The process of vacuum electron beam welding is characterized by deep-penetration with the action of keyhole effect. The assumption of simple cylindrical physical model of keyhole is reasonable according to the thermal transfer of the keyhole effect during welding. There is an intensive evaporation arises from the front keyhole wall owing to the high energy density of electron beam. Therefore, an analysis model of heat transfer at the interface of vapor phase and front keyhole wall was proposed to the temperature calculation on the basis of heat transfer theory. The evaporation of the primary elements, which are Mg, Al, Zn and Mn in AZ series magnesium alloy, can be analyzed by the model, as well as the influence of keyhole radius varying on the temperature at vapor-solid interface offront keyhole wall. And dimensionless parameters are introduced to analyze the influence of the process condition on the thermal effect. The calculation results show that Mg and Zn are vulnerable to vaporize loss during the vacuum electron beam welding on AZ series magnesium alloy, and the evaporation of Mg occurs earlier than Zn. A longer electron beam acting duration and smaller keyhole size will increase the temperature of the front keyhole wall significantly, which has a considerable influence on the evaporation effect of the elements.
Microstructures, tensile properties and work hardening behavior of friction stir welded (FSWed) AA2219-T62 aluminum alloy (in its one-third bottom slice of a 20 mm thick plate) were evaluated at different strain rates. While the yield strength was lower in the FSWed joint than in the base metal, the ultimate tensile strength of the FSWed joint approached that of the base metal. In particular the FSW resulted in a significant improvement in the ductility of the alloy due to the prevention of premature failure caused by intergranular cracking along the second-phase boundary related to the presence of the network-like grain boundary phase in the base metal. While stage III and IV hardening occurred after yielding in both base metal and FSWed samples, the FSW led to stronger hardening capacity and higher strain hardening exponent and rate due to the enhanced dislocation storage capacity associated with the microstructural change after FSW. The fracture surface of the FSWed joint was mainly characterized by dimples and tearing ridges along with micropores.
In this paper, numerical modeling of inertia friction welding (IFW) for Inconel718 was performed using ABAQUS/Explicit with a 3D finite-element (FE) model and the coupled thermo-mechanical analysis. A new thermal input model has been deduced according to the characteristics of IFW and law of conservation of energy. The evolution of temperature field as well as the deformation pattern of the inertia welded joint has been predicted. It is shown that the interface temperature firstly increases rapidly to about 1100 °C within 3 s and then increases slowly. The energy input rate at the interface during the IFW process is closely related to the rotational speed and friction torque of flywheels. The temperature distribution at the interface is very inhomogeneous especially at the initial stage and finally tends to become uniform with the increase of time. Consequently, the flash start to appear as the interface temperature becomes homogeneous relatively and the plastic flow of metal at the interface happens. The verifying trial was carried out and the predicted temperature was compared with the experimental data measured by means of thermocouples. The shape of flash in simulation result was contrasted with the true shape of specimen under the same welding conditions. It is noted that the simulation results agrees well with the experimental results.
The purpose of this study was to evaluate the influence of heat treatment on the microstructural change and low cycle fatigue (LCF) resistance of an electron beam welded (EBWed) dissimilar joint between Ti-6Al-4V and Ti17 alloys. The aging with solution (STA) had a more significant effect on the microstructure and hardness than aging, compared to the as-welded joint. The post-welded joints in both aging and STA conditions were basically cyclic stable at low strain amplitudes up to 0.6%, while cyclic softening occurred at higher strain amplitudes. The fatigue life in the aging condition was slightly longer than that in the STA condition at the lower strain amplitudes. Fatigue crack initiation occurred from the specimen surface or near-surface defect, and fatigue crack propagation was characterized mainly by the fatigue striations coupled with secondary cracks in both aging and STA conditions.
The temperature evolution in inertia friction welded Inconel 718 joint was measured by means of embedding thermocouples in specimens. The spatial distributions of temperature in the axial and radial directions of weldments were obtained and the varying characteristics of the temperature distributions were analyzed. The results indicate that the heating rate during the inertia welding process decreases gradually. The temperature distribution in the radial direction of weldment is uneven and the temperature rises gradually with the increase of distance from the center. But the relation between the temperature and distance is nonlinear. In the axial direction, the shorter the distance from the initial friction surface is, the bigger the rate of temperature increment becomes and the higher the peak temperature and the temperature gradient are. Meanwhile, the longer the distance from the initial friction surface is, the later the peak temperature appears and the longer the delay time gets. Moreover, the results of microhardness testing in a welded joint prove that the measurement of temperature in this study is reliable.
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