Study On Weldability And Mechanical Properties Of Al-Zn-Mg Alloy Fillet Welds

The research and development of high-speed trains in our country are in a stage of rapid development,as one kind of the Al-Zn-Mg alloys 7N01 Aluminum Alloy while meeting the requirements of lightweight manufacturing because of its excellent mechanical properties are widely used in high speed train underframe bolster and anti yaw movement of key parts such as shock absorber.Due to the requirements of lightweight and anti deformation properties usually can only be welded joint containing fillet weld connection,multi-dimensional stress loading and joint structure cause that the connector has become the key of the underframe connection and weak parts.In this study,based on the comprehensive performance of lap,T type,cross(contact weld),cross(work seam)of 7N01 Aluminum Alloy and the heavy plate,provide a scientific basis for high quality manufacturing of high speed train.In order to investigate the performance of welded joints with fillet welds in the multi direction bearing service process,making comparative,multi angle analysis of four kind of joints on static properties and microstructure.Obtained the comparable results on tensile strength,bending properties and microscopic properties of the local areas between different joints.The macro performance differences are analyzed from the microstructure point of view.The regularity results in the experiment are analyzed theoretically.The static load performance of fillet weld joint is summarized comprehensively.The main failure mode of welded structures in high-speed trains is fatigue failure behavior,in order to investigate the difference of fatigue properties between different types of fillet welds,the fatigue tests of four joints with different maximum stress levels were carried out.The fatigue properties of the joints were calculated and compared.The specimens with fatigue fracture were observed and analyzed by macroscopic and scanning electron microscopy.The fracture mode was judged,and the law of fatigue crack growth was expounded.In combination with the fatigue performance test,the comparative fatigue strength results of the four joints and the regularity that the fatigue specimens were broken in the weld toe instead of the welding root were observed.Based on the notch stress method,the finite element simulation software Abaqus/CAE was used to fit the four joints,andthe stress distribution in the local part of the notch was simulated,and the notch stress intensity factor was calculated,by correlation theory,it is transformed to mean strain energy density and compared.The local average strain energy density of each joint is obtained,that is,the stress distribution is inversely proportional to the fatigue limit.As a welding base plate,aluminum alloy is made by rolled process.Because of the stress of welding thermal process and the influence of low melting material agglomeration,there may be dangerous cracks such as liquefaction cracks during the welding process.In order to investigate the tendency of the failure form,the Z window test was carried out.The restraint effect of fillet weld on aluminum alloy was enlarged.The distribution of low melting point substance and element content was analyzed by scanning electron microscope and line scanning.According to the theory of high temperature ductility,it is found that the rolling direction perpendicular to the aluminum alloy is the dangerous orientation of its high temperature load.