Microstructure and properties of AZ31 magnesium alloy with rapid solidification

Rapidly solidified （RS） AZ31 magnesium alloy ribbons were made using melt spinning technique. The results show that its microhardness increases with the wheel speed, and after heat treatment, the microhardness of the ribbons produced at 1 600 r/min also increases. Rapid solidification leads to reduction of grain size. When the wheel speed reaches 1 600 r/min, no Mg17Al12 phase precipitates, while heat treatment at 200 ℃ leads to precipitation of Mg17Al12 phase. Al-Mn intermetallic compounds with size no larger than 10 nm appear in as-spun ribbons. The corrosion potential of the as-cast ingots is lower than that of the as-spun ribbons.

MICROSTRUCTURE OF Mg-6.4Zn-1.1Y ALLOY FABRICATED BY RAPID SOLIDIFICATION AND RECIPROCATING EXTRUSION

In order to explore the methods to prepare high-strength quasicrystal-reinforced magnesium alloys, the flakes of rapidly solidified Mg-6.4Zn-1.1 Y magnesium alloy with a thickness of 50-60μm were obtained by a melt spinning single-roller device, and the flakes were then processed into rods by reciprocating extrusion and direct extrusion. The microstructure of the alloy was analyzed by optical microscope and SEM, and the constituent phases were identified by XRD. Phase transformation and its onset temperature were determined by differential thermal analyzer （DTA）. The analysis result shows that rapid solidification for Mg-6.4Zn-I.IY alloy can inhibit the eutectic reactions, broaden the solid solubility of Zn in α-Mg solute solution, and impede the formation of Mg3 Y2Zn3 and MgZn2 compounds, and thus help the icosahedral Mg3 YZn6 quasicrystal formed directly from the melt. The microstructure of the flakes consists of the α-Mg solid solution and icosahedral Mg3 YZn6 quasicrystal. Dense rods can be made from the flakes by two-pass reciprocating extrusion and direct extrusion. The interfaces between flakes in the rods can be welded and jointed perfectly. During the reciprocating extrusion and direct extrusion process, more Mg3 YZn6 compounds are precipitated and distributed uniformly, whereas the rods possess fine microstructures inherited from rapidly solidified flakes. The rods contain only two phases： α- magnesium solid solution as matrix and fine icosahedral Mg3 YZn6 quasicrystal which disperses uniformly in the matrix.

Texture Evolutions in Fe-6.5%Si Produced by Rapid Solidification and Chemical Vapor Deposition

Fe-Si ribbons and thin sheets with 6.5%Si content were prepared by means of the single roller rapid solidification and chemical vapor deposition (CVD), respectively. The initial textures of rapidly solidified Fe-6.5%Si ribbons were characteristic of the {100} fiber-type, which became weakened during primary recrystallization in various atmospheres. At the stage of secondary recrystallization, the {100} texture formed in Ar and the {110} texture in hydrogen, while there occurred a texture transformation from the {100} type to the {110} type in vacuum with the increase of annealing temperature. For Fe-6.5%Si sheets prepared by Si deposition in cold-rolled Fe-3%Si matrix sheets, their textures were dominated by the η-fiber (<001>//RD) with the maximum density at the {120}<001> orientations. After homogenization annealing, the η-fiber could evolve into the {130}<001> type or become more concentrated on the {120}<001> orientations, depending on the cold rolling modes of Fe-3%Si matrix sheets.

High Strength, Ductility and Superplasticity Mg-6Zn-1Y-0.6Ce-0.6Zr Alloy Prepared by Rapid Solidification and Reciprocating Extrusion

High strength, ductility, and superplasticity Mg-6.0%Zn-1.0%Y-0.6%Ce-0.6%Zr（wt%） alloy was prepared by sequentially applying rapid solidification, extrusion, and reciprocating extrusion（REX）. The microstructure of the alloy after 2-pass REX consisted of fine grains smaller than 0.7 μm and nanometer strengthening particles. The refined grains resulted from recrystallization during which the nanometer particles played an important role in restrain grain growth. The mechanical properties of the material were investigated at room and elevated temperatures. High tensile yield strength of 336 MPa and elongation of 27% were obtained at room temperature. At elevated temperatures, the highest elongation of 270% was obtained at 250 ℃ and an initial strain rate of 3.3×10^-3 s^-1, and LTS and HSRS were achieved. The high strength, ductility, and superplasticity were attributed to the refined unique microstructure.

Preparation of heat-resistant aluminum alloy pipe blanks by multi-layer spray deposition

A heat resistant aluminum alloy pipe blank with dimensions of d 700/300 mm×1 200 mm was prepared by the multi layer spray deposition technology. Optical microscopy, X ray diffractometry and transmission electron microscopy were used to analyze its morphologies and microstructures. The results show that the microstructures of the pipe blank are homogeneous and the precipitates are uniformly distributed d 25～70 nm spherical or sphere like Al 12 (Fe,V) 3Si particles, its mechanical properties at room temperature and 350 ℃ after densification by extrusion are σ b=412 MPa, δ =7.6% and σ b=187 MPa, δ =7.6%, respectively. The analyses indicate that the proper match of the motion rates of atomizer and substrate can produce deposited blanks with uniform thickness and relatively high cooling rate.

Characterization of microstructure evolution and mechanical properties of the spray-deposited AZ31 magnesium alloy

The cylindrical billets of a Mg-3Al-1Zn （AZ31） alloy were synthesized by spray deposition processing. The microstructure evolution and mechanical properties of the alloy were investigated. The results reveal that the microstructure of the AZ31 alloy is refined significantly by spray deposition processing. A homogeneous and equiaxial-grain structure with an average grain size of 17 μm is obtained. Further grain refinement with an average grain size of 5 μm is attributed to dynamic recrystallization during extrusion processing. The great increase in the density of grain boundary nucleation sites by the finer initial grain sizes makes the dislocation pile-ups near subgrain boundaries being absorbed easily by the boundaries, resulting in an accelerated recrystallization process. The average tensile ultimate and yield strengths of the extruded rods are 321 MPa and 237 MPa, respectively, with an elongation of 15.2% at room temperature, which are remarkably higher than those of the conventional as-cast AZ31 alloy.

MICROSTRUCTURE AND TENSILE PROPERTIES OF RAPIDLY SOLIDIFIED Al－3．8Li－0．8Mg－0．4Cu－0．13Zr ALLOY PREPARED BY SPRAY DEPOSITION

Al-3.8Li-0.8Mg-0.4Cu-0.13Zr alloy was prepared by a novel spray deposition technique,and its microstructure and tensile properties after various aging treatments have been investigated. The experimental results show that the alloy,under study has very fine equiaxed grains about 5-20μm in diameter and a relative density of(94±3)% on average.Grains in the as-extruded alloy are'brick-like'in morphology,and few oxide particles have been found al the grain boundaries.δ' particles with irregular shape and'δ'-β''coprecipitates appear in the aged alloy.The coarsening of δ'particles is fast,and the distance between the particles does not widen so obviously as that of IM(ingot-casting method) alloys with increasing aging time.The spray deposited Al-Li alloy.reaches the peak-aged condition in a short time(10 h al 190℃) when the best properties(σb=534 MPa, σ0.2=480 MPa.δ=10%) are obtained.Compared with RSPM(rapid solidification processing method)Al-Li alloy,the ductility of the tested alloy has been obviously.enhanced while a comparable tensile strength is maintained.

Improving wear resistance of magnesium by droplet spraying of Al-Si alloy

Abstract： In order to improve the surface hardness and wear resistance of magnesium, Al-13%Si （mass fraction） alloy coating was deposited on pure magnesium by droplet spraying process. The microstructure was studied by electron probe microanalysis and X-ray diffraction. The micro-hardness and wear resistance of coating were investigated in comparison with those of the substrate. It is found that the coating layer is composed of a-Al cellular due to rapid solidification. Formation mechanism of the coating is due to the obstruction of diffusion by in-situ formed Mg2Si in interracial layer. The coating exhibits higher hardness compared to that of the Mg substrate. As result of its high hardness, the wear resistance of the coating layer is about ten times that of the substrate. The droplet spraying process demonstrates that the magnesium surface can be strengthened by using the existing Al-Si alloys.

Inherited multimodal microstructure evolution of high-fracture-toughness Mg-Zn-Y-Al alloys during extrusion for the consolidation of rapidly solidified ribbons

The mechanisms of multimodal microstructure evolution and the effects of microstructural factors on mechanical properties must be elucidated to design new alloys with superior properties.In this study,high-fracture-toughness and ductile Mg_(96.75)Zn_(0.85)Y_(2.05)Al_(0.35) alloys were developed using rapidly solidified(RS)ribbon-consolidation technique,and the inherited multimodal microstructure evolution during plastic flow consolidation of the RS ribbons was investigated.The use of extrusion for plastic flow consolidation of the heat-treated RS ribbons produced a multimodal microstructure consisting of the worked grains with high Kernel average misorientation(KAM)angles(Group1),the ultrafine dynamically recrystallized(DRXed)grains with intermediate KAM angles(Group 2),and the fine DRXed grains with low KAM angles(Group 3).Groups 1 and 2 contribute to the alloy strengthening,while Group 3 contributes to improving ductility with strainhardening,resulting in enhancement of the fracture toughness.To form the multimodal microstructure,it was necessary to apply plastic flow with equivalent strains of>2.3 to the heat-treated RS ribbons possessing duplex microstructures with different dispersions of the long-period stacking ordered phase.

Effect of heat treatment on the microstructure and micromechanical properties of the rapidly solidified Mg61.7Zn34Gd4.3 alloy containing icosahedral phase

In this paper, the microstructure evolution of the rapidly solidified (RS) Mg61.7Zn34Gd4.3 (at%, atomic ratio) alloy at high temperatures was investigated. The hardness and elastic modulus of the main precipitated phases were also analyzed and compared with those of the α-Mg matrix on the basis of nanoindentation tests. The results show that the RS alloy consists of either a petal-like icosahedral quasicrystal (IQC) phase (~20 μm) and block-shaped H1 phase (~15 μm) or IQC particles with an average grain size of ~107 nm as well as a small proportion of amorphous phase, which mainly depends on the holding time at the liquid temperature and the thickness of the ribbons. The IQC phase gradually transforms at 400?C to a short-rod-shaped μ-phase (Mg28.6Zn63.8Gd7.7) with a hexagonal structure. The hardness of the IQC phase is higher than that of H1 phase, and both phases exhibit a higher hardness than the α-Mg matrix and the μ-phase. The elasticity of the H1 phase is superior to that of the α-Mg matrix. The IQC phase possesses a higher elastic modulus than H1 phase. The easily formed H1 phase exhibits the poorest plastic deformation capacity among these phases but a higher elastic modulus than the α-Mg matrix.

A NOVEL MULTI－LAYER SPRAY DEPOSITION

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Microstructure and Tensile Properties of Spray Deposited Al-2.15Li-1.28Mg-1.26Cu-0.10Zr Alloy

The microstructure and tensile properties of Al-2. 15Li-1 .28Mg-1 .26Cu-0. 10 Zr alloy processed by a spray deposition processing have been investigated, and experimental results show that the as-deposited Al-Li alloy has a very fine equiaxed grain structure with a relative density of 94±3% on average. Grains in the as-extruded alloy are "brick-like" in morphology, and little oxide particles have been found at the grain boundaries. δ’ particles with irregular shape and, "δ’-β’" co-precipitates precipitate in the aged alloy. S’ phase also precipitate homogeneously at the dislocations. The spray deposited Al-Li alloy has the best properties (σb = 508MPa, σ0.2 = 420MPa, δ=12%) at the peak aged condition. Compared with RS/PM Al-Li alloy, ductility of the tested alloy has been enhanced obviously while a comparable tensile strength is maintained.

Microstructure and mechanical properties of the micrograined hypoeutectic Zn–Mg alloy

A biodegradable Zn alloy, Zn-1.6Mg, with the potential medical applications as a promising coating material for steel components was studied in this work. The alloy was prepared by three different procedures： gravity casting, hot extrusion, and a combination of rapid solidification and hot extrusion. The samples prepared were characterized by light microscopy, scanning electron microscopy, transmission electron microscopy, and X-ray diffraction analysis. Vickers hardness, tensile, and compressive tests were performed to determine the samples＇ mechanical properties. Structural examination reveals that the average grain sizes of samples prepared by gravity casting, hot extrusion, and rapid solidification followed by hot extrusion are 35.0, 9.7, and 2.1 μm, respectively. The micrograined sample with the finest grain size exhibits the highest hardness（Hv = 122 MPa）, compressive yield strength（382 MPa）, tensile yield strength（332 MPa）, ultimate tensile strength（370 MPa）, and elongation（9%）. This sample also demonstrates the lowest work hardening in tension and temporary softening in compression among the prepared samples. The mechanical behavior of the samples is discussed in relation to the structural characteristics, Hall-Petch relationship, and deformation mechanisms in fine-grained hexagonal-close-packed metals.

MICROSTRUCTURES AND MECHANICAL PROPERTIES OF SPUN PIPE BLANKS OF RS AlFeX ALLOY

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Effect of processing parameters on microstructures and mechanical properties of rapidly solidified AlFeVSi hot-extruded product

Rapidly solidified blanks of Al 8.5Fe 1.3V 1.7Si aluminum alloy were prepared by using two methods of cold isostatically pressing of atomized powder and spray deposition of melt metal. Influence of processing parameters, such as extrusion ratio, aspect ratio of cross section of extruded product, extrusion temperature and heating time on microstructures and mechanical properties of rapidly solidified AlFeVSi aluminum alloys was studied by means of optical microscopy, X ray diffractometry, transmission electron microscopy and measurement of tensile properties. Suitable processing parameters were selected to extrude spray deposited blanks into large size pipes. The results show that the effect of extrusion ratio and aspect ratio on microstructures and mechanical properties of rapidly solidified AlFeVSi aluminum alloys can be evaluated by calculating parameter R s, and the value of R s ought to be at least close to 6 in order to obtain high performance extruded product with good binding state. With the increase of extrusion temperature and heating time, the dispersed Al 12 (Fe,V) 3Si particles congregate and coarsen in α (Al) matrix,and the coarse lumpish θ Al 13 Fe 4 phase appears in the alloy extruded above 500 ℃. Therefore, lowering extrusion temperature and shortening exposure time at high temperature through multistage heating are of benefit to changing microstructures and improving mechanical properties of the extruded product. The large size pipes of spray deposited AlFeVSi aluminum alloy extruded at 490 ℃ in the condition of R s being close to 6 and multistage heating have excellent tensile strength and plasticity at room and higher temperature.

多层喷射沉积的装置和原理

为了解决铝合金厚壁管坯、厚板坯和大直径圆锭坯的制备技术问题 ,提出了多层喷射沉积的概念 ,发明了多层喷射沉积技术和一系列装置 ,采用该装置制备出了规格为 Φ外 80 0 mm/ Φ内 3 6 0 mm× 12 0 0 mm,重达10 0 0 kg的耐热铝合金 (80 0 9)管坯 ,Φ70 0 mm× 12 0 0 mm的 6 0 6 6 Al/ Si Cp的复合材料圆柱锭坯 ,管、锭坯冷速达 10 4K/ s,经挤压后性能优异 .研究了多层喷射沉积的过程原理 ,结果表明 ,在多层喷射沉积工艺中 ,金属液滴的沉积轨迹、粘结方式、凝固规律以及工艺特点与传统喷射沉积技术有明显区别 ,多层喷射沉积装置是一种制备大尺寸快速凝固近形坯件的理想装置 .

坩埚移动式喷射共沉积制取铝基复合材料的技术

提出了坩埚移动式喷射共沉积制备铝基SiC颗粒增强复合材料的装置和方法,并与传统的喷射共沉积装置进行了比较.在SiC颗粒增强相加入方法中,新工艺采用了双环缝复合雾化器和螺杆给料负压引流输送装置,解决了大尺寸、高SiC体积百分比复合材料坯制备技术问题.通过上述装置已经制备出Φ800×1000mm,SiC含量为20wt%,重达1t的铝基复合材料.经后续挤压、锻造加工,制备出了性能优异的6000Al/SiCp,FV0812Al/SiCp,7075Al/SiCp的大尺寸复合材料.讨论了喷射共沉积过程中金属液体对SiC颗粒的捕获机理、喷射共沉积过程中的传热与凝固特征,分析了SiC颗粒的加入对金属液粒凝固的影响.

快速凝固镁合金开发原理及研究进展

介绍快速凝固镁合金材料研究与开发的物理冶金原理及发展历程。在开发原理中着重介绍快速凝固镁合金的镁基固溶体扩展、新型弥散合金相的形成、晶粒及显微组织细化以及合金钝化等基础理论。在这些研发理论基础上,进一步阐述镁合金雾化快凝、模冷淬火和表面重熔这3种典型的快速凝固制备技术,举例说明了这3种快速凝固技术制备的多种镁合金的各项性能及显微组织特征。综合评价快速凝固技术制备镁合金材料的优势,说明快速凝固技术是开发新型镁合金材料,扩展镁合金在工程材料中应用的重要且具有发展前途的制备技术。

喷射沉积Al-30Si组织及其半固态保温转变规律

对喷射沉积Al- 30 %Si合金组织及其在半固态保温过程中的转变进行了试验研究 .喷射沉积Al-30 %Si合金沉积态组织是由细小的Si相与α基体组成 ,提出这种组织是由于离异共晶引起的 ,并运用该机制对组织中Si相的集聚进行了解释 ,认为其形成机制为 :其一 ,在沉积阶段凝固过程中大量细小的Si发生了粗化和团聚 ;其二 ,大量的Si在沉积时会发生碰撞而靠在一起 ,在随后的离异共晶凝固过程中 ,共晶硅附着在初生硅上从而将原来相互独立的Si联结在一起 .在半固态保温过程中 ,基体发生熔化而出现球形α ,而Si相则发生粗化 。

喷射沉积Al-Si-Fe-Cu-Mg合金的微观组织和力学行为

对喷射沉积技术制备的Al－Si－Fe－Cu－Mg合金沉积态、挤压态及挤压后热处理态的微观组织进行厂观察和分析，并对合金在后两种状态下的室温和高温拉伸性能进行了测试。