Analyzing As-Cast Age Hardening of 356 Cast Alloy

The as-cast age hardening behavior of 356 cast alloy has been investigated by micro hardness measurement, differential scanning calorimetry (DSC), transmission electron microscope (TEM), and electron probe micro analyzer. Age hardening results show that micro hardness value after as-cast aging treatment is almost the same as by T6 treatment, and the solidification rate has little effect on the as-cast age hardening response of 356 cast alloy. DSC and TEM analysis results show that the as-cast age hardening response of 356 cast alloy is attributed to the precipitation of β′ and β″ phases, the high Si concentration in α(Al) contributes about 10 HV to the micro hardness value for samples in as-cast and as-cast aging conditions.     

Effect of Be on aging behavior of an Al-Si-Cu-Mg cast alloy

The effect of Be addition on the aging behavior of UNS 03370 (Al11Si3Cu0.3Mg) was investigated by micro-hardness measurement, differential scanning calorimetry (DSC) and transmission electron microscope (TEM) analysis. Age hardening analysis shows Be additions to an Al11Si3Cu0.3Mg alloy accelerates the age hardening rate and increases the peak hardness by 15 HV during aging at 160°C. DSC shows that Be additions lead to an endothermic peak corresponding to the dissolution of Gunier Preston zones (GP I) disappear with exothermic peaks corresponding to precipitation of GP II zones and the λ′ and/or ϑ′ phases shift to low temperature. DSC and TEM analyses show that GP II zones are more effective than λ′ and/or θ′ on hardening the alloy, and Be addition increases the homogeneous nucleation density of GP II zones. The possible Be atoms participating in the precipitation process during aging and the high Be-vacancy binding energy can explain the effect of Be on aging behavior of Al11Si3Cu0.3Mg alloy.     

In对Al-3.5Cu合金析出过程的影响

利用透射电镜(TEM),差示扫描量热仪(DSC)等方法对Al-3.5Cu和Al-3.5Cu-0.5In(质量分数,%)合金中θ′相的生成及粗化行为进行对比研究。在175℃时效时In的添加显著地促进了合金的时效响应,时效峰值硬度提高了约200MPa。TEM观察结果显示富铟(In′)粒子在时效早期均匀析出,为θ′相的析出提供了非均匀形核位置;且在θ′相宽面发现了位于其片状顶角的In′粒子;时效后期含In合金中θ′相粗化速率明显小于无In合金。时效前增加6%预变形后两种合金时效响应及效果差别不大,证实T6状态In主要是通过淬火空位团簇,从而促进θ′相析出。     

预变形对2E12铝合金时效析出过程的影响

通过DSC热分析、显微硬度测试、透射电镜分析等研究了预变形对2E12铝合金时效析出过程的影响。结果表明：2E12铝合金表现为双阶段时效硬化特征,预变形降低了合金时效第1阶段硬化效果,提高了合金峰时效硬度,缩短了峰时效时间;随预变形量的增加,合金峰时效硬度增大,峰时效时间提前。增加预变形量使合金中析出的板条状S相更为细小、弥散。预变形引入位错对沉淀析出有利,位错环纯刃型位错为S相析出提供有利位置,促进球状S相形核。预变形产生位错结构有利于I型S相析出,并延缓II型S相析出     

Cu含量对Al—Mg—Si合金析出及烤漆硬化行为的影响

采用DSC、硬度测试及TEM研究A16016铝合金中Cu含量对淬火及淬火预时效样品的人工时效析出和硬化行为的影响。结果表明,微量Cu有利于形成较大且稳定性较好的GPI,能在随后的人工时效过程中进一步向GPII转化,从而提高合金的烤漆硬化能力。但是,当Cu含量为0．3％时,烤漆硬化能力没有得到显著增加。对于含Cu合金,预时效热处理也能有效地抑制合金的自然时效行为。     

Oxidation of Amorphous Co75.26−xFe4.74(BSi)20+x Magnetic Alloy

The oxidation characteristics of the Co-rich amorphous magnetic alloy, were investigated. A TEM study of the microstructure revealed a complex oxidation behavior of the alloy depending on composition, especially the boron and silicon concentrations. It was determined that the critical concentration of the metalloid to be 21 at.% above, which a continuous layer of an amorphous borosilicate phase formed on the surface. Phase separation of the surface oxide was also observed when the composition is rich in boron. The metalloid (boron and silicon) concentration was critical in determining the surface-oxide morphology, which in turn, affected the subsurface microstructure. As the magnetization behavior of the Co-rich amorphous alloy depends upon the surface oxide and the internal-oxide precipitates, the guidelines are provided by which one can engineer the microstructure of the alloy to optimize the magnetic properties.     

Effect of Sn on as-cast ageing behavior of Al-Si-Mg alloy

1　INTRODUCTIONTheAl Si basecastalloyshavebeenwidelyusedintheproductionofstructuralcomponentsinengi neeringbecauseofanexcellentcombinationofcasta bilityandmechanicalproperties ,aswellasgoodcor rosionresistanceandweldability .Sandand perma nentcastingswithsolutionandartificialageingheattreatmentweregenerallyneeded ,wherebymetastablephasesprecipitatedfromthesupersaturatedsolution ,whichhardenedthealloy .ThemainstrengtheningelementsincastAl SialloyswereMgandCuandtheagehardeningresponsewass…     

Modeling of Plate-like Precipitates in Aluminum Alloys—Comparison between Phase Field and Cellular Automaton Methods

This report compares two approaches for simulating microstructure evolution of plate-like precipitates during artificial ageing of aluminum alloys: the phase field and the cellular automaton methods. Although both methods are based on thermodynamics, they handle the kinetics in quite different ways, each with its own advantages and disadvantages. Both methods were applied to the growth of semi-coherent plate-like precipitates in Al-4 wt% Cu. Good agreement is found between the results of these two models, as well as experiments. A combination of these two methods would provide a novel approach that is both physically sound and computationally effective for the application of precipitation modeling.     

Precipitate Characteristics and Mechanical Performance of Cast Mg-6RE-1Zn-xCa-0.3Zr (x = 0 and 0.4 wt%) Alloys

In this study, the Mg-4Y-1Gd-1Nd-xCa-1Zn-0.3Zr (x = 0 and 0.4 wt%) cast alloys with low rare earth concentration were prepared in different routes of heat treatments, and their microstructures and mechanical properties were investigated. The Mg-4Y-1Gd-1Nd-1Zn-0.4Ca-0.3Zr cast alloy with ultimate tensile strength (UTS) of 264 ± 7.8 MPa, tensile yield strength (TYS) of 153 ± 1.2 MPa and elongation to failure (EL) of 17.2 ± 1.2% was successfully developed by appropriate heat treatment. The improved mechanical performance was attributed to the combined strengthening effects of fine grains, Mg₂₄RE₅, $\beta ^{\prime}$, $\beta _{1}$, $\gamma ^{\prime}$ and LPSO phases. In the heat treatment process, cooling method of T4 treatment affected the microstructure, which consequently determined the mechanical properties air cooling, rather than water cooling, gave rise to the formation of $\gamma ^{\prime}$ phase in the alloy without Ca addition. However, Ca addition facilitated the formation of $\gamma ^{\prime}$ phase, and the $\gamma ^{\prime}$ phase precipitated in the alloy after T4 treatment either by water cooling or by air cooling, but the air cooling increased the number density of $\gamma ^{\prime}$ phase in comparison to the water cooling. Although the $\gamma ^{\prime}$ phase strengthened the studied alloys, the formation of $\gamma ^{\prime}$ phase inhibited the precipitatition of $\beta ^{\prime}$ and $\beta _{1}$ phases in the following T6 treatment, and consequently reduced the strengthening effect of $\beta ^{\prime}$ and $\beta _{1}$ phases. The results showed that the mechanical performance of the studied alloys was largely determined by the precipitation of $\gamma ^{\prime}$ phase, which was regulated by the Ca addition and the cooling method of T4 treatment.     

Effect of pre-aging on precipitation behavior of Al-1.29Mg- 1.22Si-0.68Cu-0.69Mn-0.3Fe-0.2Zn-0.1Ti alloy

1 Introduction Aluminum alloys of the 6000 series, containing Mg and Si as the major solutes, are strengthened by the precipitation of metastable precursors of the equilibrium β(Mg2Si) phase. The precipitation of these metastable precursors occurs in on…     

Dynamic softening behavior of Al−18Si alloy produced by spray forming

The high-temperature deformation behavior and dynamic softening transition from dynamic recrystallization (DRX) to dynamic recovery (DRV) of Al-18 wt.%Si alloy was studied by torsion tests in a temperature range of 573∼773 K and a strain rate range of 0.001∼1/sec. The alloy was produced by spray-forming followed by hot extrusion. The dependence of flow stress (σ) on strain rate and temperature (T) could be described by the power Arrhenius relationship,. The activation energy and stress exponent values were higher at the low temperature region than those at the high temperature region. The alloy showed a flow curve of DRX in the temperature range of 573∼673 K, while at 673∼773 K, the alloy exhibited a flow curve of DRV. These results were analyzed by observing the shapes of the flow curves throughout the deformation condition. Also, the transition behavior from DRX to DRV has been investigated through observation of deformed microstructure and flow curves during hot deformation.     

淬火析出对Al-Zn-Mg-Cu合金时效行为的影响(英文)

采用硬度测试、光学显微镜(OM)、透射电镜(TEM)和差示扫描量热法(DSC)研究淬火和时效(T6、T7、RRA)对Al-Zn-Mg-Cu合金微观组织的影响。研究发现水淬合金经T6时效后的硬度最高。T7和RRA时效后样品的淬火敏感性相当,较T6时效的高1.2%。TEM观察表明,合金的淬火敏感性主要是由缓慢冷却时非均匀析出引起的。大量η相在再结晶晶粒内的Al3Zr弥散粒子和(亚)晶界上形核,而S和T相在有高密度位错和缺陷的亚结构区生成。时效后,平衡η相周围的η'相更加粗大。经T6、T7、RRA处理后,这些析出相的尺寸和形貌呈现出不同的特征。DSC结果与TEM观察结果一致。T6态的DSC曲线和T7、RRA态的不同,反映了不同的微观组织。     

The effect of an addition of Sc and Zr on the precipitation behavior of AA6061 alloy

The effect of an addition of Sc and Zr on the precipitation behavior of AA6061 alloy was investigated. AA6061 alloy containing Sc and Zr showed different age hardening behavior compared to unadulterated AA6061 alloy. The hardness of the AA6061 alloy peaked when aged for 5 h at 190 °C due to the formation of β″ phases, whereas that of AA6061 alloy containing Sc and Zr peaked at 12 h of aging, and was greater than that of AA6061 alloy when aged for 24 h to 36 h. Thermally stable Al₃(Sc, Zr) phases with a L1₂ structure and low density of β″ phases were found in the Sc- and Zr-added AA6061 alloy aged for 5 h at 190 °C. Transmission electron microscopy (TEM) and differential scanning calorimetry (DSC) revealed that the precipitation rate of the β″ phases was retarded by the addition of Sc and Zr to AA6061 alloy.     

Ternary Diffusion in a RuAl-NiAl Couple

A ternary diffusion couple assembled with NiAl and RuAl disks and annealed at 1100 °C was examined by scanning electron microscopy and analyzed for concentration profiles by electron microprobe analysis. Complete mutual solid solubility with continuous variations in compositions was observed between the binary B2 aluminides. Ternary interdiffusion coefficients were determined with the aid of a program called MultiDiFlux over two composition ranges, one Ru-rich and the other Ni-rich, within the diffusion zone. The interdiffusion coefficient, varies little with variation in composition, but the interdiffusion coefficient, decreases by an order of magnitude from the Ni-rich region to the Ru-rich region. is larger than in the Ni-rich region by an order of magnitude. The cross coefficients, and , are both positive. is comparable in magnitude to the main coefficient in the Ni-rich region; hence, Ni interdiffusion flux is enhanced down a Ru concentration gradient but decreased against it. Similarly, Ni interdiffusion is reduced down Al gradients. Characteristic depth parameters calculated for Ni and Ru are larger on the NiAl side than on the RuAl side. Approximate calculations of cumulative intrinsic diffusion fluxes past a Kirkendall plane suggest that the atomic mobility of Ni is larger than that of Ru.     

Investigation of the structural defects in GaN thin films grown by organometallic vapor phase epitaxy

GaN thin films were prepared on {0001} planes of sapphire substrates by organometallic vapor phase epitaxy (OMVPE) techniques. The crystall orgaphic relation between the film and the substrate as well as the structural features of the defects in the film were investigated by transmission electron microscopy (TEM). Epitaxial relationship was observed in the GaN/sapphire heterostructure preparedin this investigation; (0001) GaN//(0001) sapphire; sapphire. Dislocations of Burgers vector were observed in the film; the propagation behavior of the dislocations exhibits a slip system is operative in the film. Inversion domain boundary (IDB) facets lying parallel to and planes were observed; the type of anti-site bonds (Ga-Ga, N-N) is altemate along these IDB planes, keeping the simple stoichiometry of the compound.     

Effects of cooling rate on solidification behavior of dilute Al-Sc and Al-Sc-Zr solid solution

Six alloys with different compositions of Al-0.1%Sc, Al-0.3%Sc, Al-0.3%Zr, Al-0.1%Sc-0.1%Zr,Al-0.3%Sc-0.1%Zr and Al-0.3%Sc-0.3%Zr were prepared by casting in a wedge shaped copper mould. The hardness test, microstructure observation, and DSC thermal analysis were applied to fully investigate the solidification behavior of the wedge tip (whose cooling rate is 1000 K/s) and the top surface (cooling rate 100 K/s) of each casting. The results show that the cast structures in the hypoeutectic region of AI-Sc alloys are slightly affected by cooling rates during the solidification. In the case of hypereutectic alloy of Al-0.3%Sc-0.3%Zr, the cast grains were remarkably refined under the condition of a 100 K/s cooling rate, however, under a 1000 K/s cooling rate condition,solute atoms contribute nothing to the grain-refinement, due to the eutectic concentration becomes higher. The hardness can be improved to a greater degree by Sc single addition, compared to single Zr addition, but it can be improved even greater when Sc added together with Zr. It is sensitive to cooling rate, the higher the cooling rate, thegreater the hardness. By combining the results of TEM examination and DSC analysis, it can be seen that a supersaturated Al solid solution forms during the solidification, and the solubility of Sc in Al solution can be improved by increasing the cooling rate.     

Texture Evolution in a Warm-Rolled Ti-IF Steel During Cold Rolling and Annealing

The texture characteristics of a Ti-IF steel in ferritic hot-rolled (warm-rolled), cold-rolled, and annealed status were studied. The hot bands were obtained by finish rolling in ferrite region, coiling at very low temperature, and then directly annealing in industrial trial. It was found that dominates at the surface and is the main component at the midsection in the hot band. The α-fiber at the surface as well as at the midsection intensifies during cold rolling and weakens during annealing, while the changing of γ-fiber depends on the hot band texture during cold rolling, but it absolutely intensifies after a well-advanced state of annealing. Orientations concentrate on increasingly at the surface and continuously rotate to RD-fiber at the midsection as the reduction increases. The average plastic strain ratio, elongation, and strain hardening exponent measured for the cold-rolled and annealed steel increased with improving annealing temperatures.     

Effects of Cd and Sn on double-peak age-hardening behaviors of Al-Si-Cu-Mg cast alloys

The effects of trace elements Cd and Sn on precipitation process of Al-Si-Cu-Mg cast alloys were investigated in the present research.It is shown that the addition of Cd and Sn not only increases remarkably the aging peak hardness and reduces the time to reach aging peak,but also eliminates the double-aging-peak phenomenon which appears in Al-Si-Cu-Mg alloys.In Al-Si-Cu-Mg alloys the first aging peak corresponds to GP zones(especially GPⅡ) ,and the second one is caused by metastable phases.The obvious time interval of transition from GPⅡ to metastable phases associates with the double-aging-peak phenomenon.The results of DSC and TEM show that Cd/Sn elements suppress the formation of GPⅠzone,stimulate the formation of θ",θ' and θ phases,and then shorten remarkably the temperature intervals of each exothermic peak.Because the transition interval between GPⅡzone and metastable phases is shortened by Cd/Sn in Al-Si-Cu-Mg cast alloys,θ' phase coexists with θ" phase in matrix of ageing peak condition,which causes effective hardening on the alloys,and at the same time,eliminates the double-aging-peak phenomenon.     

Effects of external stress aging on morphology and precipitation behavior of θ″ phase in Al-Cu alloy

The exposure of Al–5Cu alloy to an external stress with normal aging was carried out. The effects of external stress-aging on the morphology and precipitation behavior of θ″ phase were investigated by transmission electron microscopy (TEM), differential scanning calorimetry (DSC) and first principle calculation. The size of the θ″ phase precipitated plates in stress-aging (453 K, 6 h, 50 MPa) is 19.83 nm, which is smaller than that of those present (28.79 nm) in stress-free aging (453 K, 6 h). The precipitation process of θ″ phase is accelerated by loading external stress aging according to the analysis of DSC results. The apparent activation energy for the external stress-aging is 10% lower than the stress-free one. The first principle calculation results show that the external stress makes a decrease of 6% in the interface energy. The effects of the stress on aging process of the alloy are discussed on the basis of the classical theory. The external stress changes the morphology and precipitation behavior of θ″ phase because the critical nucleation energy is decreased by 19% under stress aging.