Xi Jing Wang

A Technological Study on Friction Stir Blind Rivet Jointing of AZ31B Magnesium Alloys and High-Strength DP600 Steel

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.

Lap Joint Properties of FSBRed Dissimilar Metals AZ31 Mg Alloy and DP600 High-Strength Steel with Various Parameters

The Friction stir blind riveting (FSBR) process consists of a blind rivet is driven at high rotational speed and brought into contact with the workpieces, thereby generating frictional heat between the rivet and the workpiece, which softens the workpiece material and enables the rivet to be driven into the workpieces under reduced force. The riveting of lap joint of AZ31B(3mm) magnesium alloys plate and a DP600 (1mm) high strength steel plate was produced by FSBR using 2200rpm rotation speed, various feet rates and different lap mode to investigate the effects of the joint morphology and strength. The joint strength depended strongly on the shank of rivet itself shear strength，however in which case the strength of joint impacted by rivet assembly quality (the lap of plates, the tightness rivet of workpiece). So positioning the steel sheet on the top is desirable, the maximum shear strength of the joint reached about 6.0KN.

Dissimilar Friction Stir Spot Welding without Key Hole between AZ31B Magnesium Alloy and 5052 Aluminum Alloy

To study the impact of the welding process parameters on the spot weld surface molding, mechanical performance and the stir zone microstructure, we use friction stir spot welding without keyhole method which designed and developed by ourselves to carry on the lap welding between 1mm sheet of AZ31B magnesium alloy and 3mm sheet of 5052 aluminum alloy with magnesium on top and aluminum bottom. The result of the orthogonal test shows that the shoulder friction time have a greater impact on the forming of the surface of the welding joint; When the rotating speed of 1000 r/min, shoulder friction time of 4s, pin length of 3.5mm, the tensile shearing force of the welded joint achieves its maximum value of 2.46 KN.Through observating the microstructure of the welding joint’s section stirring zone, we found the typical joint microstructure of Dissimilar metal. Through analyzing the microstructure of the tensile fracture, we found that fracture was cleavage fracture.We also found the fracture mechanism of the welding joint was cleavage fracture in microcosm but brittle fracture macrocosm.

Study of Friction Stir Spot Welding of Steel/ Magnesium

Dissimilar metal of Steel and Magnesium alloy by friction stir spot welding is studied. Based on using orthogonal test method to optimize the process parameters and get satisfactory joint, SEM is used to observe the features of joint, fracture morphology, and XRD is used 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 for spot welding; spot welding nugget zone on the magnesium side shows the phenomenon of melting and solidification in the range of hundreds microns, and its microstructure appears a structure of dendrites; The fracture mode of spot welding joint is a mixed mode of cleavage and dimpled rupture.

The Temperature Field Test and Numerical Simulation of Steel’s Friction Stir Welding Process

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.

A Preliminary Investigation on Friction Stir Spot Welding of Steel/Mg

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.

Comparison of Properties on Withdrawing and Refill Friction Stir Spot Welding Joints

The 2 mm sheet of 6082 - T6 aluminum alloy was carried to develop refill friction stir welding and withdrawing friction stir spot welding,the forming of solder joints , the cross-sectional microstructure and fracture morphology of welding joints were observed and analyzed, the cross-sectional microhardness of welding joints were tested. Tensile shear load and fracture mode were contrasted simultaneously. The results showed that smooth surface and free of macroscopic defects of welding joints could be obtained in both welding type. Tensile shear load of WFSSW was up to 10.28kN under the optimal process parameters greater than RFSSW’s 8.62kN.

The Study of the Microstructure and Mechanical Properties of Friction Stir Spot Welding Joint between AZ31B Magnesium Alloy and Steel

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

The Research of the Auxiliary Power of Q235 Steel Friction Stir Welding Technology and Joint Microstructure’s Observation

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.

Comparison of Different Residual Stress Models of FSW Butt Joints for Thin Aluminum Alloy Plates

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.