The Structural Evolutions of ZL109 Alloy and 7050 Alloy in the Semisolid Squeeze Casting Process

The structure evolutions of ZL109 alloy and 7050 alloy were studied in the processes of preparing raw billets by low super heat casting, remelting the raw billets, semisolid forming and heat treating components. The thin and symmetrical structure was obtained by using low super heat casting process. The eutectic that lied in the raw billet of ZL109 alloy remelted and produced liquid phase in the process of remelting, but to the 7050 alloy, the eutectic of intergranular and the pointedness of grains was reme...     

Microstructural Evolution and Phase Transformations of Mechanically Stirred Non-dendritic ZA27 Alloy during Partial Remelting

The microstructural evohution and phase transformations of mechanically stirred non-dendriticZA27 alloy during partial remelting were studied by using scanning electron microsccopy and x-ray diffraction technique the partial remelting temperature waw 460℃ and lower than the stirring tenperature of 465℃ so the microstructure with globular grains needed for semi-solid forming can not be obtained and the starting prinary nondendritic grains change in turn to connect non-dendritic grains,long cchain-like structures and fnlly to coursen connect grains houever,the small near-equiaxed grains betueen the primary non-dendritic grains are erohvvl into small globular grains gradtally some of ichich are also attached to the primary non-dendritic grains the subsequent heating the x-ray diffraction results shou that a series of phase transformations α η ε→β，η β →L，β α′ L，α η ε→α′and α′→occur successively during this process the main reuson why the starting primary non-dendritic grains do not occur or occurr incompletely in the layers used to connect the priunary nondendritic grains.     

Thermal-stress simulation of direct-chill casting of AZ31 magnesium alloy billets

Two-dimensional (2D) transient coupled finite element model was developed to compute the temperature and stress field in cast billets, so as to predict the defects of the I-type billets made from AZ31 magnesium alloy and find the causes and solutions for surface cracks and shrinkages during direct-chill (DC) casting process. Method of equivalent specific heat was used in the heat conduction equation. The boundary and initial conditions used for primary and secondary cooling were elucidated on the basis of the heat transfer during the solidification of the billet. The temperature and the thermal-stress fields were simulated with the thermal-structural coupled module of ANSYS software. The influences of casting parameters on the distributions of temperature and stress were studied, which helped optimize the parameters (at pouring temperature of 680 °C, casting speed of 2 mm/s, heat-transfer coefficient of the second cooling equals to 5 000 W/m²·°C⁻¹). The simulation results of thermal stress and strain fields reveal the formation mechanism of some casting defects, which is favourable for optimizing the casting parameters and obtain high quality billets. Some measures of controlling processes were taken to prevent the defects for direct-chill casting billets. Funded by the 973 National Grand Theoretical Research Program(No. 2007CB613700), the National Sci&Tech Support Program(No. 2007BAG06B04), National Natural Science Foundation of China (No. 50725413), and the Natural Science Foundation of Chongqing(No. CST, 2007bb4413)     

Microstructure and mechanical properties of ultrafine grained Mg15Al alloy processed by equal-channel angular pressing

An as-cast magnesium alloy with high Al content Mg15Al was subjected to equal-channel angular pressing (ECAP) through a die with an angle of ϕ=90° at 553 K following route B_c. It is found that the network β-Mg₁₇Al₁₂ phases in the as-cast Mg15Al alloy are broken into small blocks and dispersed uniformly with increasing numbers of pressing passes. Moreover, many nano-sized Mg₁₇Al₁₂ particles precipitate in the ultra-fine α-Mg matrix. The grains are obviously refined. However, the grain structure is inhomogeneous in different areas of the alloy. The average size of the primary phase α-Mg is reduced to about 1 μm while grains of around 0.1–0.2 μm are obtained in some two-phase areas. With additional ECAP passes (up to 8), coarsening of the grains occurs by dynamic recovery. Room temperature tensile tests show that the mechanical properties of Mg15Al alloys are markedly improved after 4 ECAP passes. The ultimate tensile strength and elongation to failure increase from 150 MPa to 269.3 MPa and from 0.05% to 7.4%, respectively. Compared with that after 4 passes, the elongation to failure of the alloy increases but the strength of the alloy slightly decreases after 8 ECAP passes. Fracture morphology of the ECAP-processed alloy exhibits dimple-like fracture characteristics while the as-cast alloy shows quasi-cleavage fractures.     

Microstructure of a spray deposited intermetallic compound alloy of Ni-Al-Mo system

The microstructure of a spray deposited intermetallic compound alloy of Ni-Al-Mo system(Ni3Al-Mo intermetallic compound alloy) prepared by a spray atomization deposition was studied in detail by using optical metallography,XRD,DTA,SEM,TEM,HREM and computer simulation.The preform consists of uniform and equiaxial grains,ranging from 10-40 μm,with some microporosity.Besides the main phases of the matrix alloy γ' and γ,Ni2Mo and Ni3Mo phases are also found within the γ network.A new Ni enriched phase in the γ phase was identified to have face-centered cubic structure with a lattice constant α=1.09 nm and space group Fm3m.     

Microstructural evolution during aging of Ti-5Al-5Mo-5V-1Cr-1Fe alloy

The evolution of microstructure on aging of an (α+β) titanium alloy (Ti-5Al-5Mo-5V-1Cr-1Fe) in the β and (α+β) solution-treated and quenched conditions was investigated. The presence of very fine ω phase was detected by electron diffraction for samples aged below 400 °C. The fine α aggregates are uniformly formed within β grains by nucleating at the ω particles or β/ω interfaces. At higher temperature, the formation of ω phase is avoided and the α lamellae are precipitated at the preferred site of grain boundary and then within the matrix. The highest hardness values are found when the alloys are aged at 450 °C for β condition and 350 °C for (α+β) condition. Foundation item: Project (50634030) supported by the National Natural Science Foundation of China; Project (2007DS04014) supported by the Program of Science and Technology of Shandong Province, China; Project supported by the Open Research Fund from the State Key Laboratory of Rolling and Automation, Northeastern University, China     

Understanding of the influence of process parameters on the heat transfer behavior at the metal/die interface in high pressure die casting process

The current paper focuses on the influence of the process parameters on the peak values of the inter-facial heat transfer coefficient (IHTC) at metal/die interface during high pressure die casting (HPDC) process. A "step shape" casting and AM50 alloy were used during the experiment. The IHTC was de-termined by solving the inverse thermal problem based on the measured temperature inside the die. Results show that the initial die surface temperature (IDST, TDI) has a dominant influence while the casting pressure and fast shot velocity have a secondary influence on the IHTC peak values. By curve fitting, it was found that the IHTC peak value (hmax) changes as a function of the IDST in a manner of hmax =eαTγDI. Such relationship between the IHTC peak value and the IDST can also be found when the casting alloy is ADC12, indicating that this phenomenon is a common characteristic in the HPDC process.     

Hot deformation behavior of Ti-6.5Al-3.5Mo-1.5Zr-0.3Si alloy with acicular microstructure

The characteristics of hot deformation of an α+β titanium alloy Ti-6.5Al-3.5Mo-1.5Zr-0.3Si with acicular microstructure were studied using isothermal hot compressive tests in a strain rate range of 0.01-10 s-1 at 860-1 100 °C. The true stress-true strain curves of alloy hot-compressed in the α+β region exhibit a peak stress followed by continuous flow softening; whereas in the β region,the flow stress attains a steady-state regime. At a strain rate of 10 s-1 and in a wide temperature range,the alloy exhibit...     

Effect of cooling rate on the microstructure of ZA48 alloy

The effect of cooling rate on the microstructure of ZA48 alloy was investigated. The alloy was prepared using a relatively simple technique, i e, rapid cooling of the melt in a steel wedge mould. The dependence of microstructure on the cooling rate (about 40 to 103 K/s) was determined by the secondary dendrite arm space size measurement, optical microscopy(OM), and transmission electron microscopy (TEM). It is found that the matrix structure over a large cooling rate is composed of α-Al dendrite and eutectoid (α+η), the size of α-Al dendrite decreases with increasing cooling rate. The relationship between the cooling rate and the secondary dendrite arm space size has been established. TEM shows that a large number of small and dispersed precipitations can be seen in the primary α phase of tip region. Electron diffraction pattern shows that the precipitate phase is Zn3Mg2 phase.     

Solid-liquid mixed casting of Al-Si alloy

Ａｓｅｒｉｅｓｏｆｎｅｗｔｅｃｈｎｏｌｏｇｉｅｓ ,ｓｕｃｈａｓｓｅｍｉｓｏｌｉｄｍｅ ｔａｌｐｒｏｃｅｓｓｉｎｇａｎｄｓｐｒａｙｆｏｒｍｉｎｇ ,ａｒｅｇｒｅａｔｌｙｄｅｖｅｌｏｐｅｄａｎｄａｐｐｌｉｅｄｉｎｔｈｅｐｒｅｐａｒａｔｉｏｎｏｆａｌｌｏｙｓａｎｄｃｏｍｐｏｓｉｔｅｓｔｈｅｓｅｙｅａｒｓ .Ｉｎａｗｏｒｄ ,ｓｅｍｉｓｏｌｉｄｍｅｔａｌｐｒｏｃｅｓｓｉｎｇ[1 5]ｍａｉｎｌｙｍｅａｎｓｔｈａｔｔｈｒｏｕｇｈｍｅｃｈａｎｉｃａｌｏｒｅｌｅｃｔｒｏｍａｇｎｅｔｉｃａｇｉｔａｔｉｏｎｔｏｔｈｅａｌｌｏ…     

Simulation of dynamic recrystallization for aluminium alloy 7050 using cellular automaton

The prediction of microstructure evolution plays an important role in the design of forging process. In the present work, the cellular automaton (CA) program was developed to simulate the process of dynamic recrystallization (DRX) for aluminium alloy 7050. The material constants in CA models, including dislocation density, nucleation rate and grain growth, were determined by the isothermal compress tests on Gleeble 1500 machine. The model of dislocation density was obtained by linear regression method based on the experimental results. The influences of the deformation parameters on the percentage of DRX and the mean grain size for aluminium alloy 7050 were investigated in details by means of CA simulation. The simulation results show that, as temperature increases from 350 to 450 °C at a strain rate of 0.01 s⁻¹, the percentage of DRX also increases greatly and the mean grain size decreases from 50 to 39.3 μm. The mean size of the recrystallied grains (R-grains) mainly depends on the Zener-Hollomon parameter. To obtain fine grain, the desired deformation temperature is determined from 400 to 450 °C. Foundation item: Project(2005CB724105) supported by the Major State Basic Research Program of China; Project(IRT0549) supported by Program for Changjiang Scholars and Innovative Research Team in University     

Preparation and properties of FeZrB amorphous-nanocrystalline soft magnetic alloy

Fe₆₈Zr₂₀B₁₂ amorphous alloy was prepared by mechanical alloying(MA) method and annealed at different temperatures. Microstructures and magnetic properties of Fe₆₈Zr₂₀B₁₂ alloys as-milled and annealed at 693, 843, 943 and 993 K were studied. The raw powders(Fe, Zr, B) formed b. c. c. α-Fe solid solution at early stages of MA and then transformed into amorphous alloy. Grain size(D) of Fe₆₈Zr₂₀B₁₂ alloys increases with increasing annealing temperature and keeps at nanometer level. The specific saturation magnetization(σ _s ) increases with increasing annealing temperature from 300 K to 943 K, and then decreases with annealing temperature at 993 K because of the precipitation of Fe₃B.     

Mold-filling ability of semisolid alloy

The mold-filling ability of the semisolid alloy has very important effects on the quality and properties of the work pieces produced by the semisolid forming process. The factorial experiments show that all of the heating factors, such as mold temperature, heating temperature and the keeping time of billets, have some effects on the mold-filling ability of semisolid alloy. According to the analysis of influencing extent on the filling ability, it is found that the most important one of the factors is the mold temperature instead of the billets temperature, the next one is the heating temperature of the billet, and the keeping time rows on the third. It is also found that there is an interrelation between the billet heating temperature and the mold temperature. The effect of the interrelation on the mold-filling ability is even stronger than the keeping time. The higher the mold temperature, heating temperature or the keeping time is, the better the mold-filling ability of the semisolid alloy is. The parameter to describe the mold-filling ability, defined as the maximum filling height alongthe upright direction or the maximum filling length along the horizontal direction, can be theoretically determined according to the flowing theory of viscous fuid.     

电脉冲孕育处理对ZL201合金凝固组织的影响

采用新型孕育处理方法—电脉冲孕育处理(简称EPM)技术,对ZL201熔体进行处理,研究其改善合金组织的能力。脉冲电场处理工艺对凝固组织影响的实验结果表明:EPM孕育处理技术可细化ZL201的凝固组织,增加等轴晶数量;合金熔体经EPM孕育处理后,凝固组织中α相之间的共晶组织量有所减少,共晶组织形态呈粒状化,分布均匀。并据此结果,对电脉冲孕育处理技术细化凝固组织及Al2Cu量减少的机理进行了分析。     

Influence of electromagnetic stirring on microstructure of AZ91-0.8%Ce magnesium alloy

1 INTRODUCTION In recent years, magnesium alloys have been used in the automobile industry to save fuel and lower emission levels, and about 60 different types of components of magnesium alloys have been applied in automobile parts, in which AZ91magnesium alloy (Mg-Al system) approximately accounts for 90%[1?4]. It is well known that grain size has very important effect on material properties. According to Hall-Petch equation, when grain size decreases, the mechanical properties such as…     

Investigation of microgravity effect on solidification of medium-low-melting-point alloy by drop tube experiment

The solidification microstructure of Al-Ni, Al-Cu, Ag-Cu, Al-Pb and Cu-Co alloys quenched in silicone oil before and after free fall in evacuated 50 m drop tube were investigated contrastively. The effect of microgravity on the solidification process of medium-low-melting-point eutectic, monotectic and peritectic alloys were analyzed and discussed. The results indicated that the effects of microgravity on the eutectic cell shape, the pattern in eutectic cell and the inter-eutectic spacing were different for different types of eutectic systems; the size distribution of Pb particles in Al-5wt% Pb monotectic alloy was significantly changed by microgravity; and the shape of retained primary α-Co phase in Cu-10wt%Co peritectic alloy was also changed by microgravity. These results are beneficial for people to further identify and analyze the solidification behavior of multiphase alloys under microgravity.     

高温下Al2O3／Al合金复合材料的界面稳定性和拉伸强度

利用挤压铸造制备了Ａｌ２Ｏ３／Ａｌ合金复合材料，研究了高温下复合材料的界面稳定性和拉伸强度，结果表明，在Ａｌ２Ｏ３／ＺＬ１０９复合材料中，纤维与基体之间的界面上发生了化学反应，有利于纤维与基体的结合；在高温下界面层结构稳定，与基体合金相比。Ａｌ２Ｏ３／ＺＬ１０９复合材料具有较好的高温拉伸强度，工作温度可提高１００℃以上，另外，分析了Ａｌ２Ｏ３／ＺＬ１０９复合材料高温拉抻的失效形式。     

Flow stress behavior of Cu13Zn alloy deformed at elevated temperature

Ｃｏｎｓｔｉｔｕｔｉｖｅｍｏｄｅｌｉｓａｍａｔｈｅｍａｔｉｃａｌｒｅｐｒｅｓｅｎｔａｔｉｏｎｏｆｔｈｅｄｅｆｏｒｍａｔｉｏｎｒｅｓｐｏｎｓｅｏｆａｍａｔｅｒｉａｌｔｏｅｘｔｅｒｎａｌｌｙａｐ ｐｌｉｅｄｌｏａｄｉｎｇ ,ｉｎｃｌｕｄｉｎｇｅｎｖｉｒｏｎｍｅｎｔａｌｆａｃｔｏｒｓ .Ｔｈｅｐｒｅ ｃｉｓｅｋｎｏｗｌｅｄｇｅｏｆｔｈｅｃｏｎｓｔｉｔｕｔｉｖｅｂｅｈａｖｉｏｒｏｆｔｈｅｍａｔｅｒｉａｌｉｓｔｈｅｆｏｕｎｄａｔｉｏｎｏｆｎｕｍｅｒｉｃａｌｓｉｍｕｌａｔｉｏｎｔｅｃｈｎｏｌｏｇｙｏｆｍａｔｅｒｉ…     

The Role of Calcium in Microstructural Refinement of AZ91 Magnesium Alloy

The effect of calcium addition on the microstructures of AZ91 magnesium alloy was investigated. It was found that a small amount of calcium in AZ91 allay produced a large decrease in the α- Mg grain size and the dispersed fine β-Mgt7 Alt2 phases. In addition, some Al4Ca particles were found to exist in the AZ91 alloy containing 0.5wt% Ca. EDS analysis and water-quenched technique revealed that the grain-refining mechanism of calcium for the AZ91 alloys was mainly attributed to the role of restricting growth of calcium in the primary α-Mg crystals.     

Microstructure and mechanical properties of an in situ synthesized TiB and TiC reinforced titanium matrix composite coating

A titanium-based composite coating reinforced by in situ synthesized TiB and TiC particles was fabricated on Ti6Al4V by laser cladding. The microstructure and mechanical properties were investigated. The coating was mainly composed of β-Ti cellular dendrites and an eutectic in which a large number of rod/needle-shaped TiB and a few equiaxial TiC particles were homogeneously embedded. The microstructural evolution could be divided into four stages: precipitation and growth of primary β-Ti phase, formation of the binary eutectic β-Ti+TiB, formation of the ternary eutectic β-Ti+TiB+TiC, and solid transformation from β-Ti to β-Ti. Microhardness of the coating showed a gradient variation from the surface (about HV0.2 876) to the bottom (about HV0.2 660) and was prominently improved in comparison with that of the substrate. Fracture toughness of the coating also exhibited a gradient variation from the surface (6.3 MPa·m1/2) to the interface (11.9 MPa·m1/2). Wear resistance of the coating was significantly superior to that of Ti6Al4V.