The effects of purge gases on the hydrogen content and mechanical properties of spray-degassed Al

Spray degassing was used to remove hydrogen dissolved in aluminum melt. In order to investigate the effects of different purge gases on aluminum melt during spray degassing, different kinds of purge gases were used in experiments. The results show that, as a purge gas in the process of spray degassing, nitrogen leads in increasing the hydrogen content and inclusion content of the aluminum melt. The mechanical properties of the specimens are very poor.     

电弧喷涂锌合金液滴飞行过程数值分析

运用流体力学,传热学以及相变等理论,建立数学模型描述金属液滴与气流的相互作用,计算了金属液滴的飞行速度和温度衰减过程,结果表明,金属液滴飞行速度,温度以及凝固程度是金属液滴直径,飞行距离的函数,金属射流中固态金属颗粒比例是金属射流中金属液滴质量分布的函数,飞行距离600mm以内,固态,半固态金属颗粒所占比较不超过2％。     

Modeling of heat flow and solidification during atomization and spray deposition processing

A mathematical model of the spray deposition process, based on heat flow analysis during solidification of droplets, as well as that of the spray deposit, is presented. The heat flow during cooling of droplets is analyzed in five distinct stages. A one-dimensional heat transfer model, using a finite difference method, is used to calculate the temperature of the deposit. The results indicate that the cooling rate of a wide size range of droplets of Al-4.5 Cu alloy in the spray varies from 10³–10⁵°C s⁻¹ in contrast to a slow cooling rate of 1–10°C s⁻¹ of the spray deposit. The spray enthalpy on the deposition surface increases linearly with the melt superheat. In contrast, the atomization gas pressure does not have a significant influence on the enthalpy of the spray in this process. The cooling rate of the deposits predicted from the model compares well with those obtained by the measurements.     

雾化工艺对Al-Si合金液滴凝固组织的影响

将雾化合金液滴的传热与运动方程相耦合,对合金的冷却过程进行研究,探讨液滴尺寸、气体初始速度、熔体过热度等参数对合金冷却过程及粉末微观组织的影响,并结合A390合金进行了计算。结果表明,随着液滴尺寸减小,所获得的冷却速度及过冷度增大;当液滴尺寸足够小时,液滴温度的变化趋势及合金液滴的组织将发生突变;增加雾化气体的初始速度,降低熔体过热度,可以抑制初生相的析出,有利于细化合金的组织。     

快速凝固耐热铝合金粉末脱气研究

描述了ＦＶＳ０８１２合金粉末压坯在整个脱气过程中温度—脱气量关系，得出７００Ｋ左右为该合金最佳脱气温度。借助Ｘ射线光电子能谱（ＸＰＳ）对比分析压坯在真空加热除气与空气中加热后粉末表面氧化膜微观结构的不同，发现脱气者较未脱气者氧化膜薄３０％以上，Ｆｅ、Ｖ等元素只分布在氧化膜内层。     

喷射沉积过程中半固态流变组织演变

分析了喷射沉积过程中半固态流变组织演变过程,提出喷射沉积合金细小的等轴晶的凝固组织是飞行阶段快速冷却和沉积阶段沉积体表面糊状凝固层中半固态流变组织演变的结果,沉积体凝固过程是一种微米级流变铸造过程:不同大小、不同状态、不同温度、不同的运动速度的雾滴以高速高频的雾滴撞击沉积体表面,产生足够的剪切应力和剪切速率,使沉积体半固态糊状凝固层具有流变特性,飞行阶段形成快速凝固组织在沉积阶段沉积体表面糊状凝固层中发生变温粗化,最终形成细小的等轴晶。     

一种新的利用落管实验分析微重力效应方法的探讨

通过对金属液滴在落管中下落过程中热量散失及重力水平的计算,讨论了落管在微重力材料研究上的局限性.为了克服落管材料凝固实验中微重力效应和过冷效应难以区分的问题,选取熔点低、发射率低以及比热较高的Al,Cu合金体系以尽量消除熔滴下落过程中的温度差别,采用硅油快淬的凝固方式对比研究了熔滴在落管中下落前后的微观组织.结果表明,这种实验方式可有效突出微重力效应对合金凝固过程的影响,一定程度上拓展了落管在材料研究上的范围.     

铝合金熔体处理及炉料处理的若干问题—铝合金熔体处理部分

系统地介绍了铝液除气、除渣的基本公式，从理论上阐明了诸多工艺参数在除气、除过程中的作用，重点突出了旋转喷吹工艺、泡沫陶瓷过滤及等离子体氩流净化工艺。关于铝合金的变质，主要介绍了三大类变质中的两类，第一类变质介绍了AlTiB的变质效果与其熔制方法有关，第二类变质介绍了锶的多种加入方法及变质效果。炉料处理部分涉及了炉料的遗传性及熔体的除铁处理。     

电弧喷涂层温度场数值模拟

详细介绍了电弧喷涂层沉积过程中三维温度场有限元模拟技术 ,采用有限元分析软件计算了不同工艺、不同时刻以及不同位置涂层内的温度场 ,在建立传热模型过程中考虑了金属液滴束向涂层的传热与传质以及涂层向系统外的热量散失。采用在厚度方向以微小层叠加来模拟涂层的增厚 ,以此为基础构造涂层有限元计算几何模型 ,逐层激活层单元参与计算过程 ,实现移动边界以充分模拟真实的喷涂沉积过程。以实验验证计算结果 ,并详细讨论了喷涂沉积速率、界面传热系数以及间歇喷涂对涂层温度场的影响     

Effect of spray particle trajectory on the measurement signal of particle parameters based on thermal radiation

The influences of the dimensions of optical components and the trajectories of spray particles on the variations of the waveforms of the radiation signals from the spray particles were studied both theoretically and experimentally for correct simultaneous measurement of the particle parameters including particle velocity, surface temperature, size, and spatial distribution. Two types of filtering masks, including single-windowed and dual-windowed, were used as models in the current study. The evolution of the radiation pulse from a moving thermal spray particle was simulated through the change of the projected area of the particle image spot on the filtering mask window. The experimental detection of the thermal radiation pulses was performed for the high velocity oxygen fuel (HVOF) process using an optoelectronic measurement system. The theoretical simulation clearly showed that the characteristic waveforms of the thermal radiation signals from the spray particles are varied with the distance and orientation of the trajectories of thermal spray particles with respect to the ideal image plane of the filtering window plane. The typical variations of the characteristic waveforms obtained theoretically have been observed experimentally with HVOF spraying. The waveforms expected theoretically were correlated well with those observed experimentally. The characteristic waveforms of the radiation signals from the spray particles in a trapezoid shape with a saturated top platform contain the information for spray particle parameters including velocity, surface temperature, size, and spatial distribution. With the dual-windowed filtering mask, the particle velocity can be correctly measured with the bi-peak radiation signal in triangle-like shape, and the surface temperature may be estimated reasonably. However, the particle size cannot be estimated correctly. It was revealed that the characteristics of the waveforms were remarkably influenced by the image spot size. Therefore, the expansion of the image spot based on the relation between the image spot size of an in-flight particle and optical lens parameters obtained optically was discussed. The influence of the image spot size on the waveform characteristics was examined.     

垂直布里奇曼法CdMnTe晶体生长过程的数值模拟与实验研究

为经济高效获得Cd_1-xMn_xTe晶体垂直布里奇曼法(vertical Bridgman method,VBM)生长条件,基于有限元软件建立二维有限体积数值模型,模拟了VBM生长Cd_1-xMn_xTe的晶体过程;探究坩埚内部熔体的传热、流动以及生长界面变化情况,分析5、10和15 K/cm 3种不同温度梯度条件对固液界面的影响。结果表明,晶体生长初期,固液界面径向流速差较大,从而使生长界面略凹向晶体;随着晶体生长的进行,固液界面逐渐平缓,开始有利于良好晶体的生长;在生长中后期,固液界面变为凸面,随着温度梯度的增大,可以更好地抑制对流,有利于获得高质量晶体。在模拟结果的基础上,调整不同阶段坩埚下降速度,进行Cd_0.9Mn_0.1Te晶体的制备,成功地生长出质量良好的Cd_0.9Mn_0.1Te晶体。     

Degassing effect of ultrasonic vibration in molten melt and semi-solid slurry of Al-Si alloys

In the process of semi-solid slurry preparation with direct ultrasonic vibration (UV) by dipping the horn into the melt, one of the questions is whether the gas content in the melt would be increased or not by the cavitation effect of ultrasonic vibration. By application of quantitative gas content measurement technique, this paper investigated the effect of the ultrasonic vibration on the gas content of both the melt and the semi-solid slurry of Al-Si alloys, and the variations of the gas contents in two kinds of aluminum alloys, i.e., A356 alloy and Al-20Si-2Cu-1Ni-0.6RE alloy (Al-20Si for short). The results show that ultrasonic vibration has an obvious degassing effect on the molten melt, especially on the semi-solid slurry of Al-Si alloy which is below the liquidus temperature by less than 20 ℃. The ultrasonic degassing efficiency of the A356 alloy decreases with the reduction of the initial gas content in the melt, and it is nearly unchanged for the Al-20Si alloy. The gas content of both alloys decreases when the ultrasonic vibration time is increased. The best vibration time for Al-20Si alloy at the liquid temperature of 710 ℃ and semi-solid temperature of 680 ℃ is 60 s and 90 s, respectively; and the degassing efficiency is 48% and 35%, respectively. The mechanism of ultrasonic degassing effect is discussed.     

等离子体喷涂中颗粒加热过程数值模拟

目的研究颗粒在等离子体喷涂中的加热过程及影响因素。方法使用Fluent软件对处于等离子射流中颗粒的加热过程与状态进行求解计算,根据计算结果分析了喷距、颗粒直径与颗粒材料对颗粒加热状况与内部温度梯度的影响。结果对于不同的喷距,在颗粒升温过程中,颗粒表面温度高于中心温度;在颗粒降温过程中,颗粒表面温度低于中心温度,并且降温过程中的表面-中心温差远小于升温过程中的表面-中心温差。在颗粒升温过程中,其内部存在不同的加热阶段。对于不同的直径,虽然大颗粒比小颗粒能进入射流中心更深的位置,但小颗粒的加热效果更好。表面-中心温差随着颗粒直径的增大而增大,三种不同直径的颗粒的表面-中心温差变化曲线都表现出相似的趋势。对于不同材料的颗粒,热导率越低的颗粒,其表面-中心温差越高,越难以完全熔化。结论喷距、颗粒直径与颗粒材料对颗粒加热状况和内部温度梯度有很大的影响,该模拟结果能为分析颗粒与等离子体之间的传热提供参考。     

Remelting and bonding of deposited aluminum alloy droplets under different droplet and substrate temperatures in metal droplet deposition manufacture

Micro-void and cold lap are the most common defects of 3D components in aluminum alloy droplet deposition manufacture, which have been found to be associated with the poor remelting and metallurgical bonding between droplets under inappropriate droplet and substrate temperatures. To address this problem, the appropriate temperature condition for achieving good metallurgical bonding between droplets was analyzed and the relationships among surface temperature (T_surf), substrate temperature (T_b), droplets temperature (T_drop), droplets deposition frequency (f) and height of deposition layer (h) were estiblished by one-dimensional (1D) heat transfer analytical model. On this basis, a three-dimensional (3D) transient finite element mode was developed to simulate the thermal behavior during metal droplet deposition component using element birth and death technology. The distribution and variation of surface temperature of previously deposited droplets (T_surf) were predicted and analyzed under different process parameters in fabricating aluminum alloy 3D components. And then, a series of deposition experiments were conducted with different droplet temperatures (T_drop) and substrate temperatures (T_b). The experimental results show that the good remelting and metallurgical bonding between droplets were obtained with the appropriate combination of T_drop (700 °C) and T_b (450 °C). The micro-void and cold laps were not observed in the interior of formed samples, indicating that experimental results basically agree with the theoretical analysis and simulation results. The work provides a useful theoretical and experimental guide for metal droplets deposition manufacture.     

超声场作用下Mg-3Ca合金除气及细化的工艺研究

对Mg-3Ca合金熔体进行超声处理来研究超声功率、施振时间和施振温度对合金除气及凝固组织的影响。结果表明,采用超声波处理技术,可以有效去除Mg-3Ca合金熔体中的气体,从而提高铸锭的致密度。超声除气效果与施振功率、处理时间及处理温度密切相关。当施振功率过小、处理时间过短或过长及处理温度过高或过低均不会有良好的除气效果。熔体处理温度为:700℃,超声功率为150W,处理时间为120s时除气效果最好,除气率可达53.8%。另外,超声波在去除熔体中气体的同时,也使得铸锭的凝固组织变得细小、均匀。粗大的树枝晶不利于气泡的上浮和熔体补缩;而均匀、细小的等轴晶则有利于这一点。     

熔化条件和除气工艺对镁熔体含氢量的影响

利用自行开发的镁合金定量测氢仪研究了熔化条件和除气工艺对镁熔体含氢量的影响。研究结果表明,镁熔体中的含氢量随温度的升高而增大;气体保护下熔炼比熔剂保护的效果好,含氢量较低;随保温时间的延长,气体保护下的镁熔体含氢量几乎没变化,而熔剂保护下的含氢量成小幅上升趋势;采用Ar气除气工艺的效果比C2Cl6除气更有效,镁熔体含氢量更低。     

高速电弧喷涂雾化熔滴的热传输行为

提出了高速电弧喷涂(HVAS)雾化过程熔滴的热传输理论模型,并用一种FeAl合金进行数值分析。结果表明,雾化过程中熔滴的液态冷却速度在105~107K穝-1数量级,预示涂层将具有快速凝固组织特征;熔滴尺寸、雾化气流初始速度、熔滴过热度及喷涂距离对雾化熔滴的热传输行为均有很大的影响;在一定范围内增大雾化气流压力,增大熔滴过热度,缩短喷涂距离,可以有效地改善高速电弧喷涂层的性能。     

用GA-BP算法研究超音速电弧喷涂JCW-S-AM涂层显微硬度与工艺参数间的关系

采用超音速电弧喷涂设备在不同工艺参数条件下制备JCW-S-AM涂层,利用显微硬度计测定各种涂层的显微硬度.根据测试结果,运用GA-BP算法构建涂层显微硬度与喷涂电压、喷涂电流的关系模型并进行工艺参数优化.研究结果表明:喷涂电压和喷涂电流对涂层显微硬度均有影响,呈现非线性规律,并且电压和电流之间存在交互作用;通过遗传算法优化,获得的最佳喷涂工艺参数为:喷涂电压29V,电流200A.此时JCW-S-AM涂层显微硬度最大.     

碳化硅颗粒增强铝基复合材料的重熔和铸造工艺特征

介绍了SiC颗粒增强铸造铝基复合材料的铸锭重熔、除气和铸造过程的特征。由于颗粒的存在 ,这些工艺过程和普通铝合金有一定的差异。在铸锭重熔时 ,需要控制熔炼温度和对熔体施加搅拌 ,以防止颗粒反应和下沉。普通铝合金采用的熔盐和气体除气工艺不适合于复合熔体的除气精炼 ,而真空除气具有很好的效果。复合熔体具有高的粘度 ,流动性较差 ,在大气自由重力浇注时容易卷入气体而导致铸件气孔缺陷。为了防止铸件缺陷的形成 ,复合材料在大气自由重力浇注下的浇注系统需要设计集气、集渣冒口和阻流口等特殊组元。真空差压浇注工艺大大简化了浇注系统 ,降低了材料消耗 ,同时消除了大气自由重力浇注时容易产生的铸造缺陷。通过该工艺可获得形状复杂、表面光洁、尺寸精确的铝基复合材料精密铸件     

冷坩埚连续熔铸与定向凝固Ti6A14V合金的温度场计算

为有效利用冷坩埚，更优控制工艺参数，获得冶金质量良好的铸棒，本文对冷坩埚连续熔铸与定向凝固Ti6A14V温度场进行计算。根据电磁场的感应加热形成上下料棒、电磁压力形成驼峰的情况确定边界条件；采用抛物线逼近确定驼峰形状；对运动单元所处位置的识别实现连铸过程。对功率52kW、速度为3mm／min的条件下进行计算。结果表明，料棒在45s时开始熔化，在70s时形成驼峰，然后熔体获得一定的过热度，形成凝壳，在115s熔体达到最高温度；抽拉过程中上送料能完全熔化，温度场基本稳定，凝固界面的形状和位置基本不变，凝固界面的形状为中间平直、两端上翘，传热基本以轴向传热为主。相同条件下进行实验，实验结果与计算结果相符合，从而证明计算程序在计算冷坩埚连续熔铸与定向凝固温度场是有效的。