| The lightweight design of automobile is one of the core directions of the future development of automobile industry.The laser direct connection technology of metal and plastic is of great significance to the lightweight design of automobile.Low laser welded joint strength of metal and plastic is a technical problem.In this paper,femtosecond laser processing technology was used to fabricate micro-structures on metal surface.The systematic research of laser welding of metal and plastic based on micro-structures was carried out through analysis of laser welding experiment and simulation of temperature field.The influence of array types and size parameters of the micro-structures on the welded joint strength was studied.The priority of the influence of different micro-structures parameters on welded joint strength was explored through orthogonal test analysis.A set of microstructures parameters were optimized based on orthogonal test.The influence of laser process parameters based on micro-structures on welded joint strength was investigated.A three-dimensional transient finite element model based on micro-structures was established to investigate the influence of laser and micro-structures coupling on temperature field in welding process.The main research contents are as follows.Firstly,the experimental materials were prepared,and the mechanical properties and thermal physical properties of 30%glass fiber reinforced PA66 were tested.The technology of preparing surface micro-structures by femtosecond laser was explored.The effect of femtosecond laser processing parameters on the size of micro-structures was investigated.Femtosecond laser processing parameters include:laser average power,scanning speed,scanning times.The process exploration provides technical support for the processing of aluminum alloy surface micro-structures.Secondly,the micro-structures of different array types were processed on the metal surface and then laser welded with plastic.The influence of surface micro-structures on laser welded joint strength of aluminum alloy and PA66 was investigated,and the type of microstructures array was optimized.The surface micro-structures machining can effectively improve the laser welded joint strength of aluminum alloy with PA66 compared with untreated aluminum alloy.Weldments with mesh array micro-structures obtain maximum welded joint strength,and the maximum tensile shear load is 1062.26 N.The welded joint strength is about 4 times that of untreated aluminum alloy weldments.The main reason for the improvement of welded joint strength is the micro-riveted joint is generated at the interface between metal and plastic after surface micro-structures treatment.The formation of micro-riveting structure increases the area of metal and plastic connection.C-O-Al bonds was generated on the interface between aluminum alloy and PA66 during laser welding.The formation of new bonds is beneficial to the welded joint strength.The increase in the area of metal-plastic connections is conducive to increasing the number of new bonds produced.Thirdly,the influence of surface micro-structures parameters on laser welded joint strength of metal and plastic was investigated based on mesh array micro-structures.Microstructures parameters include width,depth and spacing.The results show that the welded joint strength of metal and plastic is related to the filling effect of micro-structures.The priority of the influence of various factors on welded joint strength was discussed by orthogonal test.The influence of micro-structures parameters on the strength of laser welded joints priority from large to small:micro-structures width,micro-structures depth,microstructures spacing distance.A group of optimal micro-structures parameters were selected based on the orthogonal test interval,which were 200 μm in width,300 μm in depth and 150μm in distance.The influence of laser process parameters on welded joint strength was investigated based on the micro-structures parameters.It was found that the melting amount of plastic is less under low laser input energy and the micro-structures cannot be fully filled.The higher laser input energy causes the thermal decomposition of plastics to produce welding defects,which is adverse for welded joint strength.Finally,a three-dimensional physical model based on micro-structures was established,and the transient temperature field of laser welding of metal and plastic based on microstructures was simulated.The influence of micro-structures on temperature field and the variation of temperature field with time and laser welding process parameters were investigated.The results show that the micro-structures slow down the thermal diffusion rate and the high temperature region is more concentrated.The melting zone of plastic expands and the melting time increases with the increase of laser input energy.However,the high input energy makes the temperature of some regions inside the melting exceed the thermal decomposition temperature.The accuracy of numerical simulation was verified by comparing simulation results with experimental results. |
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