| Large thick-wall components including ships, large-scaled storage tanks, pressure vessels and pipelines urgently required the efficient hybrid laser-gas metal arc welding (GMAW) technology. Additionally, horizontal position welding was a significant join method of the large structure components. The droplet transfer behavior was more complex due to the gravity in horizontal position welding. Meanwhile, the morphology of weld seam was difficult to control. Additionally, the lack of sidewall fusion and incomplete penetration were easily formed in horizontal position welding. Thus, a double-sided hybrid laser-GMAW synchronous welding technology was systematic studied against the application of30mm thick, shipbuilding high-strength steel butt joint in horizontal welding. System researches were developed against the concerned problems of hybrid laser-GMAW welding technology such as the droplet transfer behavior and the influence of heterogeneity of the welded joint on the mechanical properties.Firstly, the effects of laser on the droplet transfer behavior in hybrid laser-continuous and pulse arc welding at flat position were investigated. The results showed that the transfer frequency, diameter and landing location of droplets were affected by the laser in the hybrid laser-continuous arc welding. Additionally, the fluctuation amplitude of the effect in hybrid laser-continuous arc welding was3times compared with that in hybrid laser-pulse arc welding. However, laser mainly affected the landing location of the droplet in hybrid laser-pulse arc welding. Compared with continuous arc welding, droplet transfer was more stable in pulse arc welding which was more suitable for hybrid laser-GMAW welding. On this basis, droplet transfer behavior in hybrid laser-pulse arc horizontal welding was investigated in detail. The results indicated that arc shape was the main controlling factor to achieve stable droplet transfer in hybrid laser-GMAW horizontal welding. In hybrid laser-continuous arc welding and hybrid laser-pulse arc welding, the landing location of the droplet was affected by the direction of the electromagnetic force and the plasma drag force, which were changed as the arc pole area decreased and the arc contracted. The problems such as deviation of arc, landing location of droplet and lack of sidewall fusion in the hybrid laser-GMAW welding of30mm thick, shipbuilding high-strength steel process were solved by using the influence of laser on the arc shape. The deviation of the arc could be effectively suppressed by decreasing the distance between the laser and the wire because the arc could be effectively attracted and compressed when the distance was shorter. Therefore, the electromagnetic force and the plasma drag force promoted the droplet transferred to the weld pool.Secondly, a double-sided hybrid laser-GMAW synchronous horizontal welding of30mm thick, shipbuilding high-strength steel was developed. Root pass welding and filling pass welding processes were optimized and the main controlling factors of the dimensions of welded joint were achieved. The results indicated that a30mm thick, shipbuilding high-strength steel was welded by the novel, high-strength and high-efficient double-sided hybrid laser-GMAW synchronous welding with4passes. Excellentweld surface and welded joints without crack, incomplete penetration, lack of sidewall fusion and porosity defect were achieved. The yield strength, ultimate tensile strength and fatigue crack growth resistance properties of the welded joint were higher than those of the base metal. Additionally, the impact toughness absorbed energy value of the welded joint was57.3J at-50℃. In double-sided hybrid laser-GMAW synchronous welding, root pass welding was the key to guarantee the welding quality. The penetration of the root pass weld was mainly affected by the welding velocity. The width of the middle of the root pass weld was mainly affected by the laser power, while the width of the surface of the root pass weld was mainly affected by the current of the arc. In the root pass welding, the lack of fusion and procity defects could be controled by using high laser power (4.7kW) and low welding velocity (0.6m/min). With those root pass welding parameters, the double-sided weld pool was connected and the penetration was up to18mm. The stable filling pass welding could be achieved by lower laser power (1.9kW) as the arc could be attracted by the laser.In double-sided hybrid laser-GMAW synchronous horizontal welding, not only the dimension but also the microstructure of different zones of the welded joint was heterogeneous because the active area and energy density were different between the laser and arc heat sources. Thus, the mechanical properties of different zones in the welded joint were different. In general, the average penetration of the weld in laser zone was twice of that in arc zone. The average width of the weld in laser zone was only a quarter of that in arc zone. The average grain size of the laser zone was a half of that in arc zone. The percentage of large angle grain boundaries (>15°) in the laser zone was24%higher than that in arc zone. In laser zone of weld, the yield strength, ultimate tensile strength, elongation and impact toughness absorbed energy increased13%,8%,3.1times and78%compared with those of the arc zone at-50℃. Additionally, when stress intensity factor range was80MPa·m1/2, the fatigue crack growth resistance property of laser zone increased17%compared with that of the arc zone.The laser zone in the thick-section, high-strength steel weld by double-sided hybrid laser-GMAW synchronous horizontal welding played a decisive role in improving the mechanical properties of the welded joint. The formations of finer grain and higher percentage of large angle grain boundary (>15°) in the laser zone were the main factors that the static and dynamic mechanical properties of laser zone were higher than those of the arc zone. |
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