0%, 0.1%, 0.5%, and 1.0%, mass fraction) were explored. The extrusion process was conducted at three different temperatures of 300, 330, and 370 °C. Chemical composition, phase constitution, microstructure, and biodegradation behavior of the alloys were investigated. The macro- and micro-scopic examination revealed that the addition of Ca refines the grain structure and forms an intermetallic phase, Ca₂Mg₆Zn₃. The hot extrusion process resulted in breaking the intermetallic phases into fine particles routed to the extrusion direction. Moreover, dynamic recrystallization happened in almost all alloys, and more bimodal microstructure was formed in the alloys when the alloys were extruded at 370 °C. Polarization curves showed no passive region, which indicated that active polarization dominated in the alloys; therefore, grain refining through Ca addition and dynamic recrystallization over hot extrusion operation increased biodegradation rate. The results show that the as-cast Mg-5Zn-1Y-0.1Ca alloy provides the highest corrosion resistance, and the extruded Mg-5Zn-1Y-0.5Ca alloy at 300 °C shows the lowest biodegradation rate among the extruded alloys. Therefore, hot extrusion does not always improve the biodegradation behavior of magnesium alloys.     

Electrochemical Hydrogen Storage Characteristics of the as-Cast and Annealed La0.8-xPrxMg0.2Ni3.35Al0.1Si0.05 (x=0~0.4) Electrode Alloys

研究了Mg-3.8Zn-2.2Ca-xSn(x=0,0.5,1,2,质量分数%)镁合金的铸态组织、抗拉性能和蠕变性能。结果发现:在含Sn合金中会形成CaMgSn相,并且随着Sn含量从0.46%增加到1.88%(质量分数),合金中CaMgSn相的数量增加。同时,合金中Ca2Mg6Zn3相的形貌从最初的连续和/或半连续网状转变为半连续和/或断续状。此外,含Sn合金的晶粒被明显细化,其中含0.90%Sn合金的晶粒最细。与三元合金相比,含0.46%和0.90%Sn合金的抗拉性能和蠕变性能改善明显,而含1.88%Sn合金的屈服强度和蠕变性能虽然得到改善,但其抗拉强度和延伸率减小。在含0.46%、0.90%和1.88%Sn的3个合金中,含0.90%Sn的合金显示了优化的抗拉性能和蠕变性能。     

稀土Y元素对铸态镁合金组织与力学性能的影响

采用熔炼工艺制备了Mg-2.0Zn-0.2Ca与Mg-2.0Zn-0.2Ca-2Y合金,研究了两种合金的铸态组织及力学性能。结果表明,Y元素的添加细化了Mg-2.0Zn-0.2C合金的铸态组织。Mg-2.0Zn-0.2Ca合金主要由α-Mg与少量Mg₇Zn₃相组成,添加2wt%的Y后,改变了Zn在Mg基体中的固溶度,降低了其固溶强化效果,同时组织中形成了I相和W相。添加Y元素后,合金的规定塑性延伸强度升高,从41.0 MPa升高到50.6 MPa;伸长率降低,从12.6%降低到4.0%。     

Microstructure and mechanical properties of as-extruded Mg-Sn-Zn-Ca alloy with different extrusion ratios

The effect of extrusion ratio on microstructure and mechanical properties of as-extruded Mg-6Sn-2Zn-1Ca (TZX621) (mass fraction, %) alloy was investigated. It is found that incomplete dynamic recrystallization (DRX) took place in as-extruded TZX621 alloy. As the extrusion ratio was increased from 6 to 16, both fraction of un-DRXed grains and average size of DRXed grains in as-extruded TZX621 alloy decreased and the basal texture was weakened. Coarse CaMgSn phase was broken into particles and fine Mg₂Sn phase precipitated from α-Mg matrix during hot extrusion. Yield strength, ultimate tensile strength and elongation of as-extruded TZX621 alloy with extrusion ratio of 16 reached 226.9 MPa, 295.6 MPa and 18.1%, which were improved by 36.0%, 17.7% and 13.5%, respectively, compared to those of as-extruded TZX621 alloy with extrusion ratio of 6.     

Effect of Cu addition on microstructure and properties of Mg-10Zn-5Al-0.1Sb high zinc magnesium alloy

To improve the strength,hardness and heat resistance of Mg-Zn based alloys,the effects of Cu addition on the as-cast microstructure and mechanical properties of Mg-10Zn-5Al-0.1Sb high zinc magnesium alloy were investigated by means of Brinell hardness measurement,scanning electron microscopy (SEM),energy dispersive spectroscopy (EDS),XRD and tensile tests at room and elevated temperatures.The results show that the microstructure of as-cast Mg-10Zn-5Al-0.1Sb alloy is composed of α-Mg,t-Mg32(Al,Zn)49,φ-Al2Mg5Zn2 and Mg3Sb2 phases.The morphologies of these phases in the Cu-containing alloys change from semi-continuous long strip to black herringbone as well as particle-like shapes with increasing Cu content.When the addition of Cu is over 1.0wt.%,the formation of a new thermally-stable Mg2Cu phase can be observed.The Brinell hardness,room temperature and elevated temperature strengths firstly increase and then decrease as the Cu content increases.Among the Cu-containing alloys,the alloy with the addition of 2.0wt.% Cu exhibits the optimum mechanical properties.Its hardness and strengths at room and elevated temperatures are 79.35 HB,190MPa and 160MPa,which are increased by 9.65%,21.1% and 14.3%,respectively compared with those of the Cu-free one.After T6 heat treatment,the strengths at room and elevated temperatures are improved by 20% and 10%,respectively compared with those of the as-cast alloy.This research results provide a new way for strengthening of magnesium alloys at room and elevated temperatures,and a method of producing thermally-stable Mg-10Zn-5Al based high zinc magnesium alloys.     

Influence of Ca on mierostructure and corrosion resistance of Mg-14Li alloy

In order to improve the corrosion resistance of magnesium lithium alloy, Mg-14Li alloy with different content of Ca (0, 3, 5, 10wt.%) was prepared with a induction melting furnace. Electrochemical test and corrosion test were carried out in NaCI solution with different Cl^- concentrations. The results indicate that the microstructure of the Mg-14Li alloy with Ca consists of dendritic β phase and eutectic structure (β+CaMg₂). With the increase of Ca addition from 0, to 3, 5, 10wt.%, the corrosion resistance of the Mg-14Li alloy initially increases first and then decreases, and that of alloy with 3% Ca is the best. Therefore, the corrosion resistance of Mg-14Li alloy in NaCI solution can be effectively improved by adding proper amount of Ca. In addition, the concentration of Cl^- was one of important factors affecting the corrosion resistance of the Mg-14Li alloy, and the influence of Ca was slighter than that of Cl^-.

     

Effect of ageing treatment on microstructures,mechanical properties and corrosion behavior of Mg-Zn-RE-Zr alloy micro-alloyed with Ca and Sr

Effects of ageing treatment on the microstructures, mechanical properties and corrosion behavior of the Mg-4.2Zn-1.7RE-0.8Zr-xCa-ySr [x=0, 0.2 (wt.%), y=0, 0.1, 0.2, 0.4 (wt.%)] alloys were investigated. Results showed that Ca or/and Sr additions promoted the precipitation hardening behavior of Mg-4.2Zn-1.7RE-0.8Zr alloy and shortened the time to reaching peak hardness from 13 h to 12 h. The maximum hardness of 77.1±0.6 HV for the peak-aged Mg-4.2Zn-1.7RE-0.8Zr-0.2Ca-0.2Sr alloy was obtained. The microstructures of peak-aged alloys mainly consist of α-Mg phase, Mg₅₁Zn₂₀ phase and ternary T-phase. The Zn-Zr phase is formed within the α-Mg matrix, and the Mg₂Ca phase is formed near T-phase due to the enrichment of Ca in front of the solid-liquid interface. Furthermore, fine short rod-shaped β′₁ phase is precipitated within the α-Mg matrix in the peak-aged condition. The peak-aged Mg-4.2Zn-1.7RE-0.8Zr-0.2Ca-0.2Sr alloy exhibits optimal mechanical properties with an ultimate tensile strength of 208 MPa, yield strength of 150 MPa and elongation of 3.5%, which is mainly attributed to precipitation strengthening. In addition, corrosion properties of experimental alloys in the 3.5wt.% NaCl solution were studied by the electrochemical tests, weight loss, hydrogen evolution measurement and corrosion morphology observation. The results suggest that peak-aged alloys show reduced corrosion rates compared with the as-cast alloys, and minor additions of Ca and/or Sr improve the corrosion resistance of the Mg-4.2Zn-1.7RE-0.8Zr alloy. The peak-aged Mg-4.2Zn-1.7RE-0.8Zr-0.2Ca-0.2Sr alloy possesses the best corrosion resistance, which is mainly due to the continuous and compact barrier wall constructed by the homogeneous and continuous second phases.

     

Zr含量对Mg-5Zn-2Al镁合金组织与性能的影响

采用光学显微镜及拉伸试验机等手段,研究了Zr含量对Mg-5Zn-2Al合金铸态和热处理后显微组织及力学性能的影响.结果表明,Zr的加入使Mg-5Zn-2Al镁合金的铸态和热处理后的晶粒得到明显的细化.在铸态及热处理条件下,合金的抗拉强度与伸长率均呈现先上升后下降的变化趋势.对于铸态合金而言,Zr含量为0.6%时,Mg-5Zn-2Al合金的晶粒最为细小,并且其抗拉强度与伸长率均达到最大值,为215 MPa和12.563%.经热处理后,合金的抗拉强度较铸态得到了显著地提高.当Zr含量为0.6%时,合金的抗拉强度达到最大,为249 MPa.     

Effect of La addition on semi-solid microstructure evolution of Mg-7Zn magnesium alloy

Semi-solid billets of Mg-7Zn and Mg-7Zn-0.3La alloys were prepared by semi-solid isothermal heat treatment. The effects of the La element on the as-cast and semi-solid microstructures of Mg-7Zn alloy were investigated. Meanwhile, the effects of isothermal temperature and holding time on the evolution of the semi-solid microstructure of Mg-7Zn-0.3La alloy were also studied. Results indicate that the addition of a small amount of La can significantly refine the as-cast and semi-solid microstructure. During the semi-solid thermal transformation, the size and shape factor of solid particles decrease at first and then increase with the increase of isothermal temperature and holding time. The semi-solid microstructure of Mg-7Zn-0.3La alloy obtained by holding at 605 °C for 30 min is the optimal. The average size of solid particles, shape factor, and solid fraction are 42 µm, 1.45 and 61.8%, respectively. At the same time, a comparative study on the coarsening process of particles in the semi-solid billets of Mg-7Zn and Mg-7Zn-0.3La alloys reveals that the addition of La effectively decreases the coarsening rate of solid particles and restricts the growth of solid particles.

     

Microstructure and Mechanical Properties of a Ag Micro-Alloyed Mg-5Sn Alloy

Effects of 1.5 wt.% Ag addition and solid solution?+?artificial ageing at 160 °C on the microstructure and mechanical properties of a Mg-5Sn alloy have been studied. The results show that Ag addition has significantly hardened the solution-treated Mg-5Sn alloy. During the ageing process, the hardness increase rate and the strength and ductility of the Mg-5Sn alloy at each state are also improved by Ag addition. The improved strengthening behavior is primarily attributed to the refinement distribution of the Mg₂Sn precipitates, the enhanced precipitation process, and the synergistic strengthening effect of Mg₂Sn and a metastable plate DO₁₉ phase formed at lower ageing temperature. For each solution-treated alloy, the strength and ductility are higher than the corresponding cast ones. Ageing further enhances the yield strength, and the ductility of the Mg-5Sn-1.5Ag alloy is also increased after ageing. The fracture surfaces of the both peak-aged alloys exhibit the characteristic of a mixture of quasi-cleavage and ductile fracture.     

Microstructure modification and precipitation strengthening for Mg–6Zn–1Mn–4Sn–0.5Ca through extrusion and aging treatment

The microstructure revolution and mechanical properties of as-extruded and peak-aged Mg–6Zn–1Mn– 4Sn–0.5Ca (ZMT614–0.5Ca) alloy were studied by OM, SEM, TEM, hardness testing and tensile testing. The results showed that the as-cast ZMT614–0.5Ca alloy mainly consisted of α-Mg, Mg–Zn and CaMgSn phase. The hot extrusion process effectively refined the microstructure and led to a completely dynamic recrystallized microstructure. The average grain size of as-extruded alloy was ˜4.85 μm. After solution treatment, remained CaMgSn with high melting point played a significant role in pinning effect and impeding the migration of grain boundary. After aging treatment, peak-aged ZMT614–0.5Ca alloy exhibited a good combination of strength and ductility, with yield strength, ultimate tensile strength and elongation being 338 MPa, 383 MPa and 7.5%, respectively. The yield strength of the alloy increased significantly by around 36% compared with that in as-extruded condition, which should be attributed to the precipitation strengthening of β' phase.     

Microstructure and corrosion behavior of Mg-Sn-Ca alloys after extrusion

Mg-Sn-Ca alloys promise a reasonable corrosion resistance in combination with good creep resistance, likely due to the presence of Ca2-xMgxSn and other phases. The selected alloys with 3% Sn and Ca in the range of 1%-2% have been extruded in order to achieve more homogeneous microstructure compared with the as-cast alloys. Optical microscopy(OM) and X-ray diffraction(XRD) techniques were used to study the microstructure and phases of these alloys. The corrosion behavior of these alloys was investigated by means of salt spray test and potentio-dynamic measurements. The results obtained on the alloys Mg-3Sn (T3), Mg-3Sn-1Ca (TX31), and Mg-3Sn-2Ca (TX32) indicate the presence of the same phases in as-cast and after extrusion, namely Mg2Sn, Ca2-xMgxSn, and Ca2-xMgxSn/Mg2Ca, respectively. However, due to the occurrence of extensive recrystallization in the extrusion process, the grain size has significantly reduced after extrusion. The reduction leads to the improvement of the corrosion resistance after extrusion which is then comparable with the commercial alloy AZ91D.     

Effects of Minor Zr and Sr on As-Cast Microstructure and Mechanical Properties of Mg-4Y-1.2Mn-1Zn (wt.%) Magnesium Alloy

The effects of minor Zr and Sr on the as-cast microstructure and mechanical properties of the Mg-4Y-1.2Mn-1Zn (wt.%) alloy were investigated using optical and electron microscopies, differential scanning calorimetry (DSC) analysis, and tensile and creep tests. The microstructural results indicate that small additions of Zr and/or Sr to the Mg-4Y-1.2Mn-1Zn alloy do not cause an obvious change in the morphology and distribution of the Mg₁₂YZn phase in the alloy. The tensile and creep tests indicate that, although small additions of Zr and/or Sr to the Mg-4Y-1.2Mn-1Zn alloy do not have obvious effects on the creep properties of the alloy, the tensile properties at room temperature and 300 °C for the alloys added with Zr and/or Sr are improved. Among the Zr- and/or Sr-containing alloys, the alloy specifically added with of 0.5 wt.% Zr + 0.1 wt.% Sr obtains the optimum tensile properties, and is followed by the alloys added with 0.5 wt.% Zr and 0.1 wt.% Sr.     

不同Zn/Cu质量比对Mg-Zn-Cu显微组织和性能的影响

论文采用光学显微镜、X射线衍射仪、扫描电子显微镜及显微硬度测试、室温和高温拉伸性能测试、蠕变性能测试研究了Ce和不同的Zn /Cu质量比对Mg-Zn-Cu显微组织和室温及高温力学性能的变化规律、高温变形性能、强化机制和抗蠕变性能的影响。研究结果表明,室温下挤压态Mg-8Zn-8Cu-Ce的拉伸强度和屈服强度分别为320 MPa和291 MPa,在423K温度下,拉伸强度仍高于220MPa。合金具有优良的蠕变性能,稳态蠕变速率为1.21×10_-8 s_-1,蠕变量仅为0.562%。在相同的变形温度下,铸造Mg-7Zn-3Cu-Ce的真实应力随着应变速率的增大而增大,表明合金是应变速率敏感材料。相同的应变速率下,合金的真实应力随着温度的升高而减小,但没有明显的动态再结晶和软化现象。     

Sb对Mg-5Sn-2Al-1.5Zn-0.8Si合金组织和性能的影响

在熔炼时以单质形式加入Sb元素,研究了不同含量的Sb对Mg-5Sn-2Al-1.5Zn-0.8Si合金显微组织和力学性能的影响。结果表明,Sb能与Mg基体结合生成Mg3Sb2相。加入0.9%(质量分数)的Sb对Mg2Si相的汉字状结构具有强烈变质作用,Mg2Si中的Si能与Sn发生取代作用,生成Mg2(Si,Sn)复合相,该相的物理性能介于Mg2Si与Mg2Sn之间。随着Sb含量的增加,铸态合金和挤压态合金的延伸率逐渐减小,而抗拉强度呈现先增加后降低的趋势。挤压态合金的强度和塑性明显优于铸态合金,并且Sb含量的增加有利于改善Mg-5Sn-2Al-1.5Zn-0.8Si合金的耐热性能。