Effect of high density pulse electric current on solidification structure of low temperature melt of A356 alloy

The effect of high density pulse electric current(HDPEC)on the solidification structure of the low temperature melt(LTM)of commercial A356 alloy was investigated.In th experiments.the HDPEC was discharged in the LTM(953K,903K and 873K),By the control experiments,the results showed that the solidification structure of the LTM of A356 alloy is refined apparently when the HDPEC is discharged in low temperature melt.However,the holding time of melt treated has an adverse effect on the soliification structure.The longer the holding time of the melt treated with HDPEC,the coarser the microstructure.With the same discharge voltage.the lower the temperature of LTM,the more obscure the refinement of solidification structure.Finally,the mechanism of microstructure refining by HDPEC was analyzed.     

熔体温度处理对不同成分铝合金凝固组织和性能的影响

运用熔体温度处理工艺 ,研究了A35 6铝合金中Cu ,Fe ,Mg成分的变化对凝固组织及性能的影响。组织观察和性能测试结果表明 ,熔体温度处理工艺能够明显抑制富Cu、富Mg、富Fe等金属间化合物相的析出 ,改善和减小了富Cu、富Mg、富Fe相析出形貌和尺寸 ,显著地提高合金力学性能。用团簇理论分析和解释了有关的实验现象和结果。     

Effect of melt pulse electric current and thermal treatment on A356 alloy

Effects of the melt pulse electric current and thermal treatment on solidification structures of A356 alloy were investigated.In the experiments.the low temperature melt(953K and 903K)treated by pulse electric current was mixed with high temperature metl(1223K).By the control experiments,the results show that the solidification structure of A356 alloy is refined apparently by the pulse electric current together with melt thermal treatment process,and the mechanical properties.especially the elongation ratio of the specimen treated is improved greatly.The structure change of the melt by pulse electric current and melt thermal treatment is the main reason for the refinement of the solidification structure of A356 alloy.     

Separation efficiency of alumina particles in Al melt under high frequency magnetic field

The effects of separation time and magnetic induction intensity on the separation efficiency of alumina particles with diameters varying from 30 to 200 μm in aluminum melt were investigated. The experimental results show that the particle-accumulated layer is formed in the periphery of the solidified specimen when the diameter of the separated molten metal, the magnetic induction intensity and the separation time are 10 mm, 0.04 T and 1 s, respectively. When the separation time is 2 s, the particle-accumulated layer can be observed obviously and the separation efficiency is about 80%. There are few alumina particles in the inner of the solidified specimen when the separation time is 3 s. The separation efficiency higher than 85% can be achieved when the separation time is longer than 3 s. When the magnetic induction intensity is 0.06 T, the visible particle-accumulated layer can be formed in 1 s and the separation efficiency is higher than 95%. The experimental results were compared with the calculated results at last.     

电磁调质A356合金的组织研究

采用低频电磁场对水平连续铸造方法制备A356合金锭坯，通过金相显微镜观察，比较了磁场频率和电流大小对亚共晶区内初生廿灿形貌、晶粒大小的影响，通过扫描电镜分析，确定电磁场对Si在铝中晶内含量的影响。结果表明：与普通电磁铸造比较，低频电磁铸造可以细化晶粒，获得细小的α-Al组织和共晶组织。随着磁场频率降低，晶粒细化更加明显。而电流的增加也可以使晶粒细化，从而获得α-Al非枝晶组织和细小均匀的共晶组织。施加低频电磁场，可以提高Si在铝中的晶内含量，使共晶区域和晶界变窄，且Si的分布更加均匀。     

熔体浇注温度和板倾斜度对倾斜板制备A356铝合金的凝固和显微组织的影响(英文)

采用倾斜板制备A356铝合金半固态浆料。通过倾斜板底部的逆流水冷却使A356合金熔体在流下倾斜板时发生局部凝固,从而导致在板壁上形成连续柱状枝晶。由于强制对流作用,这些树枝晶被折断成等轴和破碎的晶粒,然后被连续冲洗而在斜板出口形成半固态浆料。熔体浇注温度是影响凝固组织的重要条件,而倾斜度为优质半固态浆料提供必要的剪切作用。将得到的浆料在金属模具中凝固以制备理想显微组织的半固态铸造坯料。然后,通过热处理以提高半固态铸造坯料的表面质量。对半固态铸造和热处理后坯料的显微组织进行分析。研究熔体浇注温度(620,625,630和635°C)和板倾斜度(30°,45°,60°和75°)对斜板制备A356铝合金的凝固和显微组织的影响。结果表明:在625°C的熔体浇注温度和60°斜板倾角时,A356铝合金具有细小和球状的晶粒,是最佳的显微组织。     

Effect of pouring temperature on semi-solid slurry of A356 Al alloy prepared by weak electromagnetic stirring

The semi-solid slurry of A356 Al alloy was manufactured by low superheat pouring and weak electromagnetic stirring. The effects of pouring temperature on the slurry manufactured by weak electromagnetic stirring were researched. The results indicate that it is feasible to manufacture the slurry with particle-like primary phases by low superheat pouring and weak electromagnetic stirring, and there is an important effect of the pouring temperature （superheat temperature） on the morphology and the size of primary α -Al in A356 Al alloy. By the action of suitable weak electromagnetic stirring, increasing pouring temperature to put low superheat pouring in practice is capable of obtaining semi-solid slurry of A356 Al alloy with particle-like primary phase. Compared with the samples made only by low superheat pouring without stirring, raising pouting temperature by 15-35℃ above the liquidus temperature under condition of weak electromagnetic stirring can ensure the same grain size and morphology of the primary phase.     

行波磁场连续净化铝合金液实验

采用行波磁场进行了电磁连续净化铝合金液实验,并采用电磁净化金属熔体的轨线模型,对实验中的夹杂物去除率进行了理论预测,结果表明,含夹杂的铝合金液连续液经电磁力作用段时,夹杂物被阻隔,形成电磁过滤效应,而夹杂物聚集区域夹杂物面积分数趋于某一常数,轨线模型预测与实验结果吻合良好。     

Continuous electromagnetic separation of inclusion from aluminum melt using alternating current

A novel scheme about the continuous electromagnetic purification of aluminum melt was put forward based on the utilization of a square separation pipe and a 50 Hz alternating current to produce electromagnetic force. It is experimentally found that with electrical current of 400 A/cm^2, it takes only 10 s to remove 95% inclusion from aluminum melt. Comprehensive numerical simulations were carried out to investigate the dynamics mechanisms behind the process. The results show that the removal of inclusion is attributed to the cooperative effects of electromagnetic buoyancy and the secondary flow induced by the rotational electromagnetic force, and the removal efficient increases with the size of inclusion and the electrical current imposed. Theoretical predictions on the distribution and removal efficiency of inclusion were supported by the experiments.     

Separation of inclusions from aluminum melt using alternating electromagnetic field

Effects of processing variables such as frequency of imposed magnetic field, imposed magnetic flux density, processing time, diameter of inclusions, and value of r1/δ on the electromagnetic separating(EMS) removal efficiency were analyzed theoretically. The higher the frequency, the wider the range of r1/δ will be. Removal efficiency reaches the maximum while r1/δ ranges from 1.5 to 2. And the experimental results on aluminum melt show that higher frequency and magnetic flux density make for higher removal efficiency, matching well with the theoretical results. When f is 15.6kHz, Be is 0.1T, and imposed time is 10s, more than 80% inclusion particles with 6μm diameter can be removed.     

A356合金流动性测试研究

对A356合金流动性能进行测试.结果表明,下列条件测试结果较佳:采用复沟型金属流动测试仪;涂料涂刷厚度0.5mm～0.8mm,两次涂刷;熔体在720℃保温,30min～40min;浇铸温度为690℃;模具保温温度为60℃～80℃.     

熔体处理和双向电磁搅拌复合快速制浆技术

分析了中间合金微细粉末熔体处理工艺和双向电磁搅拌工艺中,Al-5Ti-B合金粉末粒度、粉末加入量、加入温度、静置时间、中间合金加入顺序、单向旋转时间、电源频率、浇注温度和搅拌时间等工艺参数对A356合金半固态浆料的组织和制备效率的影响规律及其原因,开发出适合于铝合金的熔体处理 双向电磁搅拌半固态浆料复合制备技术。结果表明:该技术可在20~25 s内制备出α(Al)的形状因子约为0.85、晶粒尺寸为70~80μm(空冷尺寸)的A356合金半固态浆料。     

Wettability of TiAl alloy melt on ceramic moulds in electromagnetic field

In the electromagnetic field, the wettability between Ti50Al alloy melt and oxide ceramic moulds was studied by the self-designed measuring apparatus. The thermodynamic and kinetic laws and mechanism on wetting were studied systematically. The results show that in the electromagnetic field, the order of contact angles for the molten Ti50AI alloy for the eight oxide materials is θ（Y203） 〉 θ（ZrO2（Y203）） θ〉 0（ZrO2（CaO）） θ〉 0（CaO） ：〉 θ（ZrO2（MgO）） θ〉 0（A1203） θ〉 0（Zircon） ：〉 θ（MgO）. The wetting process of Ti50Al alloy and ceramic moulds includes the nonreactive wetting at the first stage, and the reactive wetting at the final stage. And the higher the ceramic chemical stability, the longer the nonreactive wetting time.     

Rheo-squeeze casting of semi-solid A356 aluminum alloy slurry

The effect of pouring temperature, electromagnetic stirring power and holding process on semi-solid A356 aluminum alloy slurry was investigated, then the slurry was squeeze-cast. The results show that when the pouring temperatures are properly above the liquidus line, for example 630-650 °C, the slurry with spherical primary α(Al) grains can be prepared under the stirring power of 1.27 kW. The slurry is then homogeneously held for a short time, and the primary α(Al) grains are further ripened and distributed evenly in the slurry. The results of the rheo-squeezed casting experiments show that the injection specific pressure has a great effect on the filling ability of the semi-solid A356 aluminum alloy slurry, and the higher the injection specific pressure is, the better the ability for the slurry to fill the mould cavity is. When the injection specific pressure is equal to or above 34 MPa, the whole and compact rheo-squeezed castings can be obtained. The microstructure of the castings indicates that the shape, size and numbers of the primary α(Al) grains in different parts of the castings are highly consistent. After being held at 535 °C for 5 h and then aged at 155 °C for 12 h, the ultimate strength of the rheo-squeezed castings can reach 300-320 MPa, the yield strength 230-255 MPa, and the elongation 11%-15%.     

电磁搅拌对A356合金熔体结构及其凝固行为的影响

对A356合金熔体进行电磁搅拌并浇注至高温铸型中直接制备半固态浆料.利用光学显微镜和扫描电子显微镜研究了过热电磁搅拌对A356合金半固态浆料组织的影响.用Image-Pro Plus图像分析软件对α(Al)初晶的尺寸、圆整度以及Al-Si共晶间距进行分析测算.通过和直接浇注获得的浆料组织进行对比,研究了电磁场对合金熔体结构及其后续凝固行为的影响.结果表明:随着搅拌温度的降低至液相线附近时,电磁场对熔体凝固行为的影响逐渐显著;α(Al)初晶中树枝晶不断减少并逐渐转变蔷薇状晶和非枝晶;水淬后Al-Si共晶组织也由粗大的片层状转变为细小的纤维状和鳞片状结构.这些现象主要归因于电磁场作用下低温熔体中Al、Si的微观偏聚加剧,促进了α(Al)和共晶Si的形核.     

Purification effects of glass flux on A356 melt

In order to remove hydrogen and inclusions from A356 alloy melt, a low melting-point glass flux, JDN-Ⅱ ,was devdoped. The results indicated that JDN-Ⅱ flux has distinct effect of purification and protection on A356 alloy melt. When the dosage of the flux was 3 %, the content of hydrogen in A356 melt was only 2.6 mL/kg at 857℃ and 0.7 mL/kg even at 750℃. In the meantime, the mechanical properties of the alloy increase greatly with the covering of 3% JDN-Ⅱ flux. Compared with no flux, the tensile strength of A356 alloy increases by 9.42% and the donaation increases by 22%.The purification mechanism of JDN-Ⅱ glass flux was discussed too.     

高密度脉冲电流对A356铝合金凝固组织的影响

研究了高密度脉冲电流对A356铝合金凝固组织的影响，实验中对液相线以下溶体的凝固过程在不同阶段进行电脉冲处理。对比实验结果表明：经过电脉冲处理后，A356的合金凝固组织得到明显细化；在同样的电脉冲条件下，凝固组织细化效果与电脉冲放电开始时间有关，凝固过程中放电开始时间越早，凝固组织细化效果越明显；反之，凝固组织细化效果较差；同时，脉冲充电电压越高，凝固组织细化程度越大。定量计算了脉冲电流产生的电磁力并分析了脉冲电流影响凝固组织的作用机制。     

Effect of turbulent flow on electromagnetic elimination with high frequency magnetic field

1 Introduction The application of the electromagnetic body force to separate non-metallic inclusions was proposed by ALEMANY et al[1,2]. And ASAI et al have measured the migration velocity of polystyrene particles in a sodium chloride aqueous solution, in which a DC electric field and DC magnetic field were simultaneously imposed. They found that the direction of migration is opposite to the electromagnetic force and the migration velocity agrees well with the values calculated from the …     

Direct-chilling casting of Mg alloy under electromagnetic and ultrasonic combined field

The effects of low frequency electromagnetic (LFEC) field and ultrasonic (US) field on the microstructures, macrosegregation of alloying elements and the mechanical properties of DC cast AZ80 alloy were studied. The results show that both LFEC and US fields can refine the grains of the billets, which results in the increase in mechanical properties and uniformity of alloying element distribution. The effective refinement takes place on the edge of ingots when LFEC field is applied, while in the center of billets when field US is adopted. Combined the characteristics of LFEC and US fields, a new process for direct-chilling (DC) casting of Mg-electromagnetic-ultrasonic (ECUS) casting is developed, by which the grains are refined significantly and are more uniform in the whole ingots, and the mechanical properties of the ingots are improved.     

铸造A356铝合金的高速热变形行为

文章针对铸造A356铝合金在高速热变形条件下的变形行为开展研究。采用等温热压缩实验,获得了铸态A356合金在温度范围为300℃~450℃,应变速率范围为0.1s-1~50s-1下的流动应力曲线,并对曲线进行了摩擦影响的修正。实验结果表明,铸态A356合金在实验条件范围内的变形机制主要为动态回复,基于动态回复条件下的位错演化理论建立的A356合金的本构方程,可以很好的预测高速热变形时的热变形行为。