SCR技术制备A2017合金半固态材料组织演化

采用SCR(shearing-cooling-roll)技术制备了A2017半固态合金, 对合金液在不同温度下进行浇注, 且对辊-靴型腔中合金组织的演化过程进行了跟踪, 分析了SCR过程中凝固形核的热力学条件以及层流剪切特性.结果表明: 随着合金液浇注温度的降低, 坯料内部组织从粗大的枝晶或菊花晶转化为细小的近球形晶.合金液首先在轧辊和靴子表面结晶形核, 在液流冲击及剪切的作用下, 晶核从型壁上脱落进入残余液相形成游离晶; 随着辊-靴型腔内合金固相率的增加, 游离晶在以枝晶方式生长过程中受到层流剪切作用, 二次枝晶臂断裂破碎形成自由晶; 自由晶在层流剪切作用下进一步发生碰撞和摩擦, 最后逐渐趋于球形或椭球形.     

蛇形通道浇注制备半固态浆料组织的演化

采用蛇形通道浇注制备7075铝合金半固态浆料,研究了不同浇注温度下浆料组织中初生α-Al的形貌演变,通过残留在蛇形通道内部的凝固壳分析了蛇形通道内部合金熔体的形核动力学条件,自由晶的形成、长大与球化机理。结果表明:自由晶的数目决定了初生α-Al的形态,随着浇注温度降低,过冷度的增大,浆料组织中的初生α-Al的形貌由蔷薇状向近球状转变,晶粒尺寸逐渐变小,晶粒数目增多;蛇形通道内过冷的合金熔体经过弯道的作用,熔体内部的对流、剪切和"搅拌"使初生激冷α-Al晶核经过游离、增殖、长大和熟化,最后演变成近球状和蔷薇状的α-Al晶粒;球状初生α-Al晶粒的演变机制主要为枝晶抑制生长机制,也包括枝晶臂根部熔断机制。     

SCR技术制备2A11兰固态合金的研究

在介绍单辊剪切／冷却技术制备半固态2A11合金材料原理的基础上，提出了半固态2A11合金球形晶粒组织形成的新观点；被晶破碎与内液体合金形核形成自由晶，自由晶自由运动生长而球化。研究分析表明：烧注温度、冷却强度、轧辊转速与辊靴表面性质影响半固态2A11合金组织。     

SCR技术制备半固态合金非枝晶组织形成机制

采用单辊搅拌冷却技术制备A2017半固态合金,对半固态合金非枝晶的形成及演变过程进行了研究.结果表明,随着合金熔体浇注温度的降低或者辊靴行腔高度的减小,半固态合金组织逐渐从粗大的枝晶转变为细小的等轴晶.从辊靴行腔入口到出口,靠近靴子面侧半固态合金组织依次为枝晶、退化枝晶和等轴晶,而靠近工作辊面侧合金组织主要为细小的等轴晶和球形晶.合金组织的演变过程为合金熔体首先在靴子和工作辊内表面凝固形核并长大成枝晶,在工作辊的剪切搅拌作用下,枝晶从辊靴表面破碎脱落进入熔体,在工作辊对高固相率半固态合金的剪切搅拌下,枝晶进一步发生断裂破碎最终形成细小的等轴晶和球形晶.     

脉冲电流作用下TiAl合金凝固组织演变及形成机理

利用OM和TEM研究了脉冲电流作用下Ti-48Al-2Cr-2Nb合金的凝固组织,并分析了其微观组织演变及形成机理。结果表明,脉冲电流细化了TiAl合金的一次枝晶臂间距、柱状晶尺寸和片层间距。未加载电流的TiAl合金凝固的初生相为α相,TiAl合金的片层取向与柱状晶生长方向夹角较大,甚至垂直于生长方向。脉冲电流作用导致枝晶发生熔断和破碎,促进了β枝晶相的析出及增多,片层取向与晶体生长方向夹角较小或成45°生长的片层进一步增多。脉冲电流降低了固-液相之间的自由能及原子扩散激活能,减少形核位垒及晶核的形核功,从而在一定程度上促进原子扩散,增大了形核率,细化一次枝晶臂间距及柱状晶;初生相的转变析出及其特殊的位向关系是片层取向变化的主要原因。     

AZ61镁合金连续流变成形过程的组织演化行为

采用自行设计的连续流变挤压成形设备成功制备出声10mm的AZ61镁合金线材。合金从辊靴型腔人口到出口的过程中，受到轧辊的剪切作用，枝晶臂不断受到剪切破碎，合金从浇注口到挤压区，逐渐由发达的枝晶状组织演化为细小的破碎晶、等轴晶和球形晶。在挤压成形时，中心部位固相变形小，边部大，在圆弧流动区产生了优良的超细晶组织。在合理的技术条件下，制备的AZ61合金线材断面组织优良，呈现两相塑性流动的特征。     

低压脉冲电流下AZ91D镁合金半固态组织形成机理研究

在不同凝固阶段合金的半固态组织和脉冲电流热效应的实验研究基础上,探讨了低压脉冲电流下AZ91D镁合金半固态组织的形成机制。结果表明:在合金的液相线以下开始脉冲放电,二次枝晶臂分离需要较长的时间,一次枝晶臂难以球化;从合金的液相线以上开始脉冲放电,不会析出粗大的枝晶,二次枝晶臂分离比较容易。脉冲电流降低了半固态合金的冷却速度,同时造成了合金熔体强烈的温度起伏;随着脉冲电压的增加,半固态合金的冷却速度逐渐减小,熔体的瞬时平均温升逐渐增加。初始形核率的提高和二次枝晶臂的根部熔断是低压脉冲电流下球状或颗粒状初生α-Mg形成的重要机制。     

层流作用下随机取向多晶粒生长的相场法模拟(英文)

为了更客观地再现强迫层流对多晶粒凝固过程的影响,自行设计了随机格子法以解决多个枝晶择优生长方向随机分布问题。以高纯丁二腈(SCN)为例,采用耦合流场的单相场模型研究强迫层流对多晶粒非等温生长过程的影响。结果表明:随机格子法可以更合理地处理枝晶择优取向随机分布问题,计算效率较高。当固相率较低时,熔体质点绕过枝晶流向下游侧,两枝晶臂之间的熔体流动速度值变大;在凝固计算时间小于1800Δt时,各个枝晶自由生长,上游侧枝晶臂均比下游侧枝晶臂发达;并且,熔体流入速度越快,固相率越高。当固相率较高时,多个枝晶臂相互交织,仅有未被枝晶包裹的残留熔体可以流动;同时,固相率趋于与熔体无流动时的固相率相同。     

熔体流动方向对Fe-C合金枝晶生长的影响

采用熔体流动的相场模型,模拟了Fe-C合金等温凝固中的枝晶生长过程,研究了流动方向对枝晶生长行为的影响。结果表明:在流动方向与晶粒优先生长方向平行时,晶粒第一、二象限的主枝和侧枝粗大,第三、四象限的主枝和侧枝细小。随着流动方向与枝晶优先生长[100]方向夹角θ0的增加,晶粒第一、四象限的侧枝数量增加且生长迅速,第二、三象限的侧枝退化;同时,[100]方向枝晶臂长度减小,溶质浓度降低,[-100]方向枝晶臂长度增加,溶质浓度先减小后增加。     

倾斜冷却剪切流变参数对半固态AlSi9Mg合金组织的影响

利用自制的实验装置研究倾斜式冷却剪切流变技术制备半固态AlSi9Mg合金.结果表明:合金熔体在倾斜冷却板表面非均匀形核并受到重力和振动力的剪切作用,初生α(Al)逐渐从枝晶网络演化为细小的球状或粒状晶;控制浇注温度在600℃、倾斜板长度在600 mm、振动频率在50 Hz时可以获得组织良好的半固态合金熔体,合金熔体中初生α(Al)的平均晶粒尺寸为50μm,形状因子为0.71;机械振动能显著细化AlSi9Mg合金组织,随着振动频率的提高,初生α(Al)明显细化,圆整度也随之提高.     

Effects of Post-weld Heat Treatment on Microstructure,Mechanical Properties and the Role of Weld Reinforcement in 2219 Aluminum Alloy TIG-Welded Joints

In as-welded state, each region of 2219 aluminum alloy TIG-welded joint shows diff erent microstructure and microhardness due to the diff erent welding heat cycles and the resulting evolution of second phases. After the post-weld heat treatment, both the amount and the size of the eutectic structure or θ phases decreased. Correspondingly, both the Cu content in α-Al matrix and the microhardness increased to a similar level in each region of the joint, and the tensile strength of the entire joint was greatly improved. Post-weld heat treatment played the role of solid solution strengthening and aging strengthening. After the post-weld heat treatment, the weld performance became similar to other regions, but weld reinforcements lost their reinforcing eff ect on the weld and their existence was more of an adverse eff ect. The joint without weld reinforcements after the post-weld heat treatment had the optimal tensile properties, and the specimens randomly crack in the weld zone.     

The First Phase of the SRIF Industrialized Base in ＂West Area＂ Has Been Put into Operation

After nearly two years＇ tense construction, the first phase of industrialized base of Shenyang Research Institute of Foundry （SRIF）, located at the Tiexi Casting and Forging Industrial Park in the west of Tiexi District, has now been completed and formally put into operation.     

新型的治疗阿尔茨海默氏症药物(1-二甲基磷酰基-2,2,2-三氯)-乙基-1-醇烟酸醋对体外神经细胞的作用

目的: 观察本实验室合成的一种治疗阿尔茨海默氏症(AD)的药物(1-二甲基磷酰基-2, 2, 2 -三氯)-乙基^-1-醇烟酸醋(NMF),对体外培养的皮层神经细胞活性的影响以及对海人藻酸(KA)所致的神经损伤的保护作用。方法: 采用体外培养皮层神经元的方法,解剖分离 15 d胚胎小鼠皮层神经细胞, 接种于 96孔板,48 h 后加药并培养 72 h,以 MIT 法 观察 NMF 对小鼠皮层神经细胞活性的影响;同时将接种于 24 孔板的细胞预先给予 NMF,d 3 时加或不加KA处理后,以台盼蓝染色鉴别并计数死、活细胞,可得出细胞的存活率。结果: NMF 明显促进胎鼠皮层神经元活性,其中 NMF1、0. 1、10nmol·L^-1促进神经元活性增殖率分别高达 34.7%、37.4%、36. 7%, NMF 明显促进正常胎鼠皮层神经元存活卒,与对照组比较,10nmol·L^-1 NMF 对皮层神经元的存活率分别提高 39.3%、73.5%。 NMF能显著 对抗 KA 所致的神经元损伤,与 KA 损伤组相比, NMF0.1、10、10nmol·L^-1对损伤皮层神经元的保护率分别为 77.30%、80.10%、84.15%。结论: NMF 明 显促进胎鼠皮层神经元的洁性、提高正常皮层神经元,的存活卒,并能有效地保护KA所致的神经元损伤,提示 NMF 是一种很有潜力的治疗 AD 的药物。     

THERMODYNAMICS STUDY ON THE DECOMPOSITION OF CHROMITE WITH KOH

Institute of Process Engineering, Chinese Academy of Sciences, China, has proposed a method for oxidative leaching of chromite with potassium hydroxide. Understanding the mechanism of chromite decomposition, especially in the potassium hydroxide fusion, is important for the optimization of the operating parameters of the oxidative leaching process. A traditional thermodynamic method is proposed and the thermal decomposition and the reaction decomposition during the oxidative leaching of chromite with KOH and oxygen is discussed, which suggests that chromite is mainly destroyed by reactions with KOH and oxygen. Meanwhile, equilibrium of the main reactions of the above process was calculated at different temperatures and oxygen partial pressures. The stable zones of productions, namely, K2CrO4 and Fe2O3, increase with the decrease of temperature, which indicates that higher temperature is not beneficial to thermodynamic reactions. In addition, a comparison of the general alkali methods is carried out, and it is concluded that the KOH leaching process is thermodynamically superior to the conventional chromate production process.     

INFLUENCE OF HEAT TREATMENT ON DAMPING BEHAVIOUR OF THE MAGNESIUM WROUGHT ALLOY AZ61

The effect of isochronal heat treatments for 1h on variation of damping, hardness and microstructural change of the magnesium wrought alloy AZ61 was investigated. Damping and hardness behaviour could be attributed to the evolution of precipitation process. The influence of precipitation on damping behaviour was explained in the framework of the dislocation string model of Granato and Lücke.     

Theoretical Analysis for the Motion and Temperature of Melt Droplets in Spray Degassing Process

The motion of melt droplets in spray degassing process was analyzed theoretically. The height of the treatment tank in spray degassing process could be determined by the results of theoretical calculation of motion of melt droplets. To know whether the melt droplets would solidify during spraying process, the balance temperature of melt droplets was also theoretically analyzed. Then proof experiments for theoretical results about temperature of melt droplets were carried. In comparison, the experimental results were nearly similar to the calculation results.     

Growth Kinetics of Single Inclusion Particle in Molten Melts

On the basis of the single-particle framework, a new theory on inclusion growth in metallurgical melts is developed to study the kinetics of inclusion growth on account of reaction and collision. The studies show that the early growth of inclusion depends on reaction growth and Brawnian motion collision, and where the former is decisive, the late growth depends on turbulence collision and Stokes＇ collision, and where the former is dominant; collision growth is very quick during the smelting process, lessened in the refining process, but nearly negligible in the continuous casting process.     

An Easy Way to Quantify the Adhesion Energy of Nanostructured Cu/X(X=Cr,Ta,Mo,Nb,Zr) Multilayer Films Adherent to Polyimide Substrates

An approach based on film buckling under simple uniaxial tensile testing was utilized in this paper to quantitatively estimate the interfacial energy of the nanostructured multilayer films(NMFs) adherent to flexible substrates. The interfacial energies of polyimide-supported NMFs are determined to be *5.0 J/m2 for Cu/Cr, *4.1 J/m2 for Cu/Ta,*2.8 J/m2 for Cu/Mo, *1.1 J/m2 for Cu/Nb, and *1.2 J/m2 for Cu/Zr NMFs. Furthermore, a linear relationship between the adhesion energy and the interfacial shear strength is clearly demonstrated for the Cu-based NMFs, which is highly indicative of the applicability and reliability of the modified models.     

High-Speed Friction Stir Welding of SiC_p/Al–Mg–Si–Cu Composite

A 17 vol% SiCp/Al–Mg–Si–Cu composite plate with a thickness of 3 mm was successfully friction stir welded(FSWed) at a very high welding speed of 2000 mm/min for the first time. Microstructural observation indicated that the coarsening of the precipitates was greatly inhibited in the heat-affected zone of the FSW joint at high welding speed, due to the significantly reduced peak temperature and duration at high temperature. Therefore, prominent enhancement of the hardness was achieved at the lowest hardness zone of the FSW joint at this high welding speed, which was similar to that of the nugget zone. Furthermore, the ultimate tensile strength of the joint was as high as 369 MPa, which was much higher than that obtained at low welding speed of 100 mm/min(298 MPa). This study provides an effective method to weld aluminum matrix composite with superior quality and high welding efficiency.     

Three-Dimensional Growth of Coherent Ferrite in Austenite: A Molecular Dynamics Study

Coherent second phase often exhibits anisotropic morphology with specifi c orientations with respect to both the second and the matrix phases. As a key feature of microstructure, the morphology of the coherent particles is essential for understanding the second-phase strengthening eff ect in various industrial alloys. This letter reports anisotropic growth of coherent ferrite from austenite matrix in pure iron based on molecular dynamics simulation. We found that the ferrite grain tends to grow into an elongated plate-like shape, independent of its initial confi guration. The fi nal shape of the ferrite is closely related to the misfi t between the two phases, with the longest direction and the broad facet of the plate being, respectively, consistent with the best matching direction and the best matching plane calculated via the Burgers vector content(BVC) method. The strain energy calculation in the framework of Eshelby's inclusion theory verifi es that the simulated orientation of the coherent ferrite is energetically favorable. It is anticipated that the BVC method will be applicable in analysis of anisotropic growth and morphology of coherent second phase in other phase transformation systems.