Comparison about effects of Ce,Sn and Gd additions on as-cast microstructure and mechanical properties of Mg–3.8Zn–2.2Ca (wt%) magnesium alloy

In this paper, the effects of Ce, Sn and Gd additions on the as-cast microstructure and mechanical properties of Mg–3.8Zn–2.2Ca (wt%) magnesium alloy are investigated and compared. The results indicate that adding 1.0 wt% Ce, 1.0 wt% Sn or 1.0 wt% Gd can effectively refine the grains of the Mg–3.8Zn–2.2Ca alloy, and the refinement efficiency of Ce addition is relatively high, followed by the additions of Sn and Gd, respectively. Accordingly, the tensile properties of the as-cast Mg–3.8Zn–2.2Ca alloy are improved by the additions of Ce, Sn or Gd, with the improvement resulting from the Ce addition being best and followed by the additions of Sn and Gd, respectively. In addition, adding 1.0 wt% Ce, 1.0 wt% Sn or 1.0 wt% Gd to the Mg–3.8Zn–2.2Ca alloy can also improve the creep properties of the as-cast alloy. Among the Ce-, Sn- and Gd-containing alloys, the creep properties of the Sn- and Gd-containing alloys are similar but lower than that of the Ce-containing alloy.     

Sc、Zr对Al-Mg-Mn合金再结晶行为及内耗性能的影响

为了研究微量Sc、Zr在Al-Mg-Mn合金中的作用,采用铸锭冶金方法制备了Al-6.0Mg-0.5Mn-(Sc、Zr)合金,通过光学显微镜、显微硬度、透射电镜组织观察和低频扭摆法测量内耗方法研究了微量Sc、Zr对Al-6.0Mg-0.5Mn的组织、再结晶行为及内耗性能的影响.研究表明:添加质量分数为0.21%Sc和0.15%Zr可显著细化Al-6.0Mg-0.5Mn合金铸态组织;粒状Al3Sc1-xZrx相对位错、晶界有强烈钉扎作用,抑制合金再结晶;冷变形后的Al-6.0Mg-0.5Mn-0.21Sc-0.15Zr合金的内耗表现出非线性特征,频率越低或温度越高,合金内耗Q-1越大.在频率为1Hz、应变振幅为4.6×10-5下,冷变形Al-6.0Mg-0.5Mn-0.21Sc-0.15Zr合金升温Q-1-T曲线上在326℃时产生内耗峰,该峰可由Al3Sc1-xZrx沉淀粒子与位错脱钉机制解释.微量Sc、Zr可以细化Al-Mg-Mn合金组织,抑制合金的再结晶,导致合金在升温Q-1-T曲线上产生内耗峰.     

Effects of zirconium addition on as-cast microstructure and mechanical properties of Mg–3Sn–2Ca magnesium alloy

At present, the mechanical properties of the Mg–3Sn–2Ca magnesium alloy are not satisfying and further enhance needs to be considered via further alloying/microalloying additions. The effects of Zr addition on the as-cast microstructure and mechanical properties of the alloy were investigated by using optical and electron microscopies, differential scanning calorimetry (DSC) analysis, and tensile and creep tests. The results indicate that adding 0.41, 0.76 or 1.18 wt.% Zr can refine the grains of the alloy, and the primary CaMgSn phases in the Zr-containing alloys are changed from coarse needle-like net to relatively fine short block and/or particle-like shapes. As a result, the tensile and/or creep properties of the Zr-containing alloys are improved. Among the Zr-containing alloys, the alloy with the addition of 0.76 wt.% Zr exhibits the relatively optimum mechanical properties.     

Effects of minor Zr and Sr on as-cast microstructure and mechanical properties of Mg–3Ce–1.2Mn–1Zn (wt%) magnesium alloy

The effects of minor Zr and Sr on the as-cast microstructure and mechanical properties of the Mg–3Ce–1.2Mn–1Zn (wt%) alloy were investigated. The results indicate that adding minor Zr and/or Sr to the Mg–3Ce–1.2Mn–1Zn alloy does not cause an obvious change in the morphology and distribution of the Mg₁₂Ce phase. However, the grains of the Zr- and/or Sr-containing alloys are effectively refined. Among the Zr- and/or Sr-containing alloys, the grains of the alloy with the addition of 0.5 wt%Zr + 0.1 wt%Sr are the finest. Furthermore, adding minor Zr and/or Sr to the Mg–3Ce–1.2Mn–1Zn alloy can improve the tensile properties. Among the Zr- and/or Sr-containing alloys, the alloy with the addition of 0.5 wt%Zr + 0.1 wt%Sr obtains the optimum tensile properties. In addition, adding minor Zr and/or Sr to the Mg–3Ce–1.2Mn–1Zn alloy also can improve the creep properties, and the creep properties of the three alloys with the additions of 0.5 wt%Zr + 0.1 wt%Sr, 0.5 wt%Zr, and 0.1 wt%Sr are similar.     

The microstructure,mechanical properties and corrosion behaviour of Ce-containing Mg-3Sn-1Ca alloy

The effects of minor Ce on the microstructure, mechanical properties and corrosion behaviour of Mg-3Sn-1Ca alloy are investigated systematically. The minor Ce can refine the eutectic structure between α-Mg and CaMgSn and make the microstructure more uniform. The maximum ultimate tensile strength and elongation of the alloy with the Ce content of 0.3?wt-% were 152.5?MPa and 4.1%, respectively. Meanwhile, the corrosion resistance of the Ce-containing alloys is improved by Tafel curves and electrochemical impedance spectra, especially when the Ce is up to 0.3?wt-%. The minor Ce can promote the formation of the surface film and makes the corrosion product film to become more compact, which effectively prevents further the occurrence of corrosion of the Mg matrix.     

Microstructures and mechanical properties of heat-resistant HPDC Mg-4Al-based alloys containing cheap misch metal

Mg-4Al-xCe/La-0.3Mn (Ce/La: mixture of Ce and La, x = 1, 2, 4 and 6 wt.%) alloys were prepared by high-pressure die-casting. The microstructures, mechanical properties and thermal stability were investigated. The cross-section of test bar could be divided into the fine skin region and the relatively coarse interior region. Two binary Al-(Ce, La) phases with the former being the dominant one, Al₁₁(Ce, La)₃ and Al₂(Ce, La), are mainly distributed along the dendrite boundaries, and La prefers to exist in Al₁₁(Ce, La)₃. The alloy with 4 wt.% Ce/La exhibits high tensile properties and good heat resistance until 200 °C, which were mainly attributed to the fine dendritic arm spacing and the main strengthening phase Al₁₁(Ce, La)₃, which is present in high volume fraction, and possesses fine rod-like morphology, network or “orderly stack” distribution and good thermal stability. The results of this research provide a basis for further investigation of the new low cost high-pressure die-cast Mg-Al-RE alloys designed to serve at temperature up to 200 °C.     

Effects of molybdenum content on the structure and mechanical properties of as-cast Ti-10Zr-based alloys for biomedical applications

The effects of molybdenum on the structure and mechanical properties of a Ti-10Zr-based system were studied with an emphasis on improving the strength/modulus ratio. Commercially pure titanium (c.p. Ti) was used as a control. As-cast Ti-10Zr and a series of Ti-10Zr-xMo (x = 1, 3, 5, 7.5, 10, 12.5, 15, 17.5 and 20 wt.%) alloys prepared using a commercial arc-melting vacuum pressure casting system were investigated. X-ray diffraction (XRD) for phase analysis was conducted with a diffractometer. Three-point bending tests were performed to evaluate the mechanical properties of all specimens. The experimental results indicated that these alloys had different structures and mechanical properties when various amounts of Mo were added. The as-cast Ti-10Zr has a hexagonal α′ phase, and when 1 wt.% Mo was introduced into the Ti-10Zr alloy, the structure remained essentially unchanged. However, with 3 or 5 wt.%, the martensitic α″ structure was found. When increased to 7.5 wt.% or greater, retention of the metastable β phase began. The ω phase was observed only in the Ti-10Zr-7.5Mo alloy. Among all Ti-10Zr-xMo alloys, the α″-phase Ti-10Zr-5Mo alloy had the lowest elastic modulus. It is noteworthy that all the Ti-10Zr and Ti-10Zr-xMo alloys had good ductility. In addition, the Ti-10Zr-5Mo and Ti-10Zr-12.5Mo alloys exhibited higher bending strength/modulus ratios at 20.1 and 20.4, respectively. Furthermore, the elastically recoverable angles of these two alloys (26.4° and 24.6°, respectively) were much greater than those of c.p. Ti (2.7°). Given the importance of these properties for implant materials, the low modulus, excellent elastic recovery capability and high strength/modulus ratio of α″ phase Ti-10Zr-5Mo and β phase Ti-10Zr-12.5Mo alloys appear to make them promising candidates.     

Nanotubular surface and morphology of Ti-binary and Ti-ternary alloys for biocompatibility

The nanotubular surface of Ti-binary and Ti-ternary alloys for biomaterials has been investigated using various methods of surface characterization. Binary Ti-xNb (x = 10, 20, 30, and 40 wt.%) and ternary Ti-30Ta-xNb (x = 3, 7 and 15 wt.%) alloys were prepared by using the high-purity sponges; Ti, Ta and Zr spheres. The nanotube on the alloy surface was formed in 1.0 M H₃PO₄ with small additions of NaF (0.5 and 0.8 wt.%), using a potentiostat. For cell proliferation, an MC3T3-E1 mouse osteoblast was used. The surface characteristics were investigated using field-emission scanning electron microscope, energy dispersive spectroscopy, and X-ray photoelectron spectroscopy.Binary Ti-xZr alloys had a lamellar and a needle-like structure, whereas, ternary Ti-30Ta-xZr alloys had equiaxed grains with a lamellar martensitic α′ structure. The thickness of the needle-like laths of the α-phase increased as the Zr content increased. The nanotubes formed on the α phase and β phase showed a different size and shape appearance with Zr content. As the Zr content increased from 3 to 40 wt.%, the diameter of the nanotubes in Ti-xZr and Ti-30Ta-xZr alloy decreased from 200 nm to 50 nm. The nanotubular Ti-30Ta-15Zr alloy surface with a diameter of 50 nm provided a good osseointegration; cell proliferation, migration and differentiation.     

Effects of Sc Addition and Annealing Treatment on the Microstructure and Mechanical Properties of the As-rolled Mg-3Li alloy

The microstructures and mechanical properties of the as-rolled Mg-3Li and Mg-3Li-1Sc (wt%) alloys before and after annealing treatment have been investigated. Results show that the grains are refined evidently and the recrystallization temperature is improved for more than 100°C by adding 1 wt% Sc into the Mg-3Li alloy. After complete recrystallization, both the strength and ductility of the Mg-3Li alloy are improved evidently with the addition of minor Sc. The brittle fracture tendency of Mg-3Li-1Sc alloy also reduces obviously.     

Effects of Ca addition on as-cast microstructure and mechanical properties of Mg–3Ce–1.2Mn–1Zn (wt.%) magnesium alloy

The effects of Ca addition on the as-cast microstructure and mechanical properties of the Mg–3Ce–1.2Mn–1Zn (wt.%) alloy were investigated by using optical and electron microscopes, differential scanning calorimetry (DSC) analysis, and tensile and creep tests. The results indicate that the additions of 0.3–0.9 wt.%Ca to the Mg–3Ce–1.2Mn–1Zn alloy do not cause an obvious change in the morphology and distribution for the Mg₁₂Ce phase in the alloy. However, the grains and secondary dendrite arm spacings of the Ca-containing alloys are refined, and an increase in Ca amount from 0.3 wt.% to 0.9 wt.% causes the grain size and secondary dendrite arm spacings to gradually decrease, respectively. In addition, the additions of 0.3–0.9 wt.%Ca to the Mg–3Ce–1.2Mn–1Zn alloy can effectively improve the as-cast tensile and creep properties of the alloy, and an increase in Ca amount from 0.3 wt.% to 0.9 wt.% causes the as-cast tensile and creep properties to gradually increase, respectively.     

Mechanical properties and creep of Mg – rare earth – Sc – Mn squeeze cast alloys

The microstructure developed during the T5 treatment of squeeze cast magnesium alloys containing rare earth (Gd, Y, or Ce, ≈ 3–10 wt.%), Sc (< 1 wt.%) and Mn (< 1.5 wt.%) is responsible for a reasonable age hardening in MgGdScMn alloys. Moderate age hardening is only possible in MgY4Sc1Mn1 or MgCe3Sc1Mn1 alloys. The c‐based centred orthorhombic phase precipitating as fine prismatic plates in a triangular arrangement is the most effective hardening phase. The stability of yield strength up to 250°C–300°C was confirmed in T5 treated MgGdScMn and MgY4Sc1Mn1 alloys. All alloys exhibit a reasonable ductility at room temperature. The precipitation of very fine basal discs of Mn₂Sc phase observed in all T5 treated alloys investigated does not contribute considerably to the hardness, but it is very effective in restricting creep. The creep resistance of all alloys investigated is superior to that of commercial WE54 alloy up to 350°C.     

Comparison of the effects of La- and Ce-rich rare earth additions on the microstructure, creep resistance, and high-temperature mechanical properties of Mg-6Zn-3Cu cast alloy

The effect of 1 wt.% La- and Ce-rich rare earth (RE) additions on the microstructure, creep resistance, and high temperature mechanical properties of the Mg-6Zn-3Cu alloy (ZC63) was investigated by impression creep and shear punch tests (SPT). Impression creep tests were performed in the temperature range 423-498 K and under punching stress in the range 150-700 MPa for dwell times up to 3600 s. The ultimate shear strength (USS) was measured by the SPT in the temperature range 298-498 K. The results showed that Ce-rich RE was more effective than the La-rich RE in refining the as-cast microstructure, increasing the number density of eutectic phases at grain boundaries, and producing thermally stable Mg₁₂RE and MgRE compounds. The creep strength of the base alloy was remarkably improved by addition of both types of RE elements, although the Ce-rich RE-containing alloy showed better creep resistance. The addition of La-rich RE increased the shear strength of the base alloy, whereas Ce-rich RE addition had detrimental effects on the shear strength. This was attributed to the formation of a grain boundary network of Mg(Zn,Cu) Laves phases in Ce-rich RE-containing alloy. This grain boundary network with a bulky morphology promoted the initiation and propagation of cracks, leading to an adverse effect on the strength. This was in contrast with its positive influence on inhibiting grain boundary sliding and migration, which enhanced the creep strength of the alloy.     

Microstructure and mechanical properties of Mg -2Gd -3Y -0.6Zr alloy upon conventional and hydrostatic extrusion

The Mg-12Gd-3Y-0.6Zr (wt. %) alloy was subjected to conventional and hydrostatic extrusion in two subsequent steps. The best combination of mechanical properties (strength and ductility) was achieved by RT hydrostatic extrusion following conventional extrusion at 430 °C, with the ultimate tensile strength (UTS), tensile yield strength (TYS) and elongation being 485 MPa, 413 MPa and 5.2% at room temperature. The texture results of extruded rods indicate that the c-axis of most grains was aligned preferentially perpendicular to the extrusion direction, forming a typical extrusion Mg fiber texture.     

Development of Creep Resistant Mg‐Gd‐Sc Alloys with Low Sc Content

High thermal stability and good mechanical properties are crucial for the wider future application of magnesium alloys. One of the most promising directions is the alloying of Mg with rare earth elements as Gd. The fine dispersion of metastable β′ phase (c‐base centred orthorhombic, a = 0.641 nm, b = 2.223 nm, c = 0.521 nm), already known from commercially successful WE alloys (Mg‐Y‐Nd‐Zr), precipitated in all three possible orientation modes during T6 treatment causes very pronounced age hardening in binary Mg‐Gd system and inhibits very effectively the dislocation motion during the creep. The stable β phase (Mg₅Gd, f.c.c. structure, a = 2.234 nm) ensures the creep resistance comparable to WE alloys. A high content of Gd (above 10 wt.%) is necessary to attain the required microstructure. The addition of Sc (below 1 wt.%) and Mn (about 1.5 wt.%) suppresses the solubility of Gd in Mg considerably. The complex precipitation process involving the precipitation of very stable Mn₂Sc, Mn and Gd containing phase and metastable β′ phase is responsible for superior creep properties of MgGd5Sc0.3Mn1 alloy at elevated temperatures. Even at 300°C the creep resistance is markedly better than for WE43 alloy. The increased Gd and Sc contents in MgGd10Sc0.8Mn1 alloy do not further improve the creep resistance.     

Effects of samarium on microstructures and tensile properties of Mg-5Al-0.3Mn alloy

Microstructures and tensile properties of Mg-5Al-0.3Mn-xSm (x = 0, 1, 2 and 3 wt.%) alloys prepared by metal mould casting method were investigated. It was demonstrated that Mg-5Al-0.3Mn alloy was mainly composed of α-Mg and β-Mg₁₇Al₁₂ phases. However, the other two precipitates (Al₁₁Sm₃ and Al₂Sm) were observed along grain boundaries in the alloys containing Sm. The amount of Al₁₁Sm₃ and Al₂Sm precipitates was increased with the increment of Sm content. Meanwhile, volume fraction of β-Mg₁₇Al₁₂ phase was decreased. Moreover, the morphology of β-Mg₁₇Al₁₂ was altered from bulk bone-like shape to spherical one. Tensile results showed that Mg-5Al-0.3Mn-2Sm alloy exhibited the highest tensile properties both at room temperature and 150 °C. Compared with ultimate tensile strength (UTS), yield strength (YS) and elongation (?) of Mg-5Al-0.3Mn alloy, UTS, YS and ? of Mg-5Al-0.3Mn-2Sm alloy were enhanced by 30%, 45% and 35% at room temperature, and by 17%, 48% and 96% at 150 °C, respectively. The improvement of tensile properties was attributed to the decreased amount of β-Mg₁₇Al₁₂ and its refined morphology, and high thermal stable Al₁₁Sm₃ and Al₂Sm precipitates which effectively prohibited dislocation movement and grain boundary sliding during deformation process.     

The effect of 0.5 wt.% Ce additions on the electromigration of Sn9Zn BGA solder packages with Au/Ni(P)/Cu and Ag/Cu pads

It has previously been established that Sn-9Zn-0.5Ce alloy possesses mechanical properties superior to those of undoped Sn-9Zn alloy, and is free of the problem of rapid whisker growth. However, no detailed studies have been conducted on the electromigration behavior of Sn-9Zn-0.5Ce alloy. In this research, Sn-9Zn and Sn-9Zn-0.5Ce solder joints with Au/Ni(P)/Cu and Ag/Cu pads were stressed under a current density of 3.1 × 10⁴ A/cm² at room temperature for various periods of time. Due to finer grain sizes, the electromigration effects were more severe in Sn-9Zn-0.5Ce solder joints than in Sn-9Zn solder joints when joint temperature was around 80 °C. In addition, both solder joints (Sn-9Zn and Sn-9Zn-0.5Ce) with Au/Ni(P)/Cu pads possess longer current-stressing lifetimes than those with Ag/Cu pads because Ni is more resistant than Cu to migration driven by electron flow.     

In-situ observation of the nucleation kinetics and the mechanism of grain refinement in Al-Si alloys (Part I)

The nucleation behavior of primary aluminium phase in a hypoeutectic Al-Si foundry alloy is studied using the 3DXRD microscope during the liquid-solid phase transformation for continuous cooling. Grain nucleation and grain growth for few different casting conditions of a commercial aluminium alloy (A356: Al-7Si-0.4 Mg-0.1Fe-0.1Ti wt.%) were investigated using three dimensional X-ray diffraction microscope (3DXRD) located at ID11 at European Synchrotron Radiation Facility (www.ESRF.eu). To conduct the study a monochromatic hard X-ray beam (energy of 70 keV) with a beam size of 200×200 µm² was used and using a special furnace the microstructure evolution during solidification of a commercial Al-Si foundry alloy (A356) was monitored in-situ. Results gathered from solid fraction information showed adding 0.1 wt.% Ti (as Al-3Ti-B) changes the primary aluminium nucleation temperature and aluminium grain size. Furthermore, it showed that at slower cooling rate (0.04-0.1 K/s) grain refiner can alter the primary aluminium nucleation temperature by 20 °C, whereas at higher rates (2 K/s) this figure was reduced down to 5 °C.     

Gezielte Entwicklung von Magnesiumlegierungen mittels angewandter Thermochemie

No abstract The principle and the methodology of focused alloy development by means of applied thermochemistry are described. The Calphad method is described briefly. As an example, calculations used for applications are shown in the system Mg‐Al‐Sc. In more detail the development of creep resistant alloys in the system Mg‐Mn‐(Sc, Gd, Y, Zr) is discussed. One aim is to produce a sufficiently large quantity of efficient precipitations in the structure in order to improve the mechanical properties with a minimum of expensive alloying addition. The large number of possible combinations of the alloying elements in the system Mg‐Mn‐(Sc, for Gd, Y, Zr) on the one hand and the time and cost of technological experiments on creep stability on the other hand require a preselection of the systems and the alloy compositions. Thermodynamic phase equilibrium and phase amount diagrams were calculated, which give indications on the selection of the promising alloying elements. A priority list of three quaternary systems is produced: Mg‐Mn‐Gd‐Sc, Mg‐Mn‐Sc‐Y and Mg‐Mn‐Y‐Zr. For technical investigations the alloy MgMn1Gd5Sc0.8 (wt.%) is most promising, furthermore the alloys MgMn 1Gd5Sc0.3 and MgMn1Y5Sc0.8 seem promising. Very many other alloys could be eliminated as doubtfull or useless with this method. The entire quaternary Mg‐Mn‐Y‐Zr system was disqualified because of characteristics of the phase diagram, which are harmful for the desired microstructure. This focused alloy development saves time and cost‐intensive technical investigations.     

Influence of forging deformation and heat treatment on microstructure of Ti-xNb-3Zr-2Ta alloys

Ti-xNb-3Zr-2Ta alloys (x = 33, 31, 29, 27, 25) (wt.%) were fabricated by vacuum non-consumable arc melting and hot forging. The hot-forging specimens were solid solution treated at 1053 K for 1.8 ks followed by water quenching (WQ) and air cooling (AC) respectively. The microstructure of hot-forging specimens with different deformation rate and solid solution treated at different temperatures was investigated. The result showed that a large amount of α" martensite appeared in the WQ group while only a little amount of α" phase could be found in the AC group. Moreover, for the WQ group, less niobium resulted in more diffraction peaks of α" phase in XRD profiles. This result suggested that the stability of β phase decreased with the decrease of Nb content. The microhardness of Ti-xNb-3Zr-2Ta (wt.%) alloys was improved significantly with the decreasing Nb content in both WQ group and AC group. Increasing deformation ratio could effectively refine β grains for Ti-25N-3Zr-2Ta (wt.%). Both acicular martensite and lath martensite were found in the transmission electron microscope observation of Ti-25Nb-3Zr-2Ta (wt.%) alloy. Martensitic internal twins were identified as well.     

The effects of trace Sc and Zr on microstructure and internal friction of Zn–Al eutectoid alloy

The damping properties of Zn–22 wt.% Al alloys without and with Sc (0.55 wt.%) and Zr (0.26 wt.%) were investigated. The internal friction of the determined by the microstructure has been measured in terms of logarithmic decrement (δ) using a low frequency inverted torsion pendulum over the temperature region of 10–230 °C. An internal friction peak was separately observed at about 218 °C in the Zn–Al alloy and at about 195 °C in Zn–Al–Sc–Zr alloy. The shift of the δ peak was found to be directly attributed to the precipitation of Al₃(Sc, Zr) phases from the alloy matrix. We consider that the both internal friction peak in the alloy originates from grain boundary (GB) relaxation, but the grain boundary relaxation can also be affected by Al–Sc–Zr intermetallics at the grain boundaries, which will impede grain boundary sliding. In addition, Al–Sc–Zr intermetallics at the grain boundaries can pin grain boundaries, and inhibit the growth of grains in aging, which increases the damping stability of Zn–22 wt.% Al alloy.