The Study On Local Deformation And Fracture Behaviors For Aluminum Alloy Welded Joints

The application of aluminium alloy in the auto-mobile is more and more extensive due to their low density, good plasticity and high strength/weight, and welded joint is the weak position in the automobile body structure. The joints exhibit heterogeneity of mechanical properties, so accurate measuring the local mechanical properties is essential to improving the welding craft and evaluating properties of the whole joint, and realizing the local deformation and fracture behaviors in the process of loading is significative to designing strength of joints and performing collision tests. This paper connects 6063 aluminum alloy welded joints to this situation.(1) Design a double-hole microshear test device which consists of loading part, blanking part, metallographic observation part and operation platform. Its function is to measuring the materials' local mechanical properties.(2) Using the test device to make double-hole microshear test, and using the finite element analysis to measure joints' local mechanical properities. In addtion, establish the finite element model of double-hole microshear test.(3) In the process of loading, observing the grain deformation, crack initiation, expansion and connectivity until fracture, and SEM photos of fracture to study local deformation and frcture behaviors in the joints.(4) Design two samples. Under the condition of stress state varying, make double-hole test to study local deformation and frcture behaviors in the joints, and establish the finite element model.The result of study shows :1) The double-hole microshear test device can meet the test requirements.2) Measure the fracture strain at the different zone of 6063 aluminum alloy butt welding joints. The results show: the welding seam zone' fracture strain is the least, and the base material zone is the most. But at the HAZ, with the increase of distance, the fracture strains are gradual increscent. At one time, determining the distribution of joints' yield strength and work hardening index. When the yield strength is the lowest, work hardening index is the highest; and when the work hardening index is the lowest, yield strength falls a little.3) At the same aperture, materials' fracture strain is bigger, then at the different aperture, materials' fracture strain is smaller. At the same aperture, the specimen's crack locates the point that loading starts to fall in the process of loading, after the crack come into being, loading begins to fall quickly, then the specimen will rupture in succession. Materials' damage is: In the process of loading, localization shear bands will appear firstly, then microcracks will produce in the inside of localization shear bands, with the increase of deformation, microcrack 新制度主义;行政问责制度体系;制度...