Papers by Keyword: Al-Cu

Abstract: Conventional friction stir welding of aluminium to copper often results in the formation of deleterious intermetallic compounds. In order to overcome this concern, an innovative procedure consisting of using an aluminium run-on plate is presented. Long continuous aluminium-copper welds, without any defect, were obtained by this procedure. The run-on plate inhibits the formation of intermetallic compounds around the pin by allowing the use of high tool offset, without the formation of discontinuities at the interface. The generation of an aluminium volume around the tool, which detaches very small copper particles from the copper plate, gives rise to stir zones composed of a uniform distribution of copper particles in an aluminium matrix and with a minimal formation of intermetallic compounds. Comparing to the conventional welds, a significant improvement in the mechanical strength was achieved by welding with this non-conventional procedure.

Abstract: Hot tearing is the one of the biggest problems when casting aluminium alloys. Although there has been much research work in this field, it is still not clear what causes hot tearing and how it propagates. Furthermore, the effect of solidified structure on the hot tearing has not been clear. Therefore, this study has been carried out to correlate the solidified structure and hot tearing. Al-2.0 wt% Cu alloy was used for test alloy. To change the solidified structure, some amount of refiner was added to the molten alloy. A permanent mould, which has been developed by us, can form hot tearing intentionally in the center region of a solidified shell. The cross section of a solidified shell was metallographically investigated and solidified structure and hot tearing were characterized. The length of hot tear decreased with increasing the amount of refiner. This may indicate that it is difficult for hot tear with fine equiaxed grains to propagate. In addition to this, the residual liquid around the hot tear was moved to the cracking due to negative pressure and hot tearing was partially healed.

Abstract: The impact welding was performed for several kinds of metal plate couples. The joint interface exhibited a sinusoidal wave form when two metal plates with the same or similar density (e.g. Al/Al, Cu/Cu and Cu/Ni) were impact-welded by high-speed oblique collision. In contrast, as for dissimilar metal plate couples with large density difference such as Al/Cu, an asymmetric wavy interface was obtained. In order to make clear the reason for morphological difference, a computer simulation of the collision behavior was performed using SPH (Smooth Particle Hydrostatic) method. The simulation results revealed that the wave form was controlled by the interaction between the emitted metal jet and metal plate surfaces ahead of the collision point. For Al/Al and Cu/Ni, the emitted metal jet hit each surface alternatively and this resulted in symmetrical wavy interface formation. While, for Al/Cu, the metal jet was emitted to the direction parallel to the Cu plate, and the interaction took place between the metal jet and the Cu plate surface. The metal jet emission and wavy interface formation mechanism were also investigated.

Abstract: Al-Cu joints have been widely used in electronic and heat exchanger industries due to their excellent electrical and thermal conductivity. Meanwhile, the use of Al in the Al-Cu joints can result in lower weight and cost of the final structure. The purpose of the current study is to join Al to Cu by furnace brazing using ultrafine Al-Si powder. To study the microstructure of the join area, the brazing tests were conducted in the range of 590 to 610°C for 5 to 15 minutes under inert atmosphere. The microstructure of Al/Cu joints was studied by scanning electron microscopy (SEM). The elemental analysis was conducted using an energy dispersive spectrometry (EDS) system. Experimental results show that two kinds of intermetallic compounds (IMCs) mainly Cu₃Al₂ and CuAl₂ phases are formed near the interface of copper and in the braze layer region. The bulky prismatic structure which is formed on the side of Al substrate was found to be α-Al+CuAl₂ eutectic.

Abstract: Titanium and aluminum films were deposited on oxygen-free copper substrates by electron beam evaporation method to obtain Al/Cu and Al/Ti/Cu layer composites. Evolution of microstructure and properties of Al/Cu and Al/Ti/Cu thin film during heat treatment processes were investigated by XRD, SEM and electrical properties analysis. The introduce of Ti layer can prevent the formation of Cu-Al intermetallic compounds, and has no obvious influence on the electrical resistivity of Al/Cu thin film, which can be used as a pad in microelectronic package and devices.

Abstract: Texture and microstructure of FSW joined Al and Cu sheets were investigated by means of electron backscatter diffraction (EBSD) technique. The analysis has revealed a strong texture evolution on both sides of the weld interface as well as a very complex microstructure. Grains were found to be fully recrystallized on both sides of the weld and with different average diameters at different specific zones of the weld.

Abstract: In the present study, we report on an image analysis procedure, which enables to extract from synchrotron radiographs the long range solute profiles in the whole sample and in both phases (solid and liquid). This image analysis is based on the measurement of local density differences, and is applied to study the directional solidification of Al - 4wt% Cu alloy, from planar to onset of the initial instability. Dedicated experiments were carried out at the European Synchrotron Radiation Facility (ESRF) in Grenoble (France). In order to validate this analysis the value of a key solidification parameter, namely the partition coefficient, was experimentally determined during the planar solidification, and a very good agreement was found with value found usually in the literature. On a further step, the evolution of the microstructure and solute profile during the initial transient of solidification was analysed in detail.

Abstract: In this work we are interested by the decomposition behaviour after heat treatment at 500°C of nanostructured Al-Cu deposits, prepared by radio frequency (13.56MHz) magnetron sputtered from composite targets. The use of X-ray diffraction leads to the characterization of different structures and the estimation of grain size and dislocation density. The grain size of the films is found to increase with annealing. The dislocation density is observed to exhibit a decrease trend with annealing temperature which leads to a reduction in the concentration of lattice imperfections A specific thermal study of the Al-Cu deposits, by combined thermal analysis (TDA/TG) permit to follow the structural behavior of the deposits with heat treatment. For Al-7.21at%Cu deposit, the exothermic peak convolution may be due to the elimination of micro deformations present in the sample.

Abstract: To investigate the influence of stress on reactive diffusion, a remarkably clear experiment has been designed. Thin film Al/Cu/Al and Cu/Al/Cu triple layers are deposited on curved substrates of 25 nm radius and investigated by atom probe tomography. Due to the specific geometry, the excess volume of the reaction product induces compressive and dilatational stress on opposite sides of the product layer, even in the case of semi-coherent or incoherent interphase boundaries. The resulting stress gradient leads to additional driving force, which accelerates or decelerates the reaction rate in dependence on the stacking sequence of the layer material. By quantitative analysis, the induced level of stress can be quantified from the modified growth rate of the product.

Abstract: The morphology and phase structure of Al/Cu explosive compounded interface were observed by scanning electron microscope, high-resolution transmission electron microscope and X-ray energy spectrometer. The results reveal that the interface of Al/Cu appears wave-like structure, with an average wavelength of 1.0mm and crest height of 0.3mm. Every wave has its front-nest. The wavelike interfaces are composed of microcrystal compound layer, non-crystal and nanocrystal. Several kinds of compounds such as Al9Cul2, Al4Cu9, Al2Cu, η-AlCu, β-AlCu3 and unidentified phase structure were found in Al/Cu interface. There are some bent lattice fringes around the front-nest. The research of microstructure in anchoring area revealed the nature of explosive cladding in metallurgical anchoring.