Papers by Author: Xi Jing Wang

Abstract: Friction stir welding (FSW) was a new solid-state metal-joining method and force played an important role in the weld forming. The study of dynamic stress field helped to understand the forming mechanism of FSW and residual stress after welding. Regarding FSW of aluminum alloy, this paper built the finite element model which was based on DEFORM-3D software and achieved numerical simulation of the dynamic stress field in the FSW process. The results indicate that the peak of stress field appeares in the front side of weld and distributed asymmetrically along the center of the weld; the axial force playes an important role to the distribution of stress field, the the distribution of stress field becomes more intensive as the downforce largen; the stress gradient of the advancing side of weld changes larger than that of the retreating side; the stress near the shoulder experiences twice peak.

Abstract: The fatigue properties of refill friction stir welding joints of 6082-T6 aluminum alloy were completed based on the optimal process parameters. The expression of the fatigue life prediction were obtained in a certain range. The microstructure and fatigue fracture appearance of welding joints were observed and analyzed. And the microhardness of the joints were tested. The results showed that the fatigue crack initiated from the root of the joints between the lower and upper plate, that is the junction of HAZ and TMAZ, and then propagated to fracture along the boundary between the HAZ and the TMAZ. Strengthening phase which was formed of trace elements significantly affected the fatigue properties of spot welding joints. The fatigue life of spot welding joints along with stress intensity factors decrease showed an increasing trend. Fatigue life of spot welding joints emerge an increasing trend along with decreases of the load.

Abstract: For the friction stir welding technology of the low carbon steel, according to the character of the friction stir welding process, the researchers build a simplified heat input numerical model, and use the finite element analysis software ANSYS to simulate the transient temperature field distribution and the feature points of thermal cycle curve of the 4 mm Q235A steel in the butt joint. Comparing the simulation results and the feature point temperature curve measured by the thermocouple, the researchers verify the heat input model and simulation method is correct. It provides the scientific basis to select the right experimental parameters.

Abstract: AZ31B magnesium alloy, Rotating tool without pin, Friction Stir Spot Welding, Microstructure, mechanical properties

Abstract: Friction Stir Welding (FSW) is a new and developing technology that has been used succefully in the joining of aluminum and aluminum alloys.To demonstrate the feasibility of the auxiliary power of Q235 steel friction stir welding, we used orthogonal test method to design auxiliary power FSW parameter,then welded 200mm×80mm×4mm of Q235 with the parameter. The result shows that the rotating 1200 r/min, the stay time 10s and the heating temperature 700 °C,the welding joint tensile strength can reach 332.19 MPa. Analysing the parameter fracture morphology,we found that the fracture is divided into three levels: the upper part is the ductile fracture; the middle part is the combination of the ductile fracture and the brittle fracture;the lower part is the majority of the brittle fracture, and exists the local ductile fracture. Analysing the microstructure,we found that welding joint is divided into the base zone, the heat affected zone,the thermo-mechanically affected zone and the stir zone,and the microscopic organization of every area is influenced by the heat and the force on the area. The microhardness of stir area improves 12% on average than the base’s.The microhardness of the heat affected zone and the thermo-mechanically affected zone decreases , comparing to the base’s.

Abstract: At present, the main methods used to predict welding residual stresses are the three dimensional thermo-elastic-plastic FEA method and the inherent method.Many learners had simulated the residual stresses of FSW used the thermo -elastic-plastic FEA method which was proved to be time consuming and not very effective. The inherent strain method neglects the whole welding process, and predicts distortion using an elastic finite element analysis by applying the inherent strains on the structure. In this paper,the inherent strains are firstly obtained for an flat butt-joint of aluminum alloy through experiments and three dimensional thermo-elastic-plastic FEA. Computational and experimental results showed that the inherent strain method could predict welding distortion with acceptable accuracy and greatly reduced running time when comparing to the thermo-elastic-plastic FEA method.

Abstract: Dissimilar metal of Steel and Magnesium alloy used for friction stir spot welding is studied. Based on using orthogonal test method optimizes the process parameters and gets satisfactory joints , SEM is used to observe the features of joint,XRD is applied to determine the joint phase, and the results show that: the design of rotating tool without pin is reasonable and it can form satisfactory joints without keyhole of spot welding. The performance of spot welding joint depends on the extent of diffusion of Zn and Mg and high weld consistency. There is small existence of intermetallics made of MgZn2,Mg0.97Zn0.03 in welding joint.The properties of joint depends on the intermetallics, Due to this,The microhardness of joint increases gradually from the magnesium side to steel side.

Abstract: Friction stir blind riveting (FSBR) is a new joining process which eliminates the need to predrill a hole for rivet insertion. Lap joint friction stir blind riveting the plates made of high strength steel DP600 (1 mm) and magnesium alloys AZ31B(3 mm) with different technological parameters was carried out. This study experimented with the strength and the morphology of the joint with different rotation speed and feet rates of the spindle rivet, and which material on bottom or top. The main results obtained are as follows: FSBR’s process of steel and magnesium alloy plate was quickly and successfully achieved. The maximum shear strength of the joint reached about 6.3KN and the fracture path was along the shank of rivet. When Mg plate is on top of the other, the spindle speed is 2,200rpm, and along with the increase of the feed rates, the gap of plates is decreased, the strength of joint is increased. When steel plate is on top layer, the spindle speed at 2,200rpm, the rivet can then plug into the plates with a feed rate at least 600mm/min, and the joint shear strength will become higher.