Jiankang Huang

Corrosion Behavior of Aluminum-Steel Weld-Brazing Joint

Dissimilar metals of 1060 aluminum and galvanized steel were joined with a lap joint by pulsed double-electrode gas metal arc weld brazing with aluminum-magnesium and aluminum-silicon filler metals. The corrosion behavior of the weld joints was investigated with immersion corrosion and electrochemical corrosion tests, and the corrosion morphology of the joints was analyzed with scanning electron microscopy (SEM). Galvanic corrosion was found to occur when the samples were immersed in corrosive media, and the corrosion rate of joints was increased with increased heat input of the workpiece. Comparison of the corrosion properties of weld joints with different filler wires indicated that the corrosion rate of weld joints with aluminum-silicon filler wire was larger than that of weld joints with aluminum-magnesium filler wire. Results also showed that the zinc-rich zone of weld joints was prone to corrosion. The corrosion behavior of zinc-rich zone was analyzed with SEM equipped with an energy-dispersive x-ray spectroscopy analysis system based on the test results.

Edge detection for aluminum alloy MIG welding pool based on pulse coupled neural network

Aimed at the problem of detection of pool edge for aluminum alloy MIG welding, a new method is adopted. The method is used to detect the pool edge of aluminum alloy MIG welding by applying the pulse coupled neural networks algorithm. The pulse coupled neural networks algorithm is introduced in this paper. The detection of pool edge for MIG welding pool is carried out with this algorithm by MATLAB. Then, the comparison between the result of PCNN algorithm and Canny detector is completed. The result indicates that the pulse coupled neural networks algorithm can be used to detect the process image of welding pool. And the image of pool edge by using the pulse coupled neural networks algorithm is clear and consistent. Besides, this new method can effectively overcome the influence of noise from welding pool image. The time of single frame processing is 54 ms.

Wire Extension Control Based on Vision Sensing in Pulsed MIG Welding of Aluminum Alloy

Research work of wire extension control based on vision sensing was done in pulsed MIG welding process of aluminum alloy. In order to resolve the actuality problem of traditional PID control, a self-tuning fuzzy PID controller was designed and a rapid prototyping control platform was established for pulsed MIG welding of aluminum alloy using real-time target environment based on xPC. With vision sensing of welding zone image and corresponding image processing algorithm, a fuzzy PID closed loop control system for wire extension was designed on the basis of the built rapid prototyping control platform. Experimental results show that the method of vision sensing can meet the control requirements of wire extension stability, the rapid prototyping control system built with fuzzy PID controller based on vision sensing can realize well the control of the wire extension in pulsed MIG welding of aluminum alloy and also has strong robustness and quick response ability.

Modeling, simulation and control of pulsed DE-GMA welding process for joining of aluminum to steel

Joining of aluminum to steel has attracted significant attention from the welding research community, automotive and rail transportation industries. Many current welding methods have been developed and applied, however, they can not precisely control the heat input to work-piece, they are high costs, low efficiency and consist lots of complex welding devices, and the generated intermetallic compound layer in weld bead interface is thicker. A novel pulsed double electrode gas metal arc welding(Pulsed DE-GMAW) method is developed. To achieve a stable welding process for joining of aluminum to steel, a mathematical model of coupled arc is established, and a new control scheme that uses the average feedback arc voltage of main loop to adjust the wire feed speed to control coupled arc length is proposed and developed. Then, the impulse control simulation of coupled arc length, wire feed speed and wire extension is conducted to demonstrate the mathematical model and predict the stability of welding process by changing the distance of contact tip to work-piece(CTWD). To prove the proposed PSO based PID control scheme’s feasibility, the rapid prototyping experimental system is setup and the bead-on-plate control experiments are conducted to join aluminum to steel. The impulse control simulation shows that the established model can accurately represent the variation of coupled arc length, wire feed speed and the average main arc voltage when the welding process is disturbed, and the developed controller has a faster response and adjustment, only runs about 0.1 s. The captured electric signals show the main arc voltage gradually closes to the supposed arc voltage by adjusting the wire feed speed in 0.8 s. The obtained typical current waveform demonstrates that the main current can be reduced by controlling the bypass current under maintaining a relative large total current. The control experiment proves the accuracy of proposed model and feasibility of new control scheme further. The beautiful and smooth weld beads are also obtained by this method. Pulsed DE-GMAW can thus be considered as an alternative method for low cost, high efficiency joining of aluminum to steel.

Using priority growth orientation of crystallite of the Monte Carlo method to study the process of crystal nucleation and growth in liquid phase

The technique of “crystallite growth preferred orientation” was presented based on the Monte Carlo (MC) simulations of grain growth, and its factor was used to establish a lattice coordinate tracking method. The nucleation and growth of crystal from the liquid phase throughout the whole simulation were examined. Changes in solid fraction and crystallite size were counted via simulation by lattice tracking. Results showed that the established model could properly reflect crystallite nucleation and growth. The model was also determined capable of accurately estimating the number of solid phase fraction and achieving change in crystallite size by the lattice tracking method. The change in solid fraction and MC step (MCS) satisfied the S curve during simulation. The crystallite growth index was 0.477, which was relatively close to the theoretical value of 0.5.

Welding Technology Analysis of Bypass Coupling Micro Plasma Welding

The method of bypass coupling micro plasma welding was introduced, and used for the research of surfacing welding experiment. Different welding parameters were investigated, the thermal cycling curves were test, and the microstructure was observed. The result shows, with the increase of bypass current, the highest temperature of thermal cycling curves decreased and the microstructure was much fine. Therefore, we could speculate that the heat input to base metal is decreasing with the increase of bypass current. The bypass coupling micro plasma welding can achieve the accurate control of arc heat, balance the heat input to base metal and welding wire. Compared with traditional micro plasma welding, bypass coupling micro plasma welding can accurately control the heat input to base metal under the condition of constant heat input.

Effects of powder on microstructure, tensile, and corrosion behavior of aluminum-steel joints

Using laser welding-brazing technique to join 5A06 Al alloy and ST04Z galvanized steel, the authors study the effect of adding pure powder (Si, Mg, Mn, or Zn) in the joining on the material behavior of welded joints. The results show that the microstructures, tensile behavior, and corrosion behavior of the welded joints are dependent on the powder used in the welding. An intermetallic compound (IMC) layer consisting of Fe2Al5 and FeAl3 is formed between the Al alloy and the steel, which is independent of the pure element powder used. The IMC layer with the use of Zn powder has the least thickness. The welded joints with the use of pure Mg element powder have the largest corrosion resistance.Using laser welding-brazing technique to join 5A06 Al alloy and ST04Z galvanized steel, the authors study the effect of adding pure powder (Si, Mg, Mn, or Zn) in the joining on the material behavior of welded joints. The results show that the microstructures, tensile behavior, and corrosion behavior of the welded joints are dependent on the powder used in the welding. An intermetallic compound (IMC) layer consisting of Fe2Al5 and FeAl3 is formed between the Al alloy and the steel, which is independent of the pure element powder used. The IMC layer with the use of Zn powder has the least thickness. The welded joints with the use of pure Mg element powder have the largest corrosion resistance.

Study on Dynamic Development of Three-dimensional Weld Pool Surface in Stationary GTAW

Abstract The weld pool contains abundant information about the welding process. In particular, the type of the weld pool surface shape, i. e., convex or concave, is determined by the weld penetration. To detect it, an innovative laser-vision-based sensing method is employed to observe the weld pool surface of the gas tungsten arc welding (GTAW). A low-power laser dots pattern is projected onto the entire weld pool surface. Its reflection is intercepted by a screen and captured by a camera. Then the dynamic development process of the weld pool surface can be detected. By observing and analyzing, the change of the reflected laser dots reflection pattern, for shape of the weld pool surface shape, was found to closely correlate to the penetration of weld pool in the welding process. A mathematical model was proposed to correlate the incident ray, reflected ray, screen and surface of weld pool based on structured laser specular reflection. The dynamic variation of the weld pool surface and its corresponding dots laser pattern were simulated and analyzed. By combining the experimental data and the mathematical analysis, the results show that the pattern of the reflected laser dots pattern is closely correlated to the development of weld pool, such as the weld penetration. The concavity of the pool surface was found to increase rapidly after the surface shape was changed from convex to concave during the stationary GTAW process.

Simulation of Decoupling Control of Pulsed MIG Welding for Aluminum Alloy

Based on system identification of pulsed MIG welding process for aluminum alloy, due to strong coupling among the welding parameters, PID controller, fuzzy PID controller and neural network inverse controller were designed, the strong coupling multi-input and multi-output (MIMO) system was simulated using pulse current duty cycle and wire feed speed as control input, and wire extension and pool width as control output. The results show that the neural network inverse control provides faster response and better robustness, which lays a foundation for decoupling control of aluminum pulsed MIG welding.

Modeling and Decoupling Control Analysis for Consumable DE-GMAW

Aiming at the instability of dynamic welding arc and strong coupling among welding parameters, a mathematical model for consumable double-electrode gas metal arc welding (DE-GMAW) was established by the method of equivalent path and then dynamical analysis was carried out. On this basis, an approach was proposed to control the stability of the welding arc using the wire extensions of main and bypass torch as a control object. And then a comparative analysis of two different decoupling control schemes was made respectively using the bypass wire feed speed and the bypass current as input and using the wire feed speed of main and bypass as input. The results show that the mathematical model can reflect the process of consumable DE-GMAW well and the decoupling control scheme using the wire feed speed of main and bypass as inputs has better dynamic performance and robustness.