Microstructure,tensile properties and compressive creep resistance of Mg-(5-8.5)%Sn-2%La alloys

The microstructure,tensile properties and compressive creep resistance of permanent-mould cast Mg-(5-8.5)%Sn-2%La (mass fraction) alloys were investigated.The results show that Mg-(5-8.5)%Sn-2%La alloys are all composed ofα-Mg phase, Mg_2Sn and Mg-La-Sn compounds.Compared with those of Mg-5%Sn binary alloy,the grain size and the content of Mg_2Sn compound in Mg-5%Sn-2%La alloy are decreased.With the increase of Sn content in Mg-(5-8.5)%Sn-2%La alloys,the content of Mg_2Sn compound increases,while that of...     

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。     

Investigation on the microstructure and mechanical properties of a cast Mg–6Zn–5Al–4RE alloy

Mg–6Zn–5Al–4RE (RE = Mischmetal, mass%) alloy was prepared by metal mould casting method. The microstructure and mechanical properties of the as-cast and heat-treated alloys were investigated. The results show that the phase compositions of the as-cast state alloy are supersaturated solid solution -Mg, lamellar β-Al₁₂Mg₁₇, polygonal Al₃RE and cluster Al₂REZn₂ phases. The mechanical properties, especially the ultimate tensile strength and elongation of the alloy were significantly improved by the heat treatment. Fracture surface of tensile specimens was analyzed by optical microscope and scanning electron microscope.     

Formation of 14H long period stacking ordered structure and profuse stacking faults in Mg–Zn–Gd alloys during isothermal aging at high temperature

This paper proposes a time–temperature-transformation diagram of an Mg–Zn–Gd alloy. An Mg₉₇Zn₁Gd₂ (at.%) alloy shows different precipitation sequences at low, medium and high temperatures. Low-temperature aging at <523 K brings about coherent β′-phase precipitation to a -Mg solid solution, resulting in increase in strength of the alloys. However, aging at medium and high temperatures >623 K led to strengthening of the Mg–Zn–Gd alloy, owing to the formation of profuse stacking faults and 14H long period stacking ordered structure from the supersaturated -Mg matrix, respectively.     

锡元素对925银性能影响的研究

采用含锡量0%~5%的首饰铸造用铜基补口合金制备6种925银,通过对比检测925银流动性、白度、显微硬度、拉伸强度,分析微观组织成分,对比观察抗硫化腐蚀能力。实验结果表明,铜基补口合金中锡元素含量在4%时925银合金拉伸强度最高,锡含量在1%~3%时拉伸强度呈线性增加;随着锡含量提高925银合金流动性提高,显微硬度增加,抗硫化变色性能提升,合金的白度和亮度降低,色差增大;通过微观组织观察,随着锡含量增加在相界面处形成二次析出高锡固溶体组织,影响合金拉伸强度,含锡固溶体组织白度及亮度低于Ag-Cu-Zn固溶体组织。     

Selection of promising quaternary candidates from Mg–Mn–(Sc, Gd, Y, Zr) for development of creep-resistant magnesium alloys

Recently developed Mg–Mn–Sc alloys show a considerable increase of creep resistance at elevated temperature. The endeavor to further improve the properties and to reduce cost of high-price Sc metal initiated a search for additional alloying elements. Gd, Y and Zr were considered for this purpose. The aim is to achieve a large quantity of suitable precipitations to improve mechanical properties using a minimum of expensive alloy element addition. The huge amount of possibilities of combining the elements Mg–Mn–(Sc, Gd, Y, Zr) and the time and cost effort of technological experiments require a preselecting of systems and alloy compositions. Thermodynamic phase diagram and phase amount calculations were performed to give hints for selecting promising candidates. A priority list of three quaternary systems is established: Mg–Mn–Gd–Sc, Mg–Mn–Sc–Y and Mg–Mn–Y–Zr, based on the classification of individual alloys. Most promising is MgMn1Gd5Sc0.8 (wt.%), but the alloys MgMn1Gd5Sc0.3 and MgMn1Y5Sc0.8 are also promising. The entire quaternary Mg–Mn–Y–Zr system is disqualified because of phase diagram features that are detrimental for the required microstructural engineering. The focused alloy development following this approach avoids a waste of time and effort.     

Microstructure and creep properties of Mg-4Al-2Sn-1 （Ca,Sr） alloys

The effects of Ca and Sr addition on the microstructure and creep properties of Mg-4Al-2Sn alloys were examined.Tensile tests at 25℃ and 200℃ and creep tests at 150℃ and 200℃ were carried out to estimate the room temperature and high temperature mechanical properties of these alloys.The microstructure of the Mg-4Al-2Sn alloy showed dendriticα-Mg,Mg17Al12 and Mg2Sn phases.The latter two phases precipitated along the grain boundaries.The addition of Ca and Sr resulted in the formation of ternary CaMgSn and SrMgSn phases within the grain.The grain size was reduced slightly with the addition of Sr and Ca.The tensile strength was decreased by the addition of Ca and Sr at room temperature.However,the high temperature tensile strength was increased.The creep strength was improved by the addition of Ca and Sr.     

Improved tensile properties of Mg-8Sn-1Zn alloy induced by minor Ti addition

In this study, the influence of minor titanium(Ti) addition on the microstructure and tensile properties of Mg-8Sn-1Zn based alloys were investigated by means of optical microscopy, X-ray diffraction, scanning electron microscopy, energy dispersive spectrometry, and tensile tests. The results showed that Ti can decrease the secondary dendrite arm spacing(SDAS). The tensile strength of the Mg-8Sn-1Zn-Ti alloys is initially increased by increasing the Ti content up to 0.09 wt.%, but subsequently decreased for further increase of Ti content. The improved tensile properties are attributed to the decreased SDAS and refi ned Mg_2Sn phases, as well as the increased fraction of tin(Sn) segregated regions. The tensile fracture surface of the studied alloys shows mixed characteristics of cleavage and quasi-cleavage fracture. Adding Ti does not significantly change the fracture mode of the studied alloys.     

Microstructures and properties of Mg–7Gd alloy containing Y

Mg–7 mass%Gd–x mass%Y (x = 0, 1, 3 and 5) alloys were prepared by casting method, and the microstructures, age hardening behavior and mechanical properties have been investigated. The results show that the addition of Y to the binary Mg–7Gd alloy could reduce the grain size of the as-cast alloys, and enhance the age hardening response and improve mechanical properties during the investigated temperature range. The Mg–7Gd–5Y alloy exhibits maximum ultimate tensile strength and yield strength at peak hardness, and the values are 258 and 167 MPa at room temperature, and 212 and 140 MPa at 250 °C, respectively, which is about 1.8 times as high as the Mg–7Gd binary alloy. When x is more than 3, the amount of Mg₅(Gd,Y) phase is observed at the peak hardness of aged alloys. The significant improvement of the tensile strength at peak hardness is mainly attributed to the fine dispersion of the β-Mg₅(Gd,Y) precipitate.     

Effect of Sn content on microstructure and tensile properties of as-cast and as-extruded Mg−8Li−3Al−(1,2,3)Sn alloys

The effects of Sn content on microstructure and tensile properties of as-cast and as-extruded Mg−8Li−3Al− (1,2,3)Sn (wt.%) alloys were investigated by X-ray diffractometry (XRD), optical microscopy (OM), scanning electron microscopy (SEM) and tensile test. It is found that, as-cast Mg−8Li−3Al−(1,2,3)Sn alloys consist of α-Mg+β-Li duplex matrix, MgLiAl₂ and Li₂MgSn phases. Increasing Sn content leads to grain refinement of α-Mg dendrites and increase in content of Li₂MgSn phase. During hot extrusion, complete dynamic recrystallization (DRX) takes place in β-Li phase while incomplete DRX takes place in α-Mg phase. As Sn content is increased, the volume fraction of DRXed α-Mg grains is increased and the average grain size of DRXed α-Mg grains is decreased. Increasing Sn content is beneficial to strength but harmful to ductility for as-cast Mg−8Li−3Al−(1,2,3)Sn alloys. Tensile properties of Mg−8Li−3Al− (1,2,3)Sn alloys are improved significantly via hot extrusion and Mg−8Li−3Al−2Sn alloy exhibits the best tensile properties.     

Stress corrosion cracking of new Mg–Zn–Mn wrought alloys containing Si

The stress corrosion cracking (SCC) of high strength and ductility Mg–Zn–Mn alloys containing Si was studied using the slow strain rate test (SSRT) technique in air and in 3.5 wt% NaCl solution saturated with Mg(OH)₂. All alloys were susceptible to SCC to some extent. The fractography was consistent with a significant component of intergranular SCC (IGSCC). The TGSCC fracture path in ZSM620 is consistent with a mechanism involving hydrogen. In each case, the IGSCC appeared to be associated with the second-phase particles along grain boundaries. For the IGSCC of the ZSM6X0 alloys, the fractography was consistent with micro-galvanic acceleration of the corrosion of -magnesium by the second-phase particles, whereas it appeared that the second-phase particles themselves had corroded. The study suggests that Si addition to Mg–Zn–Mn alloys can significantly improve SCC resistance as observed in the case of ZSM620. However, the SCC resistance also depends on the other critical alloying elements such as zinc and the microstructure.     

Rolling behaviour of steel backed spray deposited Al–Sn strip

Steel backed Al–10 wt%Sn strip has been prepared by the spray deposition of the molten Al–Sn alloy on a steel substrate, followed by rolling of the resulting composite strip. In the present paper the rolling behaviour of the composite strip at 473 K, together with the characteristics of the spray deposit have been discussed. It has been shown that the Al–Sn spray deposit is a coalesced network of particles having porosity. The particles in the network are of spherical, ligament and irregular shapes. The study shows that the composite metal strip can be rolled well at 473 K without any delamination or surface and edge cracking on the deposit layer. A rolling thickness reduction of 75% produces steel backed Al–10 wt%Sn strip having optimum properties. During rolling, densification in the deposit, deformation in the deposit and substrate, and bonding between the deposit and the substrate take place simultaneously. The mechanism of densification in the deposit layer during rolling has been discussed on the basis of the examination of the microstructure of the deposit at different stages of rolling.     

Ce、Y和Gd对Mg-3Sn-2Sr镁合金铸态组织和力学性能的影响(英文)

通过扫描电镜、X射线衍射、差热分析以及抗拉和蠕变性能测试等手段,调查和比较了Ce、Y和Gd对Mg-3Sn-2Sr镁合金铸态组织和力学性能的影响。结果表明:Mg-3Sn-2Sr三元合金主要由?-Mg、初生和共晶SrMgSn以及Mg2Sn相组成。当添加1.0%Ce、1.0%Y和1.0%Gd到Mg-3Sn-2Sr合金后,合金中分别形成了Mg12Ce、YMgSn、GdMgSn和/或Mg17Sr2相。同时,合金中初生SrMgSn相的形成被抑制,且呈针状的粗大初生SrMgSn相也被变质和细化。此外,添加1.0%Ce、1.0%Y和1.0%Gd均能同时改善Mg-3Sn-2Sr合金的抗拉性能和蠕变性能。在含Ce、Y和Gd合金中,含Ce合金的抗拉性能相对较含Y和含Gd合金的高。     

Effect of directional solidification and heat treatments on the microstructure and mechanical properties of multiphase intermetallic Zr-doped Ni–Al–Cr–Ta–Mo alloy

The effect of directional solidification and heat treatments on the microstructure and mechanical properties of intermetallic Ni–21.29Al–7.04Cr–1.46Ta–0.64Mo–0.57Zr (at.%) alloy was studied. Increasing growth rate is found to decrease primary dendrite arm spacing and to increase volume fraction of β(NiAl)-based dendrites and low melting point γ′(Ni₃Al)/Ni₅Zr eutectic. Room-temperature tensile yield strength and ultimate tensile strength increase and plastic elongation to fracture decreases with the increasing growth rate. Two types of heat treatments of directionally solidified (DS) specimens including two-step ageing at temperatures of 1273 and 1123 K and two-step solution annealing at 1373 and 1493 K were performed. Ageing at 1273 and 1123 K decreases volume fractions of the dendrites and eutectic regions and leads to a coarsening of spherical -Cr and needle-like γ′ precipitates within the β-phase. Annealing at 1373 K for 100 h is shown to be sufficiently long to completely dissolve the eutectic regions. Compressive yield strength increases with increasing temperature reaching a peak value at about 1023 K and then decreases at higher temperatures. Minimum creep rate is found to depend strongly on the applied stress and temperature according to a power law. The power law stress exponent n is determined to be 5.1 and apparent activation for creep Q_a is measured to be 326 kJ/mol.     

AE42合金的抗压入蠕变性能

采用自制实验装置对Mg-Al-2RE(AE42)合金进行压入蠕变实验,利用带能谱(EDS)的扫描电镜(SEM)和X射线衍射(XRD)分析合金蠕变前后的组织和成分的演化.结果表明:随温度或应力的增加,AE42合金的压入蠕变速率和第一阶段的蠕变量逐渐增加;合金在压入状态下的蠕变应力指数和蠕变激活能的均值分别为3.06和72.4 kJ/mol;压入条件下AE42合金的稳态蠕变速率由晶界扩散主导的位错粘滞性滑移控制;铸态AE42合金由α-Mg基体、针状Al11La3和少量颗粒状Al2La组成;固溶处理8 h后,合金中的β-Mg17Al12相溶入α-Mg基体,合金的硬度上升;固溶24 h后,晶粒得到粗化,合金的硬度和抗蠕变性能均下降;固溶处理后再人工时效24 h,晶粒略有细化,但大量β-Mg17Al12相沿晶界不连续析出,合金的硬度和抗蠕变性能进一步下降.     

An electrochemical method for the preparation of Mg–Li alloys at low temperature molten salt system

Mg–Li alloys have been prepared by electrolysis in a molten salt electrolyte of 50% LiCl–50% KCl (mass%) at low temperature of 420–510 °C. The effects of electrolytic temperature and cathodic current density on alloy formation rate and current efficiency were studied. For the deposition of metallic lithium on the cathode consisting of solid Mg and liquid Mg–Li, both electrolytic temperature and cathodic current density have no obvious influence on current efficiency; while for the deposition of metallic lithium on the solid magnesium cathode, both electrolytic temperature and cathodic current density greatly affect alloy formation rate and current efficiency. The optimum electrolysis condition is—molten salt mixture, LiCl:KCl = 1:1 (mass%), electrolytic temperature: 480 °C, cathode current density: 1.13 A cm⁻². Mg–Li alloys with low lithium content (about 25 wt% Li) were prepared via electrolysis at low temperature following by thermal treatment at higher temperature.     

Dependence of Microstructure, Texture and Tensile Properties on Working Conditions in Indirect-Extruded Mg-6Sn Alloys

通过光学显微镜（OM）、扫描电子显微镜（SEM）、X射线衍射仪（XRD）和电子材料试验机研究了反向挤压Mg-6Sn合金的组织、织构和拉伸性能与挤压条件（挤压速度和初始坯料温度）间的依赖关系。研究结果表明：反向挤压 Mg-6Sn 合金的晶粒尺寸、再结晶体积分数和动态析出第二相体积分数在很大程度上取决于反向挤压参数,随着挤压速度和初始坯料温度的升高,合金的织构强度减弱。通过控制挤压速度和初始坯料温度,经高温挤压后的合金表现出最高的抗拉强度。对于商业 AZ31 镁合金而言,合金的强度随着挤压温度的升高而降低。本研究的 Mg-6Sn 合金经高温挤压后的抗拉强度和经低温挤压后的 AZ31 合金相当。上述研究结果表明 Mg-6Sn 合金是一种适合于高速度挤压的新型合金系。     

Microstructure and tribological properties of Cuss-toughened Cr–Cu–Si metal silicide alloys

Wear resistant Cr–Cu–Si metal silicide alloys with different Cu contents were fabricated by the laser melting process. The Cr–Cu–Si alloys have a similar microstructure consisting of the Cr₅Si₃/CrSi dual-phase primary dendrites and the interdendritic Cu-based solid solution (Cu_ss). The Cu content has no effect on the phase constitutions of the alloys. The Cr₅Si₃/CrSi dendrite volume fraction and hardness of the Cr–Cu–Si alloys decrease with the increasing Cu content. Wear test results indicate that all the Cu_ss-toughened metal silicide alloys have excellent wear resistance and low coefficient of friction. Wear resistance increases and friction coefficient decreases with the decreasing Cu content.     

铸态Mg-Sn-Si-Sr合金的显微组织与力学性能

采用X射线衍射仪(XRD)、扫描电镜(SEM)和光学显微镜(OM)分别研究Mg-5Sn-xSi-0.5Sr(x=1,2)和Mg-5Sn-ySi-2Sr(y=1,2)合金的相组成和显微组织,采用力学性能试验机测定合金的拉伸性能。结果表明:Mg-Sn-Si-Sr系合金组织由α-Mg、MgSnSr、Mg2Sn、Mg2Si相所组成。Mg2Si相含量随Si元素的增加而增加,加入Sr元素会促进MgSnSr相的形成,抑制相界上Mg2Sn相的析出。Sn和Sr均能够细化Mg2Si相。当Sr含量由0.5%提高到2%(质量分数)后Mg2Si和Mg2Sn相均能得到显著细化,从而显著提高合金的抗拉强度与屈服强度。     

Microstructure evolution and age-hardening response in Mg-Sn-Sm alloys under a wide range of Sm/Sn ratio

The microstructure evolution and age-hardening response for different Sm/Sn ratios (0–2.55, in wt.%) of Mg-Sn-Sm alloys were investigated. The second phase formation in as-cast alloys and the Mg₃Sm precipitates formed in aged alloys were characterized using XRD, FESEM and HAADF-STEM with EDS techniques. Results indicate that the Sm/Sn ratio has a great influence on the phase constitution, α-Mg grain size and age-hardening response. With the increment of Sm/Sn ratio, Mg₄₁Sm₅ and thermally stable MgSnSm phases precipitate. When the Sm/Sn ratio is about 1.19, the secondary dendrite arm spacing of α-Mg grains significantly decreases. Furthermore, the alloy with Sm/Sn ratio up to 2.55 exhibits the highest age-hardening response, the hardness value increases from 52 HB at solution-treated condition to 74 HB at peak-aged condition (ageing at 220 °C for a short time of 4 h). This is attributed to the large volume fraction of needle-like Mg₃Sm precipitates formed in the α-Mg matrix during ageing treatment, which results in a significant precipitation strengthening effect.