Search

Influence of 1.5 wt% Nd addition on microstructures and mechanical properties of the as-extruded Mg−6.0Zn–0.5Zr (ZK60) alloy was studied. The results illustrate that Nd addition clearly refines dynamic recrystallized grains but has almost no influence on texture. Additionally, the intermetallic phases were significantly altered by Nd addition. In ZK60 alloy, the coarse intermetallic phases are MgZn 2 , Mg 21 Zn 25 , Mg 4 Zn 7 , MgZn and I-phase, while MgNdZn 3 (W), Mg 43 Zn 51 Nd 6 (T), MgZn 2 and Nd-enriched MgZn after Nd addition. Also, three kinds of new orientation relationships (ORs) between MgZn 2 or its twin domain and Mg were revealed in this work while both MgZn 2 and W were found to be coherent with T following identical ORs. Furthermore, the fine precipitates are with sizes of ∼20 nm and were confirmed as MgZn 2 , MgZn 2 + MgZn and Mg 4 Zn 7 + MgZn 2 in ZK60 alloy while new spherical Guinier Preston (G.P.) zones with sizes of ∼5 nm after Nd addition. Finally, the above microstructural modifications because of Nd addition result in ultra-high strength for ZK60 alloy, with tensile yield strength being approximately 408 MPa. Image 1 • Nd addition clearly refines DRX grains while with almost no effect on texture. • MgZn 2 , Mg 21 Zn 25 , Mg 4 Zn 7 , MgZn and I-phase were revealed in the ZK60 alloy. • W, Mg 43 Zn 51 Nd 6 (T), MgZn 2 , Nd-enriched MgZn and G.P. zones formed after Nd addition. • Three kinds of new ORs between MgZn 2 or its twin domain and Mg were revealed. • The ZK60 + 1.5Nd alloy exhibits high tensile yield strength of approximately 408 MPa. [ABSTRACT FROM AUTHOR]

Although Mg−Al−RE (RE: rare earth) alloys have significant weight saving potential in automotive industries, their applications were interrupted due to their unsatisfactory mechanical performance. Intermetallic phases in structural magnesium (Mg) alloys are of practical significance for being able to optimize their microstructures for specific applications. Here we report a new alloy design concept that can develop an alloy for a given system with out-standing mechanical performance and low cost. Such designed alloy exhibits even more excellent strength-ductility balance and cost creep-performance than the commercial/experimental die casting Mg alloys and A380 aluminum alloy. The alloy design concept used in this work is based on strictly controlling intermetallic phase components according to modifying alloy's compositions. Such developed alloy has huge potential to be widely applied in automotive powertrain components acted as the alternative of Mg alloys and even aluminum alloys. • A new intermetallic phase was found in a high-pressure die-cast Mg-Al-La system. • Combination of various simulations and experimental results was adopted. • Strengthening mechanisms of the new intermetallic phase were revealed. • Faults were identified based on atomic resolution HAADF-STEM observations. • The newly developed alloy exhibits significantly excellent mechanical properties. [ABSTRACT FROM AUTHOR]

Abstract The electron-carrier-doping effects in an antiferromagnetic insulator Ba 2 MnMoO 6 were investigated by La doping using the first-principles calculation. We examined the magnetic properties and the electronic structures for different doping ratios of La. The results indicate that a transition from an antiferromagnetic (AFM) insulating Ba 2 MnMoO 6 to a AFM half-metallic Ba 2- x La x MnMoO 6 (x ≤ 1.0) and then a AFM metallic phase (x = 1.5, 2.0) occurs upon La doping. The injected electron accommodated into the Mo 4d states accounts for the metallic properties. Moreover, the electron correlation plays a crucial role in the determination of the electronic structure. The evaluated magnetic ordering temperatures for the doping systems are all higher than room temperature revealing the potential applications. Highlights • The magnetic properties of electron doped Ba 2-x La x MnMoO 6 system is determined. • A transition from insulating to half-metallic and then to metallic is obtained. • The magnetic exchange parameter and the magnetic ordering temperature were evaluated. • The virtual atom method is suggested to be accurate and effective. [ABSTRACT FROM AUTHOR]

Abstract The microstructures and mechanical properties of a Mg−8Ho−0.6Zn−0.5Zr alloy were thoroughly investigated. The results reveal five kinds of intermetallic phases, namely the 14H long-period stacking ordered (LPSO) phase, the 18R LPSO phase, Mg 24 Ho 5 , Mg 0.5 Ho 1.5 , and Mg 3 Ho. Ordinarily, the 18R LPSO phase locates at a lamellae grain boundary with the misorientation angle of 136.9° and is simultaneously coherent with two α-Mg grains. The corresponding orientation relationships are as (001) 18R //(0001) α1 and [010] 18R //〈11 2 ¯ 0〉 α1 , and (001) 18R about 43.1° from (0001) α2 and [010] 18R //〈11 2 ¯ 0〉 α2. After hot-extrusion, the disintegrated intermetallic phases composed of Mg 24 Ho 5 and Mg 3 Ho mainly distribute at extrusion stringers while the LPSO phases mainly locate in un-recrystallized regions. In addition, amounts of fine spherical intermetallic particles were formed when many parallelly distributed LPSO plates precipitated in a part of the recrystallized grains. The as-extruded Mg−8Ho−0.6Zn−0.5Zr alloy exhibits excellent combination of high strength and high ductility. The underlying strengthening mechanisms were revealed as fine-grain strengthening and dispersion strengthening. Highlights • Microstructures and mechanical properties of a Mg−Ho−Zn−Zr alloy were investigated. • Five intermetallic phases including both 14H and 18R LPSO phases were observed. • 18R LPSO phase at a new lamellae GB is simultaneously coherent with two α-Mg grains. • Fine H1 phase which are coherent with Mg matrix was formed after hot-extrusion. • The as-extruded alloy exhibits excellent combination of high strength and ductility. [ABSTRACT FROM AUTHOR]

The types and structures of the intermetallic phases formed during solidification in an as-cast Mg−4Al−15Gd−4Y−1Zn alloy were systematically investigated in detail using transmission electron microscopy (TEM). The results indicate that both 14H- and 18R-long period stacking-ordered (LPSO) phases are clearly different from the conventional LPSO phases in the Mg−TM−RE (TM = transition metal) systems and with the order-disorder structures. Furthermore, these two LPSO phases occasionally coexisted with each other following an orientation relationship as (0014) 14H about 70.6° from (0018) 18R and [1 1 ¯ 00] 14H //[1 1 ¯ 00] 18R . In addition, another six intermetallic phases namely the large and the small blocky phases on grain boundary, the short and the long parallel plates near grain boundary, the large lamellae phase with irregular profile and the small lamellae phase coexisted on the 18R-LPSO phase were found in the studied alloy. The former three phases are Mg 5 RE phase and the later three phases are 14H-LPSO, Mg 4.8 Al 12 RE 7.2 and Mg 24 RE 5 , respectively. Finally, the special 18R-LPSO phase in the studied alloy may be transformed from the Mg 4.8 Al 12 RE 7.2 phase following an orientation relationship as (0018) 18R //(111) Mg4.8Al12RE7.2 and [1 1 ¯ 00] 18R //[0 1 ¯ 1] Mg4.8Al12RE7.2 . [ABSTRACT FROM AUTHOR]

• Wrought Mg-Zn-Al-Gd alloy with good tensile/compressive strength and ductility was prepared. • Four intermetallic phases namely ϕ , τ , i and Al 2 Gd are dominant in the as-cast sample. • This alloy has a fully recrystallized microstructure with the average grain size of ~1.5 µm. • Fine i -phase particles were quite homogeneously dispersed in the fine-grained structure. Microstructural evolution and mechanical properties of a Mg−8Zn−6Al−1Gd (wt%) alloy were thoroughly investigated in this work. The results indicate that the dominant intermetallic phases in the as-cast sample are ϕ -Al 2 Mg 5 Zn 2 , τ -Mg 32 (Al,Zn) 49 , i -Mg 44 Al 15 Zn 41 and Al 2 Gd phases and almost free Gd was detected in the former three phases. After extrusion, the sample has a fully recrystallized microstructure with the average grain size being ~1.5 µm, and exhibits a weak rare earth texture. Additionally, fine particles were approximately homogeneously dispersed in the fine-grained structure. Most of them are quasicrystal phase (i -phase) but have no identical orientation relationship with Mg matrix regardless of whether they distribute at grain boundaries or inside grains. Finally, the as-extruded sample exhibits good strength-ductility balance in both tension and compression and simultaneously has a slight reverse tension/compression asymmetry. Microstructural observations indicate that the excellent mechanical performance of the studied alloy is highly related to its fine grains, weak RE texture, and numerous homogeneously distributed fine particles. [ABSTRACT FROM AUTHOR]

• Minor La addition significantly increases the dynamic recrystallization. • No new intermetallics except Mg 17 La 12 were introduced after La addition. • La addition achieves high yield strength of 480 MPa and high ductility of ~6%. • Grain refinement by recrystallization is the key to good strength-ductility. Effects of 0.5 wt% La addition on microstructures and mechanical properties of a traditional hot-extruded Mg–9Gd–3Y–0.5Zr alloy were thoroughly investigated in this work. The results indicate that minor La addition obviously improves the alloy's mechanical performance at room temperature, accomplished an ultra-high tensile yield strength of 480 MPa with the elongation of ~6%, although leading to much lower high-temperature strength. Microstructural analysis reveals that after extrusion, minor La addition leads to a significantly higher level of recrystallization (the volume fraction is improved from 21% to 68%), much finer dynamically recrystallized (DRXed) grains (the average sizes are refined from 4.12 µm to 3.26 µm), and also finer non-recrystallization stripes. La addition promoting recrystallization is mainly attributed to the finer grains and much more intermetallics not only at grain boundaries but also in α-Mg grains of the ingots before extrusion. During peak-aging, minor La addition does not change intermetallics/precipitates in both DRXed grains and non-recrystallized regions except some extra coarse Mg 17 La 2 particles mainly in extrusion stringers. Therefore, minor La addition improving both strength and ductility of the hot-extruded Mg–9Gd–3Y–0.5Zr alloy at room temperature is mainly by grain-refinement strengthening which is also the underlying cause for the lower work hardening coefficient, high-temperature strength but higher ductility. [ABSTRACT FROM AUTHOR]

Microstructures of the Mg−8Gd− x Yb−1.2Zn−0.5Zr (x = 0, 1, 2, 3, and 4, in wt.%) alloys prepared by gravity permanent mold casting were investigated. The results indicate that the components of intermetallic phases are closely depended on the content of Yb additions. Firstly, the eutectic phase in the alloy with free Yb addition is Mg 3 Gd. As the Yb addition increases, Mg 5 (Gd,Yb) and Mg 12 (Gd,Yb) eutectic phases successively formed. Furthermore, both Mg 5 (Gd,Yb) and Mg 12 (Gd,Yb) are coherent with Mg 3 (Gd,Yb) following orientation relationships (ORs) as: (200) Mg3(Gd,Yb) //(200) Mg5(Gd,Yb) , [001] Mg3(Gd,Yb) //[001] Mg5(Gd,Yb) , and (002) Mg3(Gd,Yb) //(006) Mg12(Gd,Yb) , [010] Mg3(Gd,Yb) //[010] Mg12(Gd,Yb) , respectively. Then, the volume fractions of Mg 5 (Gd,Yb) and Mg 12 (Gd,Yb) gradually increase as the Yb content increases. When the Yb addition is over 3 wt.%, the Mg 5 (Gd,Yb) phase becomes the dominant eutectic phase. Finally, the volume fraction of 14H-type long-period stacking ordered (LPSO) phase which mainly distributes in the regions near grain boundaries clearly decreases as the Yb content increases. • Microstructure evolutions of Mg−8Gd− x Yb−1.2Zn−0.5Zr alloys were investigated. • Mg 5 (Gd,Yb) and Mg 12 (Gd,Yb) phases successively formed as the Yb content increases. • Both Mg 5 (Gd,Yb) and Mg 12 (Gd,Yb) coexist with and are coherent with Mg 3 (Gd,Yb). • As Yb addition increases, the volume fraction of Mg 5 (Gd,Yb) and Mg 12 (Gd,Yb) increases. • The volume fraction of Mg 3 (Gd,Yb) and LPSO phase decreases as Yb addition increases. [ABSTRACT FROM AUTHOR]

Abstract Coexistence of 14H and 18R-type long-period stacking ordered (LPSO) phases was observed in a cast Mg−Al−RE−Zn alloy, following a novel orientation relationship of (0001) 14H about 70.5° from (001) 18R and [1 1 ¯ 00] 14H //[100] 18R. Transmission electron microscopy (TEM) observations reveal that this novel structure was formed because of the concurrence of the precipitation of 18R structure in the lumpy Mg 4.8 Al 12 RE 7.2 phase and the heterogeneous nucleation of 14H structure on the coherent Mg/Mg 4.8 Al 12 RE 7.2 interface during isothermal heat treatment at 300 °C. This paper gives an in depth understanding of the new formation mechanisms of the coexistence of both 14H and 18R-type LPSO phases. Highlights • Coexistence of 14H and 18R-type LPSO phases was observed in a cast alloy. • A novel OR was revealed: (00014) 14H about 70.5° from (0018) 18R , [1 1 ¯ 00] 14H //[100] 18R. • Both 14H and 18R-type LPSO phases are formed related to the Mg 4.8 Al 12 RE 7.2 phase. • The 18R-type LPSO phase precipitated in the lumpy Mg 4.8 Al 12 RE 7.2 phase. • The 14H-type LPOS phase only nucleated on the coherent Mg/Mg 4.8 Al 12 RE 7.2 interface. [ABSTRACT FROM AUTHOR]

An ultrathin wall Mg-8Zn-8Al (wt%) alloy was manufactured by high-pressure die casting (HPDC), and exhibits standout strength of ∼ 248 MPa with an acceptable elongation of ∼2.3%. Interestingly, this alloy contains relatively coarse α-Mg grains (∼ 5.6 µm) and ultra-fine β-Mg grains (∼ 0.67 µm), and many nano-sized icosahedral quasicrystal phase (I-phase) particles in eutectic regions. Atomic-resolution high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) observations reveal possible amorphous regions around I-phase particles, C-containing phase and/or MgO aggregations, and Zn-rich clusters and pyramidal precipitates. Both ultra-fine grains along with the skeleton consisted of nano-sized I-phase particles and solutes including Zn-rich clusters in Mg matrix contribute the ultra-high strength. On the other hand, this work indicates that interaction of alloy melt with CO 2 is avoidless during ultra-thin wall HPDC and pyramidal precipitation is possible at least in Zn-containing magnesium alloys. • An ultrathin wall Mg-Zn-Al alloy was manufactured to have ultra-high strength. • It contains coarse α-Mg grains (∼ 5.6 µm) and ultra-fine β-Mg grains (∼ 0.67 µm). • Intermetallic skeleton is consisted of nanosized I-particles and amorphous areas. • Novel C-containing phase and pyramidal precipitate are firstly reported in Mg. [ABSTRACT FROM AUTHOR]