For a practical pulse laser beam welding (PLBW) process of metal sheets assembled in butt joint configuration, the precise control of the assembling clearance has been a challenge. The existence of machining burrs and assembly errors will lead to forming severe defects, such as misalignment, welding leakage, and penetrating. In this paper, a pair of Ti6Al4V plates with a 0.2 mm air gap was tested by an improved PLBW process. A three-dimensional multi-phase and multi-physical field coupling model of Ti6Al4V alloy plate with a reserved air gap was established according to the weld profile, and the dynamic behavior of the keyhole and molten pool was simulated. Transient temperature field, velocity field, keyhole size, and liquid bridge connection were calculated by using different welding heat input parameters. The results showed that the weld profile simulated by the CFD model is in good agreement with the experimental results, and the deviation is between 0.68% and 7.95%. After the laser power reaches the peak value, the metal steam eruption weakens and the obvious Marangoni vortex appears in the molten pool. The simulated keyhole is always in three stages, that is, the keyhole appears, and then gradually forms the through-hole. The through hole keeps oscillating, and finally, the keyhole shrinks and disappears when the laser power drops to zero. With the increase of laser peak power, the keyhole shape becomes more curved, indicating that the keyhole oscillation is enhanced. With the increase in welding speed, the stability of the molten pool is improved, and the area of the liquid bridge rises more regularly.
The present paper investigates the tensile behaviour of alloy 718 sheets processed after electron beam welding (EBW). The alloy 718 sheets were pretreated in three conditions: as received, solution and precipitation pretreatments. Metallographic and fractographic examination on the specimens were conducted with optical microscope, scanning and transmission electron microscopes. Experimental results show that cracks propagate through all of the fusion zones during tensile test. The intermetallic laves phase, which precipitates along the fine columnar grain boundary in the fusion zone, offers a preferred crack propagation path, especially for the precipitation pretreated weld. The static ductility of precipitation-treated weld decreases significantly after EBW. This was attributed to high precipitation density of laves phase along the columnar grain boundary. Relatively high tensile strength and ductility of as-received and solution-pretreated welds can be obtained by using two sequential welding passes. The first pass is full penetration welding with high heat input, and the secondary pass uses cosmetic welding to reduce the surface undercut resulted from the first pass.
Bearing capacity and durability of corroded steel bars is strongly deteriorated, and the degradation of mechanical properties versus corrosion ratio is topical. Given the random nature of corrosion process, stochastic method can be used to describe mechanical performance of corroded steel bars. In this paper, to simulate marine tidal zone environment, steel bars corroded by chloride solution under dry-wet cycling are studied experimentally, while mechanical performance deterioration of corroded steel bars is analyzed statistically. The corrosion ratios of specimens are found to increase over time for several phases, while their strength dropped with corrosion ratio. The residual nominal strength to corrosion ratio of steel bars is found to be well fitted with the Gumbel distribution, which parameters are calculated and discussed in detail.
For a practical pulse laser beam welding (PLBW) process of metal sheets assembled in butt joint configuration, the precise control of the assembling clearance has been a challenge. The existence of machining burrs and assembly errors will lead to forming severe defects, such as misalignment, welding leakage, and penetrating. In this paper, a pair of Ti6Al4V plates with a 0.2 mm air gap was tested by an improved PLBW process. A three-dimensional multi-phase and multi-physical field coupling model of Ti6Al4V alloy plate with a reserved air gap was established according to the weld profile, and the dynamic behavior of the keyhole and molten pool was simulated. Transient temperature field, velocity field, keyhole size, and liquid bridge connection were calculated by using different welding heat input parameters. The results showed that the weld profile simulated by the CFD model is in good agreement with the experimental results, and the deviation is between 0.68% and 7.95%. After the laser power reaches the peak value, the metal steam eruption weakens and the obvious Marangoni vortex appears in the molten pool. The simulated keyhole is always in three stages, that is, the keyhole appears, and then gradually forms the through-hole. The through hole keeps oscillating, and finally, the keyhole shrinks and disappears when the laser power drops to zero. With the increase of laser peak power, the keyhole shape becomes more curved, indicating that the keyhole oscillation is enhanced. With the increase in welding speed, the stability of the molten pool is improved, and the area of the liquid bridge rises more regularly.
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