Research On The Formation And The Characterization Of Micro-porosity In Steel-aluminum Laser Weld

As an important subject of the 13th Five-Year planning,vehicle lightweight is of great significance to improve fuel economy and reducing C02 emissions.The composite structures of steel-aluminum can meet the requirements of lightweight body.But the properties of these materials are quite different,it is easy to produce internal micro-holes during the welding process,which affects the mechanical property of welded joint.By X-ray tomography,the three-dimensional distribution of micro holes can be obtained without destroying the samples.This paper focuses on the three-dimensional characteristics of the micro holes of steel-aluminum welding,and probes into the relationship between micro holes and mechanical properties,micro holes and welding process parameters.A series of steel-aluminum welding specimens were prepared by the fiber laser welding.X-ray tomography was used to obtain the 3D characteristics data of micro-pores.The 3D characteristics of porosities were analyzed.The micro-pores formation in welding joints was proposed.The micro-pore volume,number and sphericity were analyzed by mathematical statistics method.The results show that the deeper the penetration is,the lower the quantity of hole gets,the larger the maximum hole volume becomes.The majority of micro-pores in the weld pool are tiny holes with high sphericity which are the source of large volume holes.The volumes of the maximum pores of the major samples range from le-mm3 to le-3mm3.Mechanical properties tests were carried out for laser weld specimens.The relationship between the 3D characteristics of micro-pores and the mechanical properties was analyzed.The results show that the plus pore number and the maximum pore volume have significant influence on the mechanical properties.The method of response surface methodology(RSM)was used for establishing model to get the relationship between the 3D characteristics of micro-pores and the laser welding input parameters.The quadratic polynomial regression equation was established using the response surface method.Experimental results show that the equation can accurately predict the quality of steel-aluminum welded joints,optimize the laser welding parameters and improve the welding efficiency.