Microstructure and Strength of Laser Welds of Sub-micron Particulate-reinforced Aluminum Martix Composite Al2O3p/6061Al

The microstructure of laser welds of sub-micron particulate-reinforced aluminum matrix composite Al2O3p/6061Al and the weldability of the material were studied.Experimental results indicated that because of the huge specific surface area of the reinforcement,the interfacial reaction between the matrix and the reinforcement was restrained intensively at elevated temperature and pulsed laser beam.The main factor affecting the weldability of the composite was the reinforcement segregation in the weld resulting from the push of the liquid/solid interface during the solidification of the molten pool.The laser pulse frequency directly affected the reinforcement segregation and the reinforcement distribution in the weld,so that the weldability of the composite could be improved by increasing the laser pulse frequency.On the bases of this,a satisfactory welded joint of sub-micron particulate-reinforced aluminum matrix composite Al2Op/6061Al was obtained by using appropriate welding parameters.     

Study on behavior of reinforcement in molten pool for submicron composite Al_2O_3p/6061 Al during laser welding

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THE INTERFACIAL BEHAVIORS OF ALUMINUM MATRIX COMPOSITE IN DIFFERENT WELDING METHODS

Non-interlayer liquid phase diffusion welding (China Patent) and laser welding methods for aluminum matrix composite are mainly described in this paper.In the noninterlayer liquid phase diffusion welding,the key processing parameters affecting the strength of joint is welding temperature.When temperature rises beyond solidus temperature, the bonded line vanishes. The strength of joint reaches the maximum and becomes constant when welding temperature is close to liquid phase temperature. Oxide film in the interface is no longer detected by SEM in the welded joint. With this kind of technique, particle reinforced aluminum matrix composite Al2O3p/6061Al is welded successfully, and the joint strength is about 80% of the strength of composite(as-casted).In the laser welding, results indicate that because of the huge specific surface area of the reinforcement, the interracial reaction between the matrix and the reinforcement is restrained intensively at certain laser power and pulsed laser beam.The laser pulse frequency directly affects the reinforcement segregation and the reinforcement distribution in the weld, so that the weldability of the composite could be improved by increasing the laser pulse frequency. The maximum strength of the weld can reach 70% of the strength of the parent.     

MECHANICAL PROPERTIES AND INTERFACIAL STRUCTURES OF ALUMINIUM BORATE WHISKER REINFORCED ALUMINIUM COMPOSITES

Quality 9Al_2O_3-2B_2O_3 whisker reinforced 6061Al or Al composites have beenprepared by technique of squeeze casting.The mechanical properties of the9Al_2O_3·2B_2O_3(w)/6061Al composites could be hardly improved by T6 treatment,owingto cause the remarkable interracial reaction.An observation under high resolution trans-mission electron microscope on interfaces shows that the serious chemical reaction occursand the product is Al_2MgO_4.But no such reaction is found at the interfaces of 9Al_2O_3.2B_2O_3(w)/Al composite.EDS analysis on the interfaces shows that above mentionedinterracial reaction may be resulted from the interracial segregation of Mg atoms in6061Al matrix during sequeeze casting.     

铝基复合材料SiCW/6061Al的激光焊接

采用脉冲激光焊接工艺研究铝基复合材料SiCw/6061Al的焊接性,着重探讨激光输出功率（P）、脉冲频率（f) 对接头性能的影响,借助X射线衍射、扫描电镜、透射电镜等手段分析接头组织。研究发现,焊缝中存在的界面反应物、气孔缺陷,是导致该种材料焊接性显著降低的主要因素。进一步研究表明,在激光焊接条件下铝基复合材料界面反应是不可避免的,反应物沿热流方向生成,具有一定的方向性,激光输出功率是影响SiC-Al界面反应的主要因素,同时提高脉冲频率将对界面反应有一定的抑制作用;焊缝中气孔随激光脉冲频率的增大而减少直至消失。在此基础上,通过制定合理的焊接工艺,获得了成形良好的铝基复合材料激光焊焊缝。     

硼酸铝晶须增强Al复合材料的性能及界面结构

采用挤压铸造工艺制备出复合良好的9Al_2O_3 2B_2O_3晶须增强6061Al合金及纯Al复合材料研究表明,T6处理不能提高9Al_2O_3 2B_2O_3w/6061Al复合材料的力学性能,其原因是T6处理后复合材料中的界面反应明显加重利用透射电子显微术对此复合材料界面的观察与分析认为,界面上存在着严重的化学反应,反应物为Al_2MgO_4将制造态与T6态的界面结构对比发现,正是这种界面化学反应对材料的性能产生不利影响而在9Al_2O_3 2B_2O_3w/纯Al界面上未发现任何化学反应。界面能谱EDS成分分析结果表明,上述界面化学反应是由材料制造过程中基体合金中的Mg在界面上原子偏聚造成的     

铝基复合材料的Al-Cu合金中间层瞬间液相扩散连接

采用Al—Cu合金作为中间层研究了铝基复合材料(Al2O3p／6061Al)瞬间液相扩散连接接头的组织与力学性能。研究结果表明，在Al—Cu／A12O3p／6061Al接头中无明显的增强相偏聚区和增强相贫化区，且接头成分分布较为均匀；在Al—C。合金中间层厚度30μm、连接温度600℃、连接时间30min条件下，接头抗剪强度为130～140MPa,较Cu／A12O3p／6061Al接头抗剪强度提高45％。因此，采用Al—Cu中间层是改善铝基复合材料接头力学性能的有效途径。     

低真空条件下铝基复合材料扩散焊接工艺

以Al2O3p/6061Al铝基复台材科为对象．研究了在低真空条件下的直接扩散焊接和6061Al铝箔作为中间层的扩散焊接工艺。分析了焊接温度．保温时间与不同焊接工艺所得接头微观组织及强度的关系。同时．分析了低真空度和夹具对接头性能的影响。试验结果表明．两种焊接工艺所得接头强度随温度变化的规律以600℃和640℃为界分为三个阶段．并且随保温时间的延长有所提高。在较高的温度下．压力和液态金属的作用促使氧化膜破碎,有利于接头强度的提高。     

亚微米Al2O3颗粒表面稀土改性及其对6061Al复合材料时效行为的影响

采用液相包裹法对亚微米Al2O3颗粒进行稀土表面改性，用挤压铸造法制备表面经稀土改性的Al2O3p／6061Al复合材料．对颗粒表面经稀土改性前后增强6061Al复合材料在不同温度下的时效析出行为进行分析研究．结果表明：改性后的亚微米Al2O3粉体颗粒表面Y2O3包裹均匀，其增强的复合材料在不同时效阶段的硬度值均较改性前有明显提高．且随着时效温度的升高，Mg2Si析出过程加快，时效峰提前，呈现出硬度值变小的趋势，透射电镜观察表明，表面改性颗粒增强的复合材料基体中存在一定量的位错和析出相；而改性前复合材料却呈现出位错和析出相极其稀少的组织特征．分析了改性前后复合材料时效组织形成的原因。     

Parameter optimization for plasma-sprayed Al_2O_(3P)/Al composite coatings on AZ31 magnesium alloy

Al_2O_(3P)/Al composite coatings were prepared on the surface of AZ31 magnesium alloy by plasma spraying technology with mixed powders of Al and Al_2O_3. An orthogonal test containing six factors and five levels was carried out to acquire the optimum technical parameters. Microstructures and properties of the composite coatings were studied. The results show that the coatings consist of Al_2O_3 particulates distributed uniformly and Al matrix, and the interface between the particulate and matrix is continuous, compact and clean. With increasing the mass fraction of Al_2O_3 in the mixed powders, the volume fraction of Al_2O_3 in the coatings increases. The Al_2O_(3P)/Al composite coating with 14% Al_2O_3 volume fraction has more compact microstructure and more satisfactory properties.     

亚微米级Al2O3p/6061Al铝基复合材料扩散焊接工艺

以亚微米级Al2O3p/6061 Al铝基复合材料为对象,研究了直接扩散焊与采用中间层扩散焊两种工艺焊接铝基复合材料的特点、机理,分析了中间层对接头强度的影响规律.结果表明,在铝基复合材料液、固温度区间,存在"临界温度区域",在此温度区域进行直接扩散焊接时,通过液相基体金属的浸润,使得在扩散接合面中增强相-增强相接触转化为增强相-基体-增强相的有机结合,获得高质量焊接接头;进一步研究发现,在扩散接合面上采用合适的基体中间层同样可以将增强相-增强相接触转化为增强相-基体-增强相的有机结合,同时增大"临界温度区域"范围,接头性能更加稳定,接头变形量进一步减小(＜2%).     

冷热循环对颗粒增强铝基复合材料微屈服行为的影响

采用微屈服强度测试、透射电镜和高分辨透射电镜分析,对经过不同冷热循环工艺处理后的颗粒增强铝基复合材料的微屈服行为进行了研究。结果表明,冷热循环次数虽然对颗粒增强铝基复合材料微屈服行为的宏观规律没有本质的影响,但是仍然影响颗粒增强铝基复合材料的微屈服行为。对球形颗粒而言,小应变量下的微屈服强度随冷热循环次数的增加而增高;但对棱形颗粒而言,循环次数的影响较为复杂。研究还表明,冷热循环次数影响颗粒增强铝基复合材料微屈服行为的主要原因是其位错组态和残余应力在不同的循环次数下有明显的不同。     

弥散质点和SiC颗粒复合强化Al基复合材料 Ⅱ．性能和断裂特征

对机械合金化制备的Ａｌ_４Ｃ_３、Ａｌ_２Ｏ_３弥散质点和ＳｉＣ颗粒复合强化Ａｌ基复合材料进行了拉伸试验和断口分析，并测定了弹性模量和热膨胀系数．研究表明，在ＳｉＣ_ｐ／Ａｌ复合材料中引入弥散的Ａｌ_４Ｃ_３和Ａｌ_２Ｏ_３质点可以明显提高复合材料的室温和高温强度，随加入Ｃ含量的增加或Ａｌ粉氧化时间的加长，复合材料的强度提高．在Ａｌ_４Ｃ_３／Ａｌ复合材料的基础上加入ＳｉＣ颗粒可以提高复合材料的弹性模量并进一步降低其热膨胀系数．复合材料断口为大韧窝加细小韧窝的混合断口，随复合材料基体强度的增加，拉伸断口上断裂的ＳｉＣ颗粒数量增多．     

DISPERSOID AND SiC PARTICULATE STRENGTHENED Al COMPOSITES Ⅱ. PROPERTIES AND FRACTURE BEHAVIOUR

对机械合金化制备的Ａｌ_４Ｃ_３、Ａｌ_２Ｏ_３弥散质点和ＳｉＣ颗粒复合强化Ａｌ基复合材料进行了拉伸试验和断口分析，并测定了弹性模量和热膨胀系数．研究表明，在ＳｉＣ_ｐ／Ａｌ复合材料中引入弥散的Ａｌ_４Ｃ_３和Ａｌ_２Ｏ_３质点可以明显提高复合材料的室温和高温强度，随加入Ｃ含量的增加或Ａｌ粉氧化时间的加长，复合材料的强度提高．在Ａｌ_４Ｃ_３／Ａｌ复合材料的基础上加入ＳｉＣ颗粒可以提高复合材料的弹性模量并进一步降低其热膨胀系数．复合材料断口为大韧窝加细小韧窝的混合断口，随复合材料基体强度的增加，拉伸断口上断裂的ＳｉＣ颗粒数量增多．     

Structural Evolution During Mechanical Milling of Bimodal-Sized Al_2O_3 Particles Reinforced Aluminum Matrix Composite

Hybrid aluminum matrix composite powders reinforced with bimodal-sized Al_2O_3 particles were synthesized by mechanical milling. Two different approaches were investigated for the addition of submicron-and nano-sized Al_2O_3 particles to the aluminum powders. It was observed that the simultaneous addition of bimodal-sized Al_2O_3 particles to the aluminum powders resulted in an equiaxed morphology of the composite powders and the average particle size stabilized after 5 h of milling, indicating that the presence of bimodal-sized particles has greater effect on accelerating milling process as compared to nano-sized particles; the grain size of the aluminum matrix in composite powders was reduced to under 40 nm, approximate to the value obtained in the separate addition case, while a lower rate of refining was observed due to hindrance of submicron-sized particles on the interactions between nano-sized particles and the aluminum matrix.     

Al2O3(p)/ZA35锌基复合材料的制备及其磨擦性能

利用Al2(SO4)3分解, 在铝熔体中原位生成Al2O3颗粒.实验结果表明: 采用石墨坩埚、电磁搅拌和铝熔体中加入镁的工艺流程, 可实现Al2O3颗粒和铝熔体的有效复合, 进而制备出Al2O3(p)/ZA35锌基复合材料; 与基体合金ZA35相比, 复合材料的耐磨减摩性能有了明显的提高.     

原位合成(Al_2O_3+Al_3Ti)_P/Al复合材料的制备研究

通过对Al-TiO_2-SiO_2体系混合粉末固-液原位合成制备出了(Al_2O_3+Al_3Ti)_P/Al复合材料.利用X射线衍射仪、扫描电镜等方法观察分析了其物相和显微组织形貌.结果表明:原位反应制备的(Al_2O_3+Al_3Ti)_P/Al复合材料,金属间化合物增强相Al_3Ti均匀分布于基体,陶瓷相Al_2O_3颗粒非常细小,弥散分布于基体中,使材料的硬度等性能得到提高.     

纳米Al2O3P/6061铝基复合材料时效硬化特性的研究

探讨了不同纳米氧化铝颗粒含量、不同时效温度对纳米Al2O3P／6061铝基复合材料时效硬化行为的影响，结果发现，因强化相颗粒与铝合金基体的热膨胀系数差异．提供了析出物形成与成长的驱动力，导致其峰时效时间随强化相颗粒含量的增加及时效温度的升高而缩短，但其峰时效硬度会因时效温度提高使得析出物过度成长而随之降低。复合材料因受强化相与基体材料热膨胀系数的差异、强化相造成的铝合金晶粒细化以及强化相颗粒分散强化等三项因素影响，其硬度值随强化相颗粒增加而提高。     

Al_2O_3颗粒对LiTaO_3压电陶瓷增强增韧机制的探讨

采用氮气保护热压烧结工艺制备Al_2O_3/LiTaO_3(简称ALT)陶瓷基复合材料,研究了Al_2O_3颗粒对LiTaO_3压电陶瓷增强增韧的机制.结果表明,ALT陶瓷复合材料的相对密度比烧结纯LiTaO_3陶瓷的高得多,且其各项力学性能均有明显的提高;Al_2O_3的加入起到烧结助剂的作用;Al_2O_3第二相加入后对LiTaO_3压电陶瓷起到弥散强化作用,其增韧机理为ALT复合材料中残余应力场和裂纹偏转增韧.     

Improvement of the matrix and the interface quality of a Cu/Al composite by the MARB process

The matrix accumulative roll bonding technology （MARB） can improve the matrix performance of metal composite and strengthen the bonding quality of the interface./n this research, for the fwst time, the technology of MARB was proposed. A sound Cu/AI bonding composite was obtained using the MARB process and the bonding characteristic of the interface was studied using scanning electricity microscope （SEM） and energy-dispersive spectroscopy （EDS）. The result indicated that accumulation cycles and diffusion annealing temperature were the most important factors for fabricating a Cu/AI composite material. The substrate aluminum was strengthened by MARB, and a high quality Cu/AI composite with sound interface was obtained as well.