Ultrasonic Vibration and Rheocasting for Refinement of Mg–Zn–Y Alloy Reinforced with LPSO Structure

In this work, ultrasonic vibration (UV) and rheo-squeeze casting was first applied on the Mg alloy reinforced with long period stacking ordered (LPSO) structure. The semisolid slurry of Mg–Zn–Y alloy was prepared by UV and processed by rheo-squeeze casting in succession. The effects of UV, Zr addition and squeeze pressure on microstructure of semisolid Mg–Zn–Y alloy were studied. The results revealed that the synergic effect of UV and Zr addition generated a finer microstructure than either one alone when preparing the slurries. Rheo-squeeze casting could significantly refine the LPSO structure and α-Mg matrix in Mg_96.9Zn₁Y₂Zr_0.1 alloy without changing the phase compositions or the type of LPSO structure. When the squeeze pressure increased from 0 to 400 MPa, the block LPSO structure was completely eliminated and the average thickness of LPSO structure decreased from 9.8 to 4.3 μm. Under 400 MPa squeeze pressure, the tensile strength and elongation of the rheocast Mg_96.9Zn₁Y₂Zr_0.1 alloy reached the maximum values, which were 234 MPa and 17.6%, respectively, due to its fine α-Mg matrix (α1-Mg and α2-Mg grains) and LPSO structure.     

流变挤压铸造制备LPSO结构增强Mg-Zn-Y-Zr合金及其组织性能

采用流变挤压铸造工艺制备了含有LPSO结构的Mg99.9-3xZnxY2xZr0.1(x=0.5、1、2,摩尔分数,%)合金,研究了合金的微观组织特征及力学性能。结果表明,流变挤压铸造能有效细化合金的微观组织。合金的基体组织由尺寸较大的α1-Mg和尺寸较小的α2-Mg晶粒组成,LPSO结构呈细小的网状结构均匀地分布在晶界处,LPSO结构的含量越低,其细化效果越明显。随着挤压压力增大,合金中LPSO结构的厚度越来越小,当压力达到100MPa后,厚度变化趋缓。与常规重力铸造相比,流变挤压铸造能有效提高合金的力学性能,特别是伸长率。在400MPa下的流变挤压铸造Mg96.9Zn1Y2Zr0.1合金的抗拉强度和伸长率较重力铸造下分别提高了19%和170%。     

Effect of additional Zn on plasticity of large-scale Mg-based nanostructure-dendrite composites

Large-scale Mg₉₀Cu₁₀ and Mg₉₀Cu₃Zn₇ nanostructure-dendrite composites were successfully fabricated using a water-cooled squeeze casting. The Mg₉₀Cu₃Zn₇ nanostructure-dendrite composite consisting of a mixture of hexagonal α-Mg and tetragonal MgCuZn phases has plasticity up to 8.4 % in excess of that of the Mg₉₀Cu₁₀ nanostructure-dendrite composite consisting of a mixture of hexagonal α-Mg and orthorhombic Mg₂Cu phases. This implies that phase selection plays an important role in controlling the strength and plasticity of large-scale Mg-based nanostructure-dendrite composites.     

Effects of heat treatment on microstructure and mechanical properties of Mg-6Zn-4Sm-0.4Zr alloy

A new rare earth magnesium alloy(Mg-6 Zn-4 Sm-0.4 Zr, wt.%) was prepared by permanent mould casting. The microstructure and mechanical properties of the alloy sample in as-cast and various heat treatment situations were characterized with an optical microscope(OM), X-ray diffractometer(XRD), scanning electron microscope(SEM) equipped with energy dispersive spectroscope(EDS), transmission electron microscope(TEM) and mechanical tests at room temperature, respectively. The experimental results show that the as-cast alloy mainly consists of α-Mg, eutectic Mg_2Zn_3, MgZnSm and Mg_(41)Sm_5. These eutectic phases with continuous or semicontinuous morphology principally distribute along grain boundaries. Almost all the eutectic compounds dissolve in α-Mg and the grains have no obvious growth trend after optimum solution treatment at 490 °C for 18 h. Meanwhile, the ultimate tensile strength(UTS) of 229 MPa and elongation(EL) to rupture of 9.78% can be achieved through the optimal solution treatment, which increase by 37 MPa and 57.74%, respectively, compared with that of the as-cast alloy. Further aging treatments at 200 °C for different durations lead to the conspicuous increment of mechanical properties and prominent age-hardening response. Peak-aged alloy(treated at 200 °C for 12 h) reveals better mechanical properties(UTS 258 MPa, EL 9.42%, hardness 73.4 HV) compared with the same alloy treated in other aging conditions, which is mainly ascribed to precipitated Mg_2Zn_3 and MgZn_2 phases. Fracture analysis demonstrates that the as-cast alloy belongs to inter-granular and cleavage fracture patterns, while the solutionized alloy(treated at 490 °C for 18 h) reveals trans-granular and quasi-cleavage fracture modes. For the peak-aged alloy, the fracture pattern obeys the mixture of trans-granular and cleavage modes.     

Improvement of microstructure,mechanical properties,and corrosion resistance of WE43 alloy by squeeze casting

The WE43 magnesium alloy was prepared by squeeze casting, and the influence of squeeze casting parameters on mechanical properties and corrosion resistance was studied and compared with gravity casting. The gravity cast WE43 alloy shows uneven grain size distribution, and some grains even greater than 90 µm. While, the grain size of the squeeze cast WE43 alloy is mainly distributed in 20–50 µm. The Mg₁₂Nd₂Y phase morphology changes from large lamellar to strips after squeeze casting, whereas Mg₂₄Y₅ phase exhibits no obvious change. The yield strength, tensile strength, and elongation of the gravity cast WE43 alloy are 127 MPa, 157 MPa, and 6%, respectively, and 145 MPa, 193 MPa, and 9.1% for squeeze cast alloy. For the squeeze cast WE43 alloy, the average corrosion rate is 0.6056 mm·year⁻¹ according to immersion test results, and according to electrochemical measurements, the corrosion current density is 78.13 µA·cm⁻², which is better than that of the gravity cast WE43 alloy. Compared with gravity casting, the grains and second phase of the WE43 alloy by squeeze casting are refined, and the mechanical properties and corrosion resistance are improved. This may expand the applications of the WE43 alloy.

     

Effects of cooling rate on microstructure,mechanical and corrosion properties of Mg–Zn–Ca alloy

Mg₆₉Zn₂₇Ca₄ alloys with diameters of 1.5, 2 and 3 mm were fabricated using copper mold injection casting method. Microstructural analysis reveals that the alloy with a diameter of 1.5 mm is almost completely composed of amorphous phase. However, with the cooling rate decline, a little α-Mg and MgZn dendrites can be found in the amorphous matrix. Based on the microstructural and tensile results, the ductile dendrites are conceived to be highly responsible for the enhanced compressive strain from 1.3% to 3.1% by increasing the sample diameter from 1.5 mm to 3 mm. In addition, the Mg₆₉Zn₂₇Ca₄ alloy with 1.5 mm diameter has the best corrosion properties. The current Mg-based alloys show much better corrosion resistance than the traditionally commercial wrought magnesium alloy ZK60 in simulated sea-water.     

超声半固态流变挤压成形Al-20Si-2Cu-0.4Mg-1Ni合金的组织特征(英文)

通过超声振动半固态流变挤压铸造工艺制造汽车空调压缩机铝硅合金斜盘零件,研究合金的组织特征。发现在Al20Si2Cu0.4Mg1Ni合金的组织中,除了通常具有的初晶Si和α(Al)+β-Si共晶相之外,还有非平衡α(Al)颗粒或枝晶。挤压铸造过程中的较快的冷却速度而非压力是非平衡α(Al)相形成的主要原因。在半固态浆料的制备过程中,超声振动的声压作用能促进非平衡α(Al)相在共晶温度以上生成,并生长为非枝晶颗粒。超声处理的过共晶AlSi合金中的非平衡α(Al)相由共晶温度以上生成的圆形α(Al)晶粒和少量共晶温度以下生成的细小α(Al)枝晶构成。由于超声振动的作用使α(Al)基体中的Si的固溶度增加,并使初晶Si的形成温度降低,组织中初晶Si颗粒的体积分数显著降低。流变挤压斜盘中的初晶Si颗粒的平均直径和体积率分别为24.3μm和11.1%。     

Microstructure and mechanical properties of AZ91-Ca magnesium alloy cast by different processes

The microstructure and mechanical properties of magnesium(Mg) alloys are significantly influenced by the casting process. In this paper, a comparative study on microstructure and mechanical properties at ambient and elevated temperatures of AZ91-2 wt.% Ca(AZX912) Mg alloy samples prepared by gravity casting(GC), squeeze casting(SC) and rheo-squeeze casting(RSC), respectively, was carried out. The results show that α-Mg grains in SC and RSC samples are significantly refined compared to the GC sample. The average secondary dendritic arm spacing of AZX912 alloy samples decreases in the order of GC, SC and RSC. As testing temperature increases from 25 °C to 200 °C, strength of AZX912 alloy samples is reduced, while their elongation is increased continuously. Compared to GC and SC processes, RSC process can improve the mechanical properties of AZX912 alloy at both ambient and elevated temperatures. The enhancement of mechanical properties of RSC sample over GC and SC samples mainly results from grain refinement in the as-cast microstructure of AZX912 alloy.     

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.     

Microstructure,mechanical properties and creep resistance of Mg–(8%–12%)Zn–(2%–6%)Al alloys

The microstructural characteristics, mechanical properties and creep resistance of Mg–(8%–12%)Zn–(2%–6%)Al alloys were investigated to get a better overall understanding of these series alloys. The results indicate that the microstructure of the alloys ZA82, ZA102 and ZA122 with the mass ratio of Zn to Al of 4–6 is mainly composed of α-Mg matrix and two different morphologies of precipitates (block τ-Mg₃₂(Al, Zn)₄₉ and dense lamellar ε-Mg₅₁Zn₂₀), the alloys ZA84, ZA104 and ZA124 with the mass ratio of 2–3 contain α-Mg matrix and only block τ phases, and the alloys ZA86, ZA106 and ZA126 with the mass ratio of 1–2 consist of α-Mg matrix, block τ precipitates, lamellar ?-Al₂Mg₅Zn₂ eutectics and flocculent β-Mg₁₇Al₁₂ compounds. The alloys studied with the mass ratio of Zn to Al of 2–3 exhibit high creep resistance, and the alloy ZA124 with the continuous network of τ precipitating along grain boundaries shows the highest creep resistance.     

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.     

The indirect ultrasonic vibration process for rheo-squeeze casting of A356 aluminum alloy

The semisolid slurry of A356 Al alloy was prepared by indirect ultrasonic vibration (IUV) method and then formed by direct squeeze casting (SC). The effects of squeeze pressure and T6 heat treatment on the microstructure and mechanical properties of rheo-squeeze casting (RSC) A356 Al alloy were investigated. The results indicate that with the increase of squeeze pressure, the average diameter of primary α-Al particles decreased, while the densities and mechanical properties of the samples increased. The effect of T6 heat treatment on the mechanical properties is more significant in RSC samples than in conventional SC samples. The tensile strength and elongation of T6 heat treated RSC samples under 100 MPa pressure are 338 MPa and 8%, respectively.     

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.     

热处理对挤压铸造Mg93YZn6合金组织和性能的影响

采用挤压铸造法制备了Mg93YZn6合金,并对其进行高温热处理,分析了铸态和热处理态的Mg93YZn6合金的微观组织、显微硬度和力学性能。结果表明,该合金的挤压铸造和热处理后的组织中均只有α-Mg基体相和准晶I相生成。经500℃×4h热处理后,合金中的准晶相含量与铸态合金中变化不大。经550℃×2h热处理后,合金中的准晶相有所减少。与铸态合金相比,热处理后合金的硬度、抗拉强度和伸长率均提高。     

Peak temperatures and microstructures in aluminium and magnesium alloy friction stir spot welds

Abstract

The peak temperatures during friction stir spot welding of similar and dissimilar aluminium and magnesium alloys are investigated. The peak temperatures attained during friction stir spot welding of Al 6111, Al 2024, and AZ91 are within 6% of their solidus temperatures. In dissimilar AZ91/Al 6111 spot welds the peak temperature corresponds with the α-Mg solid solution and Mg₁₇Al₁₂ eutectic temperature of 437°C. An a-Mg plus Mg₁₇Al₁₂ eutectic microstructure is produced in dissimilar friction stir spot welds when material displaced during pin penetration into the lower sheet material contacts the upper sheet material at the eutectic temperature.     

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.     

含二十面体准晶相Mg-Zn-Y合金的组织和性能

采用常规凝固技术制备了MgZn_6xY_x(x=0.7,1.0,1.5,2.0)合金,研究了Y含量对含有二十面体准晶相(I相)MgZn_6xY_x合金组织和性能的影响。结果表明,MgZn6xYx合金由α-Mg基体和分布在晶界周围的(α-Mg+I相)共晶组织组成。随着Y含量增加,基体晶粒尺寸减小,共晶组织尺寸增大,含量增加,由不连续分布转变为连续分布。在凝固过程中,二十面体准晶相通过共晶转变形成。Mg_89.5Zn_9.0Y_1.5合金的抗拉强度和伸长率达到最大值,分别为179.2MPa和3.5%。MgZn_6xY_x合金的断口呈现准解理断裂特征。     

Mg67Zn28Ca5 bulk metallic glass formation understood via close-packed icosahedron Zn2Mg11 eutectic cluster

Cluster characteristics of Mg₅₁Zn₂₀ binary phase are analyzed using atomic density radial distribution method. Then icosahedron Zn₂Mg₁₁ cluster, having the highest relative atomic density 2.45, is highlighted because of the most close-packed structure. Using cluster-plus-glue-atom model and Zn₂Mg₁₁ cluster, eutectic composition Zn_28.1Mg_71.9 of Mg–Zn binary system can be simply expressed as: [Zn₂Mg₁₁] + (Zn_2.5Mg_0.5). Therefore the most efficient packing icosahedron Zn₂Mg₁₁ is also eutectic-related cluster. Finally, using general cluster formula [cluster](glue atoms)_x(x = 1, 3), Mg-based Mg₆₇Zn₂₈Ca₅ bulk metallic glass may be deciphered via the most close-packed eutectic cluster Zn₂Mg₁₁ as: [Zn₂Mg₁₁] + (Zn₂Ca₁).     

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.     

Effects of trace Cr on as-cast microstructure and microstructural evolution of semi-solid isothermal heat treatment ZC61 magnesium alloy

The content and kind of trace elements in magnesium alloys have important effects on their ascast and semi-solid microstructures. In this research work, effects of trace Cr on as-cast and semi-solid microstructures of ZC61 magnesium alloy were investigated by metal mold casting and semi-solid isothermal heat treatment. The results show that the addition of Cr can refine the α-Mg phase without generating a new phase, noticeably change the eutectic phase, and decrease the average size of solid particles at the same isothermal heat treatment conditions. Non-dendritic microstructures of all alloys are constituted of α_1-Mg phases, α_2-Mg phases and eutectic phases after water quenching. With isothermal temperature increased or holding time prolonged, the eutectic microstructure(α-Mg+MgZn_2+CuMgZn) at the grain boundaries in as-cast alloy is melted preferentially and then turned into semi-solid non-dendritic microstructure by processes of initial coarsening, microstructure separation, spheroidizing and final coarsening. Especially when the ZC61-0.1 Cr alloy was treated at 585 ℃ for 30 min, the ideal non-dendritic microstructure can be obtained, and the corresponding solid particle size and shape factor were 37.5 μm and 1.33, respectively. The coarsening process of solid α-Mg phase at higher temperature or longer time, which is affected by both combining growth and Ostwald ripening mechanism, is refrained when Cr is added to the ZC61 alloy.