Phase selection and performance of Mg–Cu–Y amorphous composite with different Mg/Cu ratios

In this article, Mg–Cu–Y alloys with two different Mg/Cu ratios(in at%) were prepared using a watercooled copper mold. Scanning electron microscopy and X-ray diffraction were applied to analyze the microstructure and phase composition. Moreover, corrosion resistance and wear resistance were studied systematically. The results show that both Mg65 Cu25 Y10 and Mg60 Cu30 Y10 alloys could form a composition of crystalline and amorphous phases. Although the microstructure of Mg65 Cu25 Y10 consists of an amorphous phase and a-Mg, Mg2 Cu, and Cu2 Y crystalline phases, the microstructure of Mg60 Cu30 Y10 alloy mainly consists of the amorphous phase and a-Mg, Mg2 Cu. With reducing Mg/Cu ratio, the alloys have better corrosion resistance and wear resistance. The mechanism has also been discussed in detail.     

Evaluation of an Al-Zn-Mg-Li alloy/potential candidate as Al-sacrificial anode

This paper forms part of an overall effort to develop Al-sacrificial In/Hg free anodes; our research has been directed toward developing Al alloys appropriate for cathodic protection. The Al-Zn-Mg system has been particularly selected due to the presence of precipitates in the α-Al matrix, which are capable of breaking down passive films while presenting good electrochemical efficiencies. At the same time, the effect of Li additions on superficial activation of the anode by means of precipitation of AlLi-type compounds was examined. The microstructure was characterized in the as-cast and as-aged ingots, showing the presence of α-Al dendrites as well as eutectic of Al₂Mg₃Zn₃ and precipitates of Mg₇Zn₃ in interdendritic regions. Electron microscopic observations performed on specimens with and without heat treatments showed in the α-Al matrix the presence of a uniform distribution of precipitates of (τ-Al₂Zn₃Mg₃, Mg₇Zn₃, and δ-AlLi type. The electrochemical behavior of the alloy was investigated in a 3% NaCl solution simulating seawater at room temperature. After evaluation of the electrochemical efficiency, values up to 67% were obtained. The relationship between microstructure and electrochemical efficiency is discussed in this work and suggestions of future research are given in order to improve the electrochemical behavior of Al anodes in the field.     

Oxidation of ZC63 Mg alloys reinforced with SiC particles between 390 °C and 500 °C in air

The ZC63 magnesium alloys reinforced with 10 wt.% of SiC particles with an average particle size of 50 μm were cast. The fabricated SiC_p/ZC63 composite consisted of an α-Mg matrix, unreacted α-SiC particles, and an intergranularly formed CuMgZn compound. It was oxidized at 390 °C to 500 °C up to 5 h in air. The oxide scales were thin and compact below 430 °C, but became porous and loose above 450 °C. They consisted primarily of MgO and a small amount of Mg₃N₂. SiC particles were stable over the temperature range explored.     

Diffusion kinetics,mechanical properties,and crystallographic characterization of intermetallic compounds in the Mg–Zn binary system

Pure Mg was diffusion bonded to pure Zn at 315 °C for 168 h to produce equilibrium intermetallic compounds of the Mg–Zn system. All equilibrium phases at 315 °C, Mg₂₁Zn₂₅, Mg₄Zn₇, MgZn₂, Mg₂Zn₁₁, were observed to develop. Concentration profiles by electron probe microanalysis, electron diffraction patterns by transmission electron microscopy, and load–displacement curves by nano-indentation were examined to characterize the phase constituents, crystal structure, diffusion kinetics, and mechanical properties. Mg₂₁Zn₂₅ with trigonal, Mg₄Zn₇ with monoclinic, and Mg₂Zn₁₁ with cubic structures were found and their lattice parameters were reported herein. Mg₄Zn₇ and Mg₂Zn₁₁ were observed to have a range of solubility of approximately 2.4 at% and 1.6 at%, respectively. Interdiffusion in MgZn₂ occurred most rapidly, was an order of magnitude slower in Mg₄Zn₇ and Mg₂Zn₁₁, and was the slowest in Mg₂₁Zn₂₅. Composition-dependence of interdiffusion within each intermetallic phase was negligible. The intermetallic phases exhibited insignificant creep, but evidence of discontinuous yielding was observed. The average hardness and reduced moduli were similar for Mg₂₁Zn₂₅, Mg₄Zn₇, and MgZn₂ phases, ∼5 GPa and ∼90 GPa, respectively. However, the Mg₂Zn₁₁ phase had lower hardness of 3.76 GPa and higher modulus of 108.9 GPa. The mechanical properties in the characterized intermetallic phases, exclusive of Mg₂₁Zn₂₅, were strongly concentration-dependent.     

Effect of the Ca content on the microstructural evolution of Ca containing AZ31 cast alloys

Microstructural changes with varying amounts of Ca in cast AZ31-xCa (x: 0.7 wt.%, 2.0 wt.%, 5.0 wt.%) alloys were investigated. According to transmission electron microscopy (TEM) analyses, it was experimentally confirmed that the C36-(Mg,Al)₂Ca phase with a di-hexagonal structure formed at interdendritic regions in as-cast AZ31 alloys with no more than 2 wt.% Ca. On the other hand, as the Ca content exceeded 2 wt.%, the lamellar structure consisting of the α-Mg phase and the Mg₂Ca phase with a C14 structure formed at interdendritic regions instead of C36 phase. Plate-like Al₂Ca precipitates with a C15 structure also formed on the basal plane inside the α-Mg grains.     

Identification of σ and Ω phases in AA2009/SiC composites

The microstructure evolution during ageing treatment at 170 and 190 °C of AA2009/SiC composites, reinforced with 15 vol.% particulates and whiskers, was studied by transmission electron microscopy. Besides θ′ and S′ phases, the typical hardening precipitates on Al–Cu–Mg alloys, it was found the presence of Ω and σ (Al₅Cu₆Mg₂) phases in the matrix. σ phase was only found in the matrix of particulate composite, while Ω phase appeared in both. This phase has not been previously observed in Al matrix composites based on conventional Al–Cu–Mg alloys.     

Bulk metallic glass formation in the Mg–Cu–Zn–Y system

The element Cu in the bulk glass-forming alloy Mg₆₅Cu₂₅Y₁₀ was substituted with the element Zn to form a Mg₆₅Cu₂₀Zn₅Y₁₀ alloy, which caused a significant improvement of the glass-forming ability of Mg₆₅Cu₂₅Y₁₀ alloy. For the Mg₆₅Cu₂₀Zn₅Y₁₀ alloy, fully glassy rod with a 6-mm diameter can be obtained by copper mold casting.     

Formation of bimodal eutectic structure in Ti63.5Fe30.5Sn6 and Mg72Cu5Zn23 alloys

Microstructural investigation on Ti_63.5Fe_30.5Sn₆ and Mg₇₂Cu₅Zn₂₃ alloys reveals that bimodal eutectic structure containing the synchronization of structural and spatial heterogeneities in the spherical lamellar entity homogeneously forms upon solidification. Furthermore, the bimodal eutectic Ti_63.5Fe_30.5Sn₆ and Mg₇₂Cu₅Zn₂₃ alloys present the enhancement of both strength and plasticity at room temperature compared to the recently developed high strength Ti- and Mg-based alloys. This implies that the bimodal eutectic structure can be one of the effective ways to improve the plasticity of the high strength alloys.     

Microstructure and corrosion behavior of rapidly solidified Mg-Zn-Y alloys

The effect of a minor change in alloy composition on the microstructure and corrosion properties of melt spun Mg_98.3?xZn_xY_1.7 ribbons with x=9–12 is studied by X-ray diffractometry, differential scanning calorimetry, transmission electron microscopy and a dynamic polarization test. The ribbon specimens with x=9–10 revealed an in-situ composite microstructure consisting of icosahedral quasicrystalline phase (I-phase) particles distributed in an α-Mg matrix. The ribbon specimens with x=11 and 12 contained a minor MgZn₂ phase together with an α-Mg phase and I-phase. With increasing Zn content, the corrosion potential increased because of a mixed potential effect, but the formation of a MgZn₂ phase deteriorated the corrosion property through preferential attack, causing an irregular boundary between the corrosion product and the substrate. These results indicate that it is important to control alloy chemistry not to form the MgZn₂ phase in developing an I-phase strengthened Mg-Zn-Y alloy for structural applications.     

Effect of Al addition on microstructure and mechanical properties of Mg−Zn−Sn−Mn alloy

The microstructure and properties of the as-cast, as-homogenized and as-extruded Mg−6Zn−4Sn−1Mn (ZTM641) alloy with various Al contents (0, 0.5, 1, 2, 3 and 4 wt.%) were investigated by OM, XRD, DSC, SEM, TEM and uniaxial tensile tests. The results show that when the Al content is not higher than 0.5%, the alloys are mainly composed of α-Mg, Mg₂Sn, Al₈Mn₅ and Mg₇Zn₃ phases_. When the Al content is higher than 0.5%, the alloys mainly consist of α-Mg, Mg₂Sn, MgZn, Mg₃₂(Al,Zn)₄₉, Al₂Mg₅Zn₂, Al₁₁Mn₄ and Al₈Mn₅ phases. A small amount of Al (≤1%) can increase the proportion of fine dynamic recrystallized (DRXed) grains during hot-extrusion process. The room- temperature tensile test results show that the ZTM641−1Al alloy has the best comprehensive mechanical properties, in which the ultimate tensile strength is 332 MPa, yield strength is 221 MPa and the elongation is 15%. Elevated- temperature tensile test results at 150 and 200 °C show that ZTM641−2Al alloy has the best comprehensive mechanical properties.     

Formation,microstructure and properties of long-period order structure reinforced Mg-based bulk metallic glass composites

In situ Mg–Cu–Y–Zn bulk metallic glass (BMG) matrix composites, in which Mg solid solution flakes of 0.5–1 μm thickness and 2–10 μm length are dispersed, have been prepared by copper mold casting. The Mg flakes are characterized as a long-period order structure (LOS), i.e. periodic arrays of six close-packed planes distorted from the ideal hexagonal lattice of 6H-type. The formation mechanism of LOS is interpreted as the precipitation of the leading phase of the eutectic reaction above the glass transition temperature. In comparison with monolithic Mg-based BMG alloys, the composites with an LOS exhibit significant improvement in mechanical properties, e.g. a compressive plastic strain of ∼18% and ultimate strength of ∼1.2 GPa, have been measured in Mg₈₁Cu_9.3Y_4.7Zn₅ alloy. It is suggested that the enhancement of the mechanical properties of the composites can be attributed to the generation of multiple shear bands and the deformation of the LOS.     

Characterization of High-Frequency Induction Brazed Magnesium Alloy Joint with an Al-Mg-Zn Filler Metal

In this paper, a novel Al-Mg-Zn filler metal was designed to join magnesium alloy AZ31B plates by means of high-frequency induction brazing in argon gas shield condition. The microstructure and the mechanical properties of the brazed joint were investigated. The experimental results showed that the brazed joint contained large amount of α-Mg and β-Mg₁₇(Al, Zn)₁₂ phases. The homogeneous Mg₃₂(Al, Zn)₄₉ phase in the original filler metal was consumed due to the intensive alloying during the brazing process. The results indicate that the shear strength of the brazed joint is 35 MPa. The fracture morphology of the brazed joint exhibits intergranular fracture mode, and the fracture originates from the hard β-Mg₁₇(Al, Zn)₁₂ phase.     

Effect of Y addition on microstructure and mechanical properties of Mg–Zn–Mn alloy

The effects of Y on the microstructure and mechanical properties of Mg–6Zn–1Mn alloy were investigated. The results show that the addition of Y has significant effect on the phase composition, microstructure and mechanical properties of Mg–6Zn–1Mn alloy. Varied phases compositions, including Mg₇Zn₃, I-phase (Mg₃YZn₆), W-phase (Mg₃Y₂Zn₃) and X-phase (Mg₁₂YZn), are obtained by adjusting the Zn to Y mass ratio. Mn element exists as the fine Mn particles, which are well distributed in the alloy. Thermal analysis and microstructure observation reveal that the phase stability follows the trend of X>W>I>Mg₇Zn₃. In addition, Y can improve the mechanical properties of Mg–Zn–Mn alloy significantly, and the alloy with Y content of 6.09% has the best mechanical properties. The high strength is mainly due to the strengthening by the grain size refinement, dispersion strengthening by fine Mn particles, and introduction of the Mg–Zn–Y ternary phases.     

Structure,Properties, and Crystallization of Mg-Cu-Y-Zn Bulk Metallic Glasses

The Mg₆₀Cu₃₀Y₁₀ and Mg₆₅Cu₂₀Y₁₀Zn₅ bulk metallic glasses in the form of a rod 2 mm in diameter were successfully prepared by the conventional Cu-mold casting method. The addition of Zn caused the decrease in the crystallization and melting temperatures in comparison with the Mg₆₀Cu₃₀Y₁₀ alloy. The crystallization and melting temperatures are crucial factors that influence the casting process. An increase in annealing temperature leads to structural changes by the formation of the crystalline phases and lowers the compressive strength. These results obtained for the Mg-based bulk metallic glasses (Mg-BMGs) are important for some practical reasons, in particular, for developing the fabrication process. It has been shown that minor addition of an alloying element can change glass-forming ability and strength of the Mg-BMGs.     

High temperature deformation behavior of Mg-Sn(-Zn) alloy

In the present study, we have investigated the high temperature deformation behavior of Mg-Sn(-Zn) based alloy systems in comparison with that of Mg-Al alloy. Compared with Mg-Al alloy, Mg-Sn alloy exhibits significantly refined grain structure and high ductility due to the presence of fine Mg₂Sn particles in the α-Mg matrix, for example, 184 % at 350 °C under a strain rate of 1 × 10⁻³ s⁻¹. When Zn is added to the Mg-Sn alloy, the elongation to failure remarkably increases from 184 % (Mg-Sn alloy) to 310 % under a strain rate of 1 × 10⁻³ s⁻¹. Such an improvement in ductility is due to the significantly refined grain structure that results from the addition of Zn.     

Effect of Heat Treatment on the Microstructure and Wear Properties of Al–Zn–Mg–Cu/In-Situ Al–9Si–SiCp/Pure Al Composite by Powder Metallurgy

This study examined the effects of heat treatment on the microstructure and wear properties of Al–Zn–Mg–Cu/in-situ Al–9Si–SiCp/pure Al composites. Pure Al powder was used to increase densification but it resulted in heterogeneous precipitation as well as differences in hardness among the grains. Heat treatment was conducted to solve this problem. The heat treatment process consisted of three stages: solution treatment, quenching, and aging treatment. After the solution treatment, the main dissolved phases were η′(Mg₄Zn₇), η(MgZn₂), and Al₂Cu phase. An aging treatment was conducted over the temperature range, 100–240 °C, for various times. The GP zone and η′(Mg₄Zn₇) phase precipitated at a low aging temperature of 100–160 °C, whereas the η(MgZn₂) phase precipitated at a high aging temperature of 200–240 °C. The hardness of the sample aged at 100–160 °C was higher than that aged at 200–240 °C. The wear test was conducted under various linear speeds with a load of 100 N. The aged composite showed a lower wear rate than that of the as-sintered composite under all conditions. As the linear speed was increased to 1.0 m/s, the predominant wear behavior changed from abrasive to adhesive wear in all composites.     

Solidification of Mg-28%Zn-2%Y alloy involving icosahedral quasicrystal phase

Applying XRD, DTA, SEM and TEM techniques, an investigation on the solidification microstructure and solidification sequence of Mg-rich Mg-28%Zn-2%Y （mole fraction） alloy was carried out. It is found that, a-Mg dendrites, Mg7Zn3 phase and icosahedral quasicrystal phase coexist in the as-solidified alloy, where the icosahedral quasicrystal, whose structure is indentified to be a face-centered type, originates from a peritectic reaction occurring at 416 ℃. The primary phase of this peritectic reaction has the composition of Mg20Zn66Y14, which is coincident with the H phase reported by TSAI as （Zn, Mg）5Y. Furthermore, the single I-phase grain morphology was observed and its growth evolution was also discussed.     

Central region of the Mg-Zn phase diagram

The phase equilibria in the Mg-Zn system from 0 to 85 wt pct Zn and from 335° to 93°C have been redetermined. In this region four intermetallic phases, Mg₇Zn₃, MgZn, Mg₂Zn₃, and MgZn₂, exist. Below 325°C, the Mg₇Zn₃ phase decomposes eutectoidally to magnesium solid solution + MgZn. The MgZn phase is stable over the temperature range from 335°C to 93°C; below 325°C, it is in equilibrium with the magnesium solid solution.     

Phase Equilibria of the Mg-Y-Zn System at 500 °C in the Region of < 50 at.% Mg and < 50 at.% Y

The phase equilibria of the Mg-Y-Zn system at 500 °C in the region of?<?50 at.% Mg and?<?50 at.% Y were investigated with heat-treated alloys, by means of the electron probe microanalysis and x-ray diffraction. Seven ternary phases, denoted τ₁ to τ₇, were found to exist in this region, and an additional ternary phase, τ₈, in the more Mg-rich region. The homogeneity ranges of the ternary phases have been well measured. The ternary phases τ₁, τ₂, τ₆, τ₇ and τ₈ are considered to be identical to the previously reported Z-Y₇Mg₂₈Zn₆₅, I-YMg₃Zn₆, W-Y₂Mg₃Zn₃, YMgZn and 10H-Y₄Mg₂₃Zn₃, respectively. The ternary phases τ₃, τ₄ and τ₅ have been found for the first time in the present work. The solubility of Mg in YZn₅ was measured to be up to 25.1 at.% Mg. A partial isothermal section at 500 °C was constructed for the Zn-Mg₂Zn-YMg-Zn region.     

Effect of Mg24Y5 intermetallic particles on grain refinement of Mg-9Li alloy

The microstructures of the as-cast and as-extruded Mg-9Li-xY alloys (x = 0, 0.3; wt%) were observed to investigate the effect of Y on the Mg-9Li alloy, and the crystallographic calculations between Mg₂₄Y₅ and the matrix were examined on the basis of the edge-to-edge matching model. The results indicated that with the addition of 0.3 wt% Y, the average grain size of α-Mg phases in the as-cast Mg-9Li alloy and β-Li phases in the as-extruded Mg-9Li alloy were reduced remarkably, which was caused by the formation of Mg₂₄Y₅ intermetallic compound. Furthermore, crystallographic calculations confirmed that Mg₂₄Y₅ particles were effective grain refiners for both α-Mg and β-Li phases in Mg-9Li alloy.