Materials Science Forum Vols. 580-582

Abstract: UV curing adhesives have been introduced for bonding various materials at a room temperature. It has the advantage of putting minimum thermal load on the system; however, it is not suitable for precision bonding of micro systems such as micro optical devices because of its high viscosity and poor control of the UV light source. In the present work, a laser-curing bonding process of micro optical devices with a low-viscosity UV polymer adhesive has been developed. A focused Nd:YVO4 laser beam with a spot size of 30 µm with a laser power of 100 ~ 700 mW is used for curing a UV adhesive locally. A thin bonding layer with a thickness of a few hundred nanometers without any thermal effects can be obtained for precision laser bonding for optical fibers. Experimental results are provided and the process characteristics have been discussed. Moreover, potential applications in the field of micro optical systems are introduced as well.

Abstract: Based on the bead on plate test and the effects of heat input on weld penetration, the equivalence between 2 kW CW (Continuous Wave) Nd:YAG laser power and pulsed GMA(Gas Metal Arc) power and the effect of welding speed on their equivalent ratios in welding carbon steel and Al alloy were studied. The studied results show that 9.8 kW pulsed GMA power is needed to reach the same weld penetration depth with 2 kW CW Nd:YAG laser power for welding of low carbon steel at v=1.2 m/min; for Al alloy, it is 3.92 kW pulsed GMA power. The equivalent ratios of 2 kW Nd:YAG laser power and pulsed GMA power are 4.9~6.4 and 1.85~2.1 times at different welding speed for low carbon steel and Al alloy, respectively. But their equivalent ratios have different variations with welding speed; at which the equivalent ratio of low carbon steel increases with welding speed and that of Al alloy decreases. The studied results offer the experimental boundary of heat input for analyzing the effect of Nd:YAG laser power and pulsed GMA power on laser+pulsed GMA hybrid welding process.

Abstract: The Fe-based bulk metallic glass (Fe43Cr16Mo16C15B10) sprayed coating with the thickness about 220%m was successfully deposited on an aluminum alloy (A5052) metal substrate using an HVOF (High Velocity Oxygen Fuel) spraying process. All sprayed coating has still kept the amorphous state after spraying. The Fe-based bulk metallic glass coating shows good adhesion to the aluminum alloy metal substrate, and has a high hardness with HMV 913~1120. It has been found that better properties can be obtained in the sprayed coating by using finer powder.

Abstract: The effects of the plasma spraying parameters on the strength of an Al2O3 coating were investigated by changing the input electrical power to the plasma torch, the spray distance and the Al2O3 powder size as the spraying parameters. The anisotropic feature of the coating strength is also discussed. The strength of the Al2O3 coating in a direction perpendicular to a substrate plane was dominated by the layered structure of Al2O3 splats, and was affected by all the parameters. The strength of the coating in a direction parallel to the substrate plane was not affected by the input electrical power. The strength of the former was lower than that of the latter, in the coating containing many cracks. The anisotropy of the coating strength would be caused by the cracks propagating along the lines of the laminated layer.

Abstract: The welding process, incorporating rapid heating and cooling, generates distortion and residual stress in weldments. Prediction and control of the thermal distortion is particularly important for the design and manufacture of welded thin plate panel. This study aims to develop a thermal elasto-plastic simulation using finite element method to predict distortion, with particular emphasis on buckling deformation generated in a thin metal panel structure welded around hole. In addition, experiments and computations are performed to analyze how hole configuration and the size of the specimen effect distortion.

Abstract: Noncombustible magnesium alloy AMC602 (Mg-6mass%Al-2mass%Ca) extruded sheet of 2.0mm thickness was successfully welded using a fiber laser welding process at welding speed of 10m/min at 3kW laser power. Tensile strength of the welded joint was about 82 to 88% of that of the base metal. Vickers hardness, tensile strength and micro structural properties are also discussed.

Abstract: The optimized condition has been researched, for welding super alloys (Inconel 600, Inconel 625 and Haynes 230), which are used for liquid thruster of an artificial satellite. In the experiment of “bead-on-plate”, these materials are welded using continuous Nd:YAG laser and electron beam. The penetration depth and bead width are measured by optical microscope. The hardness of 1mm depth from welding surface is measured by micro Vickers hardness tester. The tension is tested for measuring the strength of welding part. The tension strength of welding specimen using the Nd:YAG laser is compared with that of the welding specimen using the electron beam.

Abstract: Magnesium alloys are becoming important material for light weight car body, due to their low specific density but high specific strength. However they have a poor weldability, caused by high oxidization tendency and low vapour temperature. In this study, the welding performance of magnesium alloy was investigated for automobile application. The material was rolled magnesium alloy sheet contains 3wt%Al, 1wt%Zn and Mg balance. The effects of filler wire addition was investigated on 2kW Nd:YAG laser welding. For the results, the mechanical properties of welded specimen were similar with base metal in laser welding with and without filler wire. The bridging ability was improved with filler wire without weld properties deterioration on laser welding of magnesium alloy.

Abstract: This work was carried out to obtain sound welds and to select the most suitable binary metal joint among three different dissimilar metal combinations such as Zr-4/Ta, Mo/Ta and Ti/Ta (seal tube/sensor sheath) joints for an instrumented nuclear fuel irradiation test. To do this, the Taguchi experimental method was employed to optimize the experimental data. In addition, metallography, micro-focus x-ray radiography and a hardness test were conducted to examine the welds. From the weld bead appearance, penetration depth and bead width as well as the weld defects standpoint, the Zr-4/Ta joint is suggested for a circumferential joining between a seal tube and a sensor sheath. The optimized welding parameters based on the Zr-4/Ta joint are suggested as well.

Abstract: In general, magnesium metal is not used as uncoated material on account of its corrosion characteristic. This work was done by preparing 99.99% pure magnesium coating films by RF magnetron sputtering onto SPCC substrates [1]. The individual preparation conditions of gas pressures and bias voltages were 1×10-2 ~ 1×10-3 Torr and 0V ~ -300V, respectively. The analysis about crystal orientation, morphology and electrochemical characteristic of Mg thin films was performed by using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), electrochemical impedance spectroscopy (EIS) etc.. It is as a results of experiment that the morphology of the sputtered films changed from a columnar structure to a granular structure when Ar gas pressure increased or bias voltage decreased. Also, the prepared Mg thin film’s morphology did not have defects and pinholes, and the corrosion resistance was improved by the formation of a homogeneous passive layer.