Deformation And Damage Behaviour Of 6063 Aluminum Alloy T-welded Joints

Lightweight aluminum alloy body frame structure is direction of development on energy-saving environment-friendly vehicle, Studying of weld ability of aluminum alloy and analysis of mechanical properties of aluminum alloy welded joint and its changes is a hot topic. Fillet welded structure is the main form of connectivity, the fillet formed by the T-welded joints has been widely used in the aluminum frame body connection. However, the complexity of its organization, performance and stress state affect the performance of entire body of the framework. Around these issues, a series of tests were carried out, including tests of mechanical properties, scanning of electron microscope of the fracture surface and combination of finite element simulation method for single-sided aluminum alloy 6063 weld T-joints:First of all, considering the anisotropy effect of extrusion 6063 aluminum alloy, the characterization on mechanical property in different angle to the extrusion direction of material has been implemented in this paper. At the same time, the characterization provides a necessary theory foundation for sampling modes in the following experiments and finite element simulation. Tensile and shear tests of 6063 aluminum alloy were performed for material mechanics performance characterization. Macroscopic test showed that fracture strain of plate tension was larger than that of notched plate tension, but when just the opposite of pure shear tension; however, the yield stress of plate tension was lesser than that of notched plate tension. Observed the fracture surface of the pulled off sample, the dimple mechanism was increasing and shear mechanism was decreasing with stress triaxiality enhancing. Fracture mechanism of notched plate tension was dimple, but large shear dimple and shear facet were observed in shear test, however shear fracture mechanism and tension fracture mechanism mixed for plate tension test, eventually the fracture mainly due to shear fracture, shear fracture occurred on width or thickness in microscopically; Tension fracture occurred in notch tension test. Stress states also considered when choosing the damage model. In addition, damage parameters depended on size of mesh.Secondly, double micro-shear tests of aluminum alloy T-joints were carried out for characterization of the partial mechanical properties of materials. Using TIG welding method, preparation of alloy T-joints for the test. As a result of the micro-joints and mechanical properties of a large difference. The use of double micro-shear method of T-joint board and the legislature of measuring the width of micro-plate and characterizing of the material properties. The results showed that: The designed double micro-shear device can test the local material properties of T-joints. Repeatability of test results of its greatest error is not more than 1.07%. And simple sample preparation, high test accuracy; combination with finite element inverse method and experiment, access to the micro-parameters of mechanical properties and the parameters of Johnson-cook model of the joint, provide a basis for modeling the T-joint mechanical of finite element simulation.At last, three-dimensional solid modeling—Solidworks software was used to design T-joints to achieve different angles of tensile test specimen and fixture, and tensile test and fracture surface were observed. The results show that there is a "small platform" of the four curves in the process of plastic deformation except 0 degrees. Moreover, the displacement of the specimen increased with the load increased, This is the weak links and the local impact caused by defects bring in the welding process. Observation of the fracture surface of the pulled off sample discovered that: 0 degree tensile specimen have a smooth flat surface and the dimples and the plate shear have obvious direction on legislative board fracture, but the bottom shear fracture was absence of such characteristics, because of the specimen in the process of tension through the course of stretching—bending—fracture. 45 degrees tensile fracture surface was form of a large number of elongated dimples and some smooth shear flat. Fracture caused by both the normal stress and shear stress. 90 degrees tensile fracture surface was formed of a large number of dimples gathered in the center and the of shear flat areas of the edge. 30 degrees and 60 degrees were formed of a certain amount of dimples and shear fracture plane, only 30 degrees surface has more tensile shear distribution. It can be seen, T-joint tensile specimen in the course has certain role of torque and bending moment. Join the G-T-N damage model of T-joint injury in the conduct of the finite element analysis, the results shows: the G-T-N damage model both can be used to simulate the damage behavior of T-joints under different stress state, but the forecast results of the G-T-N damage models are better than that of the Johnson-cook damage model.T-joint test and finite element simulation have practical value for simulation and analysis of vehicle collision in the future. But to achieve the accuracy of finite element simulation, achieve the continuous of the material properties of welded joints are need, This need begin with welding simulation, Analysis of the welding simulation data as a prerequisite for simulation of mechanical properties, establish a welding material model.