Key Engineering Materials Vols. 353-358

Abstract: The ultrasonic welding process of thermoplastic composite with different shapes of energy director (ED) was simulated using finite element model. The results show that the highest temperature zone locates at the tip for the semicircular and triangular ones, and locates at the middle height for the trapezoid one. But it does not locate at the body of ED for the rectangular one. Energy director with different shapes lead to the temperature rising rate at different order of amplitude. The welding amplitude has same influence on the four shapes of ED. The temperature distributing profiles of semicircular, triangular and trapezoid ED keep constant from the initial welding time to that when the highest temperature on joints arrives the temperature of glass transformation (Tg), but the profile for rectangular ED changes greatly.

Abstract: The transient temperature field of Al alloy during electron beam welding (EBW) process was simulated using a three-dimensional finite element method. Different from the most previous models which were based on the assumption that the welding pool was solid and neglected the existence of keyhole by meshing the solid as a whole, a dynamic three-dimensional keyhole was applied in this model. The profile of the keyhole was ellipse and its size was determined before simulation based on the results of experiments. Following the heat source, the pre-defined keyhole moved along the welding line. A three-dimensional complex heat source model, including a modified Gaussian distribution source and a uniform source, was used in this study. The result shows that the shape of the keyhole had a direct effect on the temperature distribution and contribution to the special shape of the welding pool in EBW.

Abstract: In this paper, the weldablity of a low-carbon Cu-bearing age-hardening steel was evaluated using Y-groove cracking evaluation test. The results show that the steel has a low hardenability characteristic and cold-cracking susceptibility. It is also indicated that a crack-free weldment can be obtained during welding of this type of steel even at an ambient temperature as low as -5°C as well as in an absolute humidity lower than 4000Pa without any preheat treatment. A slight preheat treatment can prevent the joint from cracking when welding is carried out at lower ambient temperature or in higher absolute humidity.

Abstract: In this paper, the very rapid thermal cycles imposed on an ultrafine grain steel plate were successfully simulated using a Gleeble™ simulator. The simulated heat affected zone was obtained suitable for Vickers hardness and impact toughness examination of laser weld that originally bear a narrow zone with high hardness gradient. Effect of preheat treatment on the mechanical behavior of laser HAZ was estimated. It was indicated that the simulated HAZ was composed of fine martensitic ferrite laths with average width in 65nm and 175nm in the case of preheat at 200°C and not, respectively. The laths were cramped by retained austenite film within the prior austenite grain with average size of 9.5 and 6.5μm, much less than that of base metal. The impact toughness of HAZ was improved by laser thermal cycle comparing to that of base metal, and there is no obvious brittle-ductile transition under temperatures from -80°C to 20°C. Preheat treatment of steel plate prior to laser welding resulted in an effective reduction of the maximum hardness and alleviation of the hardness gradient in the weld.

Abstract: A Cu brazing sheet has been developed using a Cu-P composite plating method. A Cu-P composite plating layer, which contains 7mass%P, was formed on a Cu plate with a copper sulfate solution including P particles. The melting start temperature of the Cu-P composite layer was determined to be approximately 765°C. Microstructure and joint strength of a brazed joint with the Cu-P composite layer were investigated and compared with those of the joint with a conventional Cu-7P filler foil. As the results of the study, it was clarified that the Cu-P composite layer developed is feasible to use as a brazing material for Cu and Cu alloys.

Abstract: The effect of the mechanical and physical properties of an underfill material on thermal stress relief in a lead-free chip size package (CSP) solder joint has been investigated. Thin sheets of underfill materials for the CSP solder joint were prepared and the mechanical and physical properties of the sheets were investigated. Using these properties, thermal stress relief in an encapsulated CSP lead-free solder joint with the underfill material was examined by a finite element analysis method under thermal cycle conditions in the temperature range from 293K to 398K and 233K.

Abstract: An influence of content of Ni and Ag in a Sn-Ag-Cu-Ni-Ge lead-free solder has been investigated on microstructure and joint strength of the soldered joint under heat exposure conditions. The growth kinetics of the reaction layer formed at the joint interface has been investigated, and the apparent activation energy of the reaction layer growth has been also examined. Moreover, the soldered joints with Sn-Ag and Sn-Ag-Cu solders were prepared and were compared with the joints with the Sn-Ag-Cu-Ni-Ge solders.

Abstract: In our previous study, loosening-fatigue tests under small transverse vibrations had been performed to elucidate bolt behavior and loosening-fatigue mechanism in the long life region. In this study, the influences of bolt property class and the plastic region tightening on loosening-fatigue characteristics under transverse vibration have been investigated. Result shows that bolt property class has little influence on the loosening-fatigue limits under transverse vibration. Result also shows that the transverse loosening-fatigue limit of the bolt which has been tightened to within the plastic region is lower than the transverse loosening-fatigue limit of the bolt that has been tightened to within the elastic region. This result is the opposite of the result of the axial fatigue characteristics of bolted joints.

Abstract: Conventional Friction Stir Welding (FSW) is that weld materials are joint at room temperature by stirring softened materials due to frictional heat of rotating tool. Therefore, high speed and high efficiency would be expected, as pre-heating make weld materials more softened, as well known that yield point goes lower due to heating. In this study, FSW was done to improve welding speed on FSW of aluminum alloy (A5052) for high vacuum vessel for processing of electronics devices. As the result, welding speed was 2.0 times to more than 3.0 at 300 oC comparing with conventional FSW at room temperature, using improved a milling machine with heater.

Abstract: A new sensing method called “smart stress memory patch”, which could estimate the maximum stress, the stress amplitude and the fatigue cyclic number simultaneously using Kaiser effect of Acoustic Emission (AE) and crack length of this patch, was developed. In this study, the crack growth characteristics of this patch was evaluated. Pure copper was used for this patch because its good corrosion resistance, stable crack propagation and so on. Two kinds of samples which were rolled and electrodeposited copper were prepared to investigate the effect of microstructure on crack growth behavior. Fatigue test was performed under constant stress amplitude to evaluate the crack growth behavior using the relationship between stress intensity factor range and crack propagation rate. The scattering in fatigue crack growth was also investigated to obtain the relationship between crack length and the fatigue cyclic number including two-sided 95% confidence interval. The effect of thickness and grain size on the scattering was discussed. Finally, good crack growth behavior was obtained and the fatigue cyclic number could be estimated by this patch.