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Variable polarity plasma arc welding (VPPAW) can be used for the excellent welding of 5A06 aluminum alloy, which is promising for aerospace applications due to its excellent welding performance and small welding deformation. In this paper, the corrosion behavior of the welding specimens was studied by a metallographic microscope, scanning electron microscope, energy dispersive spectrometer, x-ray diffractometer, and electrochemical workstation. The VPPA welded joint metallographic specimens were subjected to salt spray corrosion tests for 24, 54, 84, 114 and 144 h. The results showed that the heat-affected zone (HAZ) is more sensitive to corrosion than the weld metal (WM) and the base metal (BM), which resulted from the existence and distribution of β(Al3Mg2) and Al6(FeMn) phases in welded joints. The corrosion resistance of VPPA welded joints is WM > BM > HAZ. However, salt spray corrosion increased the corrosion sensitivity of the WM. With the increase of salt spray corrosion time, the WM corrosion tendency raised, and the corrosion resistance of WM became lower than the BM. The corrosion rate curve showed an increasing trend at first and then decreased with the increase of corrosion time, and the corrosion rate reached the highest at 84 h. [ABSTRACT FROM AUTHOR]

In this research, the temperature field characteristics and melt flow behaviors of 5A06/6061 aluminum alloy lock-butt joint during the electron beam welding (EBW) process are investigated by numerical simulation involving heat transfer and flow of fluid. The calculated mesh model of the lock-butt joint is established with the computational domain divided into three phases. The rotating Gauss heat source is applied to simulate the electron beam energy loaded on the base metal during the welding process. Immediately, not only the temperature filed distributions on the surface and different sections of the molten pool are analyzed carefully, but the flow behaviors of the liquid metal in the molten pool are studied in detail. The results demonstrate that the asymmetric distribution of the temperature field, keyhole, and molten pool morphology exist constantly during the welding process. Besides, there are asymmetric metal flows on both sides of the molten pool and obvious vortex metal flows near the rear and the surface of the molten pool. The melt flow on the keyhole wall represents diversity including the surrounding, downstream, and upstream flow. Moreover, the corresponding experiment is conducted to verify the accuracy of the established model and the simulation results are in good agreement with the experimental results in this work. [ABSTRACT FROM AUTHOR]

5A06 aluminum alloy bar was brazed by temperature gradient transient liquid phase diffusion welding (TG-TLP). The effects of brazing temperature on the microstructure and the tensile strength of the brazing joints were investigated. Three typical brazing filler alloys (1# Al-20Cu-6Si-2Ni, 2# Al-10Cu-10Si-3Mg-1Ga, and 3# Al-6Cu-10Si-2Mg-10Zn) were prepared by smelting, and TG-TLP diffusion bonding was carried out at different brazing temperatures (550 °C~590 °C). The results show that with the increase in brazing temperature, the oxide films at the brazing junction are easier to be broken and dispersed, but the oxidation extent will also increase. The oxidation products enriched were mainly Al2O3 and SiO2 at the brazing junction. There are different optimal brazing temperatures corresponding to the different filler alloys. For 1#, the optimal temperature is 570 °C; for 2# is 580 °C; for 3# is 580 °C. For 1# brazing joints, the maximum tensile strength was 113 MPa, and for 2# was 122.4 MPa. Under the experimental conditions of this study, the maximum tensile strength of the TG-TLP joint is 147.4 MPa of 3# brazing sample (at 580 °C), which has increased by 30% and 20% compared to 1# and 2# respectively. The nickel-rich phase at the interface (of 1# brazing filler) could form a brittle fracture, which was unfavorable for interface bonding. For TG-TLP brazing of 5A06, the filler alloy with high Al:Cu ratio (12:1 wt.%) needs a sufficient temperature gradient to exert the film-breaking effect, while the filler alloy with low Al:Cu ratio (3.6:1 wt.%) needs to accurately control its brazing temperature to avoid excessive oxidation. There are many research gaps in the influence of brazing material composition and brazing temperature on the microstructure and mechanical properties of 5A06 aluminum alloy TG-TLP joints. The research results can provide a theoretical basis for formulating the TG-TLP brazing specification of 5A06 aluminum alloy. [ABSTRACT FROM AUTHOR]

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In this paper, the numerical simulation of the temperature field and welding angular distortion of a 6mm-thick 5A06 aluminum alloy plate was performed by application of the ABAQUS 2018 finite element analysis software. A 3D thermo-mechanical model of the plate under study with account of heat transfer in the arc motion direction was established. The temperature field distribution and welding-induced angular distortion in the welded structure obtained by the simulation were analyzed to minimize the production cost and improve the production efficiency. By analyzing the magnitude and distribution of residual stresses in the welded structure, selecting a reasonable welding process, and optimizing the design to reduce and control the residual stress, the aluminum alloy welded structure can be effectively manufactured. [ABSTRACT FROM AUTHOR]

Experiments were carried out in this paper first to clarify the characteristics of a digging process during aluminum alloy of type 5A06 variable polarity plasma arc welding (VPPAW). A special “Blasting type” penetrating phenomenon was observed through measuring the penetrating time by electrical and optical signals. A 3D model was established to numerically investigate heat transfer, fluid flow and surface shape during the digging process. An adaptive heat source was adopted to describe heat transfer process involving deformation of the keyhole tracked by volume-of-fluid (VOF) method. The plasma arc pressure attenuated in a parabolic form as the depth of the keyhole increases. It is found that the weld pool surface becomes concave after sufficient melting of metal. The keyhole depth exhibits responsive changes, which corresponds with the different stages of welding parameters. In the late stage, the depth increase rapidly to fully penetrating state, which shows a “blasting type” penetrating process. The keyhole formation was interpreted by considering energy accumulation and mass conservation of fluid flow. The maximum velocity during digging process always occurs on the keyhole surface, where a vortex in the opposite direction appears inside the weld pool. The calculated penetrating time, keyhole size and fusion line were basically in agreement with the experimental results. [ABSTRACT FROM AUTHOR]

• A S-curve power of laser oscillating welding is proposed. • The grains in the welded joint with S-curve power were refined, and the mechanism of grain refinement is analyzed. • Compared with joints with constant power, the tensile strength with S-curve laser power was increased by 35.3% and could reach 99.1% of the base metal strenght. Laser oscillating welding of 5A06 aluminum alloy is widely used in industry. In order to improve the performance of Al-based welded joints and reduce welding defects, this paper details the effects of employing an S-curve laser power which is distributed along the laser oscillating path (sine wave) to improve the microstructure and mechanical properties of the joints. By applying the S-curve and an equal power condition to the 5A06 aluminum alloy, bottom butt sinusoidal path laser oscillating welding was performed. The welding appearance, microstructure and mechanical properties of the welded joints under two laser oscillating welding processes were investigated. Our results showed that laser oscillating welding using the S-curve power allows to obtain good joints when compared to the joints produced with constant power. When the linearly varying laser power of "high-low-high" applied periodically was employed, the grains in the joint structure showed the cyclic "growth-inhibition-growth" phenomenon. This growth mechanism not only refined the grain structure, but also narrowed the columnar region, and improved the mechanical properties of the joint. Compared with the laser oscillating process with constant power, the tensile strength of the joints using the S-curve power was increased by 35.3 %. Moreover, the tensile strength of the welded test coupons with S-curve power was 337 MPa, which is about 99.1% of the base metal (340 MPa). The welded joints using the S-curve power showed larger and deeper dimples, highlighting higher ductility and good plasticity. This paper provides a new approach for the research of laser oscillating welding and the control of laser power to improve the mechanical properties of welded joints. [ABSTRACT FROM AUTHOR]