超声波对铝合金熔体的有效细化区域

为了探讨凝固组织的超声细化区域范围,在液相线温度至575℃区间内对铝合金熔体施加超声振动,待铸锭冷却至室温,经腐蚀处理后观察其宏观和微观组织.试验结果表明,在工具杆端面位置处靠近铸锭边缘有一明显的作用区域分界线,分界线两端组织呈现截然不同的特征,端面以下组织均得到了有效的细化,而端面以上组织晶粒粗大,呈枝晶状分布.超声在熔体中产生空化和声流效应,理论计算表明,熔体中的有效空化范围为端面下30mm区域内,超声在熔体中产生的声流效应遍及整个熔体可流动区域,通过声流和空化的双重作用,工具杆端面以下的组织均受到超声的作用,并得到细化.     

超声振幅对激光熔注镁合金凝固组织的研究

采用CA法建立了镁合金晶粒生长模型,研究了超声振动作用下镁合金熔体的晶粒生长。结果表明,随着超声振幅的增大,熔体过冷度呈幂函数增大,熔体在过冷度很小时,基本不形核,达到一定值时,形核率急剧增加。当振幅达到10μm时,超声振动提高的过冷度达到32.23K,镁合金熔体形核率为未施加超声的353倍。超声振动的引入增大了合金熔体的过冷度,提高了熔体形核率,凝固组织平均晶粒尺寸减小,组织分布更均匀。模拟结果与试验结果相符,说明该模拟可以指导超声振动在辅助激光熔注工业生产中的应用。     

纵向超声波辅助微注塑方法

微注塑过程中,聚合物熔体在微小腔体中流动时充模阻力比常规注塑大,这影响了熔体填充效果,同时热量损失的不均衡性和不确定性容易导致注塑精度不高．提出了纵向超声波辅助微注塑方法,并对超声波振动对聚合物熔体的作用机理进行了探讨,分析了超声换能器结构对应力、振幅和响应频率的影响．基于对微注塑过程的模拟结果,开发了纵向超声波辅助微注塑装置．通过在微注塑过程中纵向超声波对熔体的能量作用降低熔体黏度,改善了熔体流动和充填性能．为了验证超声波辅助微注塑的效果,进行了菲涅尔透镜实际注塑实验．实验结果表明,相同的注塑工艺条件下,超声辅助微注塑过程中聚合物熔体的充填性能提高了6．91％．     

杂质元素对镁合金组织与性能的影响及其对应措施

镁及镁合金中杂质元素的含量及作用已受到广泛关注.介绍了镁合金中Fe、Cu、Ni、Si等杂质的存在形式,综述了杂质元素对镁合金显微组织、腐蚀性能、力学性能的影响规律及机制,并叙述了几种提高镁合金纯度常见的方法,包括选用高纯原料、优化熔炼工艺、镁合金熔体纯净化,指出有效降低杂质含量将是未来高性能镁合金材料研究的重要方向.     

镁合金复合细晶强化研究进展

细化镁合金的晶粒可极大改善其综合力学性能,单一的细化方法包括在熔体中施加外力场作用、高压和激冷作用以及大塑性变形,单一细化方法下的材料性能难以满足实际需求,且生产效率低、成本高、质量难以保证.2种及以上细化晶粒方法的结合可以实现镁合金性能的极大提升,通过评述镁合金复合加工方法,包括挤压铸造-固态挤压成形、挤压铸造-正挤压成形、FE-CCAE复合变形工艺、电磁脉冲结合轧制工艺、超声振动-挤压加工等,详细阐述镁合金复合细晶强化工艺的研究进展,为进一步研究和开发更加高效绿色的镁合金晶粒细化复合成形技术提供参考.     

镁合金介质保护熔炼技术及其进展

在分析镁合金极高氧化活性的基础上,介绍了镁合金熔体介质保护性熔炼的几种方法,着重对国外应用比较多、保护效果较好的SF6混合气体保护进行了讨论,并对镁合金介质保护熔炼技术发展趋势进行了展望.     

超声波导入时初始温度对铝-硅合金组织的影响

采用高能超声波对Al-20％Si合金进行处理,控制Al-20％Si合金熔体温度在620～680℃,研究合金组织随超声波导入时熔体初始温度的变化规律。实验表明,随着导入超声波时熔体温度的升高,初晶硅形貌由粗大的板片状逐渐变成细小的颗粒状,超声波处理熔体的温度控制在660℃左右时,初晶硅的组织细小、圆整度高、分布均匀。     

超声振动对7055铝合金组织及力学性能的影响

为改善7055铝合金的凝固组织,在合金凝固过程中施加超声振动.采用光学显微镜观察和室温压缩试验等手段研究了超声振动对7055铝合金凝固组织及力学性能的影响,并对超声细化机理进行了探讨.结果表明:未施加超声时,7055合金中形成粗大枝晶组织;施加超声振动后,可获得细小均匀的非枝晶组织.由于超声振动的空化和声流效应,凝固前对熔体施加超声,产生大量微泡核心,这些微泡核心保留下来而成为形核核心,使凝固组织得到细化;凝固过程中导入超声,枝晶出现断裂,导致了细小均匀组织的形成.此外,超声振动的7055合金铸锭显示了较好的室温压缩性能,压缩屈服强度、抗压强度及其对应的工程应变分别为165、729.2 MPa和34.8%.     

超声振动作用下镁-钢焊缝组织演变及力学性能研究

本文旨在通过引入超声振动辅助,实现镁合金和镀锌钢的可靠连接,扩大镁-钢复合构件应用范围。本文在镁合金与镀锌钢的TIG熔钎焊过程中引入超声波振动,并通过金相显微镜、扫描电镜、硬度计和拉伸机等设备对镁-钢接头微观组织和力学性能进行检测,研究超声波功率对镁合金/镀锌钢接头质量的影响。实验结果表明:超声波振动辅助焊接工艺可以有效改善镁/钢接头的焊缝成形,消除接头熔焊区域的气孔等缺陷。研究表明:在焊接过程中引入1 000 W功率进行超声振动后,接头熔焊区的平均晶粒尺寸由初始的51 μm下降到23.2 μm,晶粒细化效果显著;超声振动辅助焊接工艺改善了接头钎焊区反应层的形态,使钎焊区MgZn反应层厚度更均匀,并可以提高接头熔焊区的显微硬度;当超声波功率为1 000 W时,接头力学性能达到3 735 N,相比未施加超声波振动的接头(3 270 N),力学性能提高了14.2%。超声振动辅助工艺可以有效改善镁/钢焊缝的显微组织,提高接头力学性能,实现镁/钢异种金属的可靠连接。     

超声处理对伍德合金细化及气孔生成的影响

主要研究了超声处理对伍德合金凝固组织及气孔的作用.结果表明,超声处理可以明显细化伍德合金的凝固组织;同时超声处理具有明显的除气效果,随着超声波功率的增强,晶粒尺寸明显减小,除气效果显著.对伍德合金凝固过程的超声处理,起主要作用的是声空化和声流作用.     

Effect of acoustic cavitation on ease of infiltration of molten aluminum alloys into carbon fiber bundles using ultrasonic infiltration method

Continuous M40J carbon fiber reinforced aluminum–magnesium alloy composite wires have been fabricated using ultrasonic infiltration. The infiltration phenomenon is examined from the viewpoint of acoustic cavitation. The ease of infiltration of the molten alloys was found to be proportional to the maximum intensity of the acoustic cavitation. The ease of infiltration and the intensity were enhanced by the addition of surfactant elements into the molten aluminum. Thus, a decrease in surface tension caused an increase in the generation of acoustic cavitation thereby resulting in infiltration. Therefore, the generation of the acoustic cavitation is an infiltration controlling factor during the use of ultrasonic vibration.     

Processing,microstructure and properties of ultrasonically processed in situ MgO–Al2O3–MgAl2O4 dispersed magnesium alloy composites

AZ91 alloy matrix composites are synthesized by in situ reactive formation of hard MgO and Al₂O₃ particles from the addition of magnesium nitrate to the molten alloy. The evolved oxygen from decomposition of magnesium nitrate reacts with molten magnesium to form magnesium oxide and with aluminium to form aluminium oxide. Additionally, these newly formed oxides react with each other to form MgAl₂O₄ spinel. Application of ultrasonic vibrations to the melt increased the uniformity of particle distribution, avoided agglomeration, and decreased porosity in the castings. Ultrasound induced physical phenomena such as cavitation and melt streaming promoted the in situ chemical reactions. Well dispersed, reactively formed hard oxides increased the hardness, ultimate strength, and strain-hardening exponent of the composites. Presence of well-dispersed hard oxide particles and stronger interface resulting from cavitation-enhanced wetting of reactively formed particles in the AZ91 alloy matrix improved the sliding wear resistance of the composites.     

Cast aluminium alloy containing dispersions of TiO2 and ZrO2 particles

Up to 4 wt% of ultrasonically-pretreated titania and zirconia particles (5m average size) were dispersed in Al-11.8 wt% Si-1 wt% Mg alloy castings. The technique employed to prepare the cast composites involved mechanically mixing pretreated oxide particles in aluminium alloy melts in the presence of magnesium, followed by casting the resulting mix in permanent moulds. Pretreatment of the oxide particles consisted of agitating the particles in acetone by ultrasonic vibrations to cause the disintegration of agglomerates and the removal of adsorbed water molecules from the particle surfaces. Infra-red (i.r.) spectroscopy of powders showed desorption of water molecules from oxide surfaces by ultrasonic pretreatment in acetone. Ultrasonic pretreatment of oxide particles before their incorporation into the melt and presence of magnesium in the melt were found to be necessary to disperse TiO₂ and ZrO₂ particles in molten Al. Microscopic studies of the composites indicated dispersed TiO₂ and ZrO₂ particles which exhibited a reaction zone at the periphery of the particles, and microprobe X-ray elemental analysis confirmed preferential segregation of magnesium at the particle-matrix interface. The composites exhibited an increase in hardness as a result of dispersions of titania and zirconia particles, while the tensile-strength values of composites were comparable with that of the base alloy.     

Fabrication of continuous carbon fiber-reinforced aluminum–magnesium alloy composite wires using ultrasonic infiltration method

In order to fabricate continuous carbon fiber-reinforced aluminum alloy matrix composites, various infiltration methods such as gas pressure infiltration, CVD-infiltration, and ultrasonic infiltration methods have been developed. Among these methods, the ultrasonic infiltration method is the simplest. In this study, the effects of ultrasonic power, the diameter of the hole of the horn, fabricating speed, and magnesium content on the ease of infiltration are investigated. As the results, both an ultrasonic power of 200 W and the addition of more than 2.4 mass% Mg are indispensable to infiltrate molten aluminum alloy into a PAN-based M40J carbon fiber bundle, which has 6000 filaments. Contrariwise, the tensile strength and relative strength (ROM ratio) of the obtained composites decreased from 1100 MPa (0.7) at both 2.4 and 4.7 mass% Mg contents to 800 MPa (0.5) at 10 mass% Mg content. This was probably caused by an increase in the content of the Al₃Mg₂ intermetallic compound. Consequently, the addition of magnesium is effective in improving the infiltration; however, it causes the strength of the composites to decrease. It is found that in this process, the optimum magnesium content in aluminum from the viewpoints of ease of infiltration and strength was 4.7 mass%.     

液态模锻材料及其研究进展

液态模锻作为一种精密成型技术应用范围不断扩大,液锻件正在不断替代普通铸件和固态锻件用于各行各业。但液态模锻的材料范围不够明晰,导致铸造合金液态模锻研究与应用很多,而各种变形合金的液态模锻却鲜有报道。如果定义适于液态模锻技术成型的材料统称为液态模锻材料,并用流变充型能力、流变补缩能力以及开裂敏感性定量表征液锻材料的工艺性能,则各种合金钢、球墨铸铁、铝合金、镁合金、锌合金、铜合金、生物材料及金属基复合材料都属于液锻材料,且都具有较好的液锻工艺性能。目前只有液锻铝合金、液锻镁合金、液锻锌合金和一些液锻合金钢研究应用活跃,并取得了工业应用。建议今后加强液锻材料的工艺性能预报、变形合金特别是宽结晶温度范围合金的液态模锻以及金属基复合材料的研究开发。     

Kinetic study on the surface oxidation of the molten Mg-9Al-0.5Zn-0.3Be alloy

Be addition make the oxide film formed on the molten magnesium alloy denser and tougher, thus the burning of the Mg during melting was suppressed. AES was employed to study the composition of the oxide film growing on the surface of the molten Mg-9Al-0.5Zn-0.3Be alloy. It was suggested that the surface oxide film could be divided to two layers: the outer MgO layer and the inner mixed layer consisting of MgO and BeO. Both experimental results and theory analysis indicated that the outer layer grew under parabolic law and the thickness almost kept unchanged during the steady growing state for the inner layer.     

Effects of various parameters on ultrasonic separation of inclusions from magnesium alloy melt

The acoustic radiation force generated by ultrasonic standing wave in the flow media can make solid particles suspending in the liquid agglomerate at the nodal planes of the waves and then realize their separation, which is also known as ultrasonic agglomeration in chemical industry. In this paper, ultrasonic waves were employed to promote and accelerate the separation of inclusions from magnesium alloy melt, and the effect of acoustic radiation forces on oxide inclusions removal from magnesium alloy melts were studied by numerical calculation. The agglomeration behavior of the inclusions was also obtained by solving the equations of motion for inclusions. Finally, parametric studies, usually very helpful for continued optimization and design efforts, were carried out to evaluate the effects of various parameters such as ultrasonic power, ultrasonic treating time, particle size and density difference between particle and melt on the inclusions distribution. The results indicate that when a moderate ultrasonic power was applied, most of inclusions could agglomerate at wave nodes in a short time which finally enhanced and accelerated the separation of inclusions from magnesium alloy melt.     

超声辅助制备β-磷酸三钙/Mg-Zn-Ca生物复合材料及性能

在生物Mg合金基体中添加β-磷酸三钙（β-TCP）颗粒可以调控其力学性能及腐蚀降解性能,满足人体不同植入部位的服役需求。本研究在机械搅拌铸造的基础上,采用超声方法对Mg基复合材料的熔体进行辅助处理,制备了β-TCP添加量为1%（质量比）、Zn含量为3%（质量比）、Ca含量为0.2%（质量比）的β-TCP/Mg-Zn-Ca可降解生物复合材料,对超声处理制备的β-TCP/Mg-Zn-Ca复合材料的显微组织、力学性能和腐蚀行为与未超声处理制备的β-TCP/Mg-Zn-Ca复合材料进行了对比研究。结果表明：超声处理可以细化β-TCP/Mg-Zn-Ca复合材料的显微组织,有利于β-TCP复合颗粒的均匀分散;β-TCP/Mg-Zn-Ca复合材料在模拟体液环境下的耐蚀性得到提高;其屈服强度、抗拉强度和伸长率分别为211.54 MPa、334.32 MPa和7.28%,与未超声处理的β-TCP/Mg-Zn-Ca复合材料相比,分别提高了8.44%、4.67%和17.99%。     

Effect of electromagnetic stirring on the microstructures and mechanical properties of magnesium alloy resistance spot weld

This paper investigates the effect of electromagnetic stirring (EMS) on the nugget formation, microstructure, and mechanical properties of magnesium alloy resistance spot weld (RSW). The EMS was induced by an external magnetic field (EMF), which produced by a pair of permanent magnets. The results showed that the EMS drove the molten metal in the nugget to flow clockwise and generated a centrifugal movement, which brought high temperature molten metal from the center of the growing nugget to its edge. Compared with the traditional magnesium alloy RSW, the weld under the EMS effect (EMS-RSW) exhibited larger weld diameter, higher tensile shear force and energy absorption, and finer equiaxed crystal and columnar crystal. The EMS-RSW had a higher hardness ratio of fusion zone to pullout failure location, which indicated that the EMS-RSW was more sensitivity to experience pullout failure. Finally, an empirical failure load formula for magnesium alloy resistance spot weld was developed.     

氧氮化硅/碳化硅材料在镁及AZ91镁合金液中的侵蚀行为

研究了氧氮化硅结合碳化硅(Si2N2O/SiC)材料在纯镁及AZ91镁合金液中的侵蚀行为.扫描电镜显示,金属与氧氮化硅结合碳化硅材料之间有一个很薄的过渡层,基体内部无金属渗入;X射线衍射分析表明,氧氮化硅结合碳化硅材料表面的SiO2与金属液之间发生了反应,形成了腐蚀产物层,SiC和Si2N2O未受到侵蚀;侵蚀动力学表明,当试样表面的SiO2消耗完毕、腐蚀产物在试样表面形成致密的覆盖层以后,试样几乎不再发生明显的侵蚀.