Preparation of Ni-CNT composite coatings on aluminum substrate and its friction and wear behavior

Nickel-carbon nanotube(CNT) composite coatings with a Zn-Ni interlayer were prepared by electrodeposition technique on aluminum substrate. The effects of CNT concentration in plating bath on the volume fraction of CNTs in the deposits and the coating growth rate were investigated. The friction and wear behavior of the Ni-CNT composite coatings were examined using a pitt-on-disk wear tester under dry sliding eonditions at a sliding speed of 0.062 3 m/s and load range from 12 N to 150 N. Because of the reinforcement of CNTs in the composite coatings, at lower applied loads, the wear resistance was improved with increasing volume fraction of CNTs. Since cracking and peeling occur on the worn surface, the wear rates of composite coatings with high volume fraction of CNTs increase rapidly at higher applied loads. The friction coefficient of the composite coatings decreases with the increasing volume fraction of CNTs due to the reinforcement and self-lubrication of CNTs.     

铝合金搅拌摩擦焊技术研究存在的问题及趋势

搅拌摩擦焊(Friction Stir Welding-FSW)是目前铝、镁、铜及有色金属等轻合金连接的最先进连接技术之一,FSW与传统熔焊相比,在工艺过程、接头性能等方面具有许多优势.在讨论FSW技术特征、工艺特点及应用研究的基础上,对目前国内外有关FSW技术的研究现状、发展趋势及存在问题进行了详细综述,所涉及的问题是在工业化铝合金结构制造领域(如飞机机身结构、高速客车及汽车车体结构等)大规模推广应用FSW技术必须解决的基础性问题;其次讨论基于FSW研究开发的新思路及新工艺,尤其是搅拌摩擦点焊技术(Friction Stir Spot Welding-FSSW)的原理、特点及在汽车车体轻量化开发中的巨大应用前景.     

热处理对2A12铝合金搅拌摩擦焊板件时效成形的影响

为减弱或消除搅拌摩擦焊工艺(FSW)对时效成形的不利影响,改善2A12铝合金FSW构件的时效成形后的综合性能,通过设计不同的预热处理和时效成形组合工艺,试验研究热处理对2A12铝合金FSW构件时效成形组织和性能的影响。结果表明,在其他条件相同的情况下,预热处理(退火+固溶处理)可有效改善FSW构件的时效成形性。与单一时效成形过程相比,退火+固溶+时效成形组合工艺下,焊接构件的回弹率降低,抗拉强度和焊缝硬度显著提高,且预热处理的存在使得焊缝区域组织得到一定程度的细化和均匀化。经退火+固溶+时效成形的焊件,回弹率可达17.98%;抗拉强度可达394 MPa,为母材的89.5%。     

Optimizing friction stir welding parameters to maximize tensile strength of AA2219 aluminum alloy joints

AA2219 aluminium alloy (Al-Cu-Mn alloy) has gathered wide acceptance in the fabrication of lightweight structures requiring a high strength-to-weight ratio and good corrosion resistance. In contrast to the fusion welding processes that are routinely used for joining structural aluminium alloys, the friction stir welding (FSW) process is an emerging solid state joining process in which the material that is being welded does not melt and recast. This process uses a non-consumable tool to generate frictional heat in the abutting surfaces. The welding parameters such as tool rotational speed, welding speed, axial force etc., and the tool pin profile play a major role in determining the joint strength. An attempt has been made here to develop a mathematical model to predict the tensile strength of friction stir welded AA2219 aluminium alloy by incorporating FSW process parameters. A central composite design with four factors and five levels has been used to minimize the number of experimental conditions. The response surface method (RSM) has been used to develop the model. The developed mathematical model has been optimized using the Hooke and Jeeves search technique to maximize the tensile strength of the friction stir welded AA2219 aluminium alloy joints.     

Developments in investment casting process—A review

Investment casting has been used to manufacture weapons, jewellery and art castings during the ancient civilization. Today, its applications include jewellery/art castings, turbine blades and many more industrial/scientific components. The present paper reviews various investigations made by researchers in different stages of investment casting and highlights their importance. The paper initially highlights the investigations made on pattern wax properties, effects of blending, additives and fillers. Different ways through which pattern properties (like surface finish, dimensional accuracy, etc.) could be enhanced by properly controlling the injection processing parameters are thoroughly discussed. The paper also looks into the investigations made to enhance the strength, surface finish, etc. of ceramic shell for ferrous alloys/non-ferrous alloys as well as superalloys in investment casting. Investigations made on incorporation of nylon fibers and polymer additions confirm that a ceramic shell reinforced with nylon fibers attains additional permeability compared to the one with polymer additions.