Laser Direct Joining Of Aluminum Alloyand Fiber Reinforced PA66 Based On Surface Texture And Ultrasonic Assistance

Due to their excellent physical and chemical properties,polymers and lightweight alloys have been widely used in the field of lightweight design in recent years,which leads to the inevitable need for connection between them.Laser direct connection technology is one of the most effective means to realize the connection of dissimilar materials.In this thesis,aluminum alloy(A5052)and glass fiber nylon(PA66GF30)were connected by laser direct connection technology,and the surface of aluminum alloy was treated with texture and ultrasonic vibration was applied in the process of laser connection to improve the connection strength of the joint.The connection mechanism was explored and related process parameters were optimized.The main research contents and achievements of this thesis are as follows:(1)Direct laser connection between A5052 and PA66GF30 based on surface texture treatment: Among the horizontal,vertical and circular texture characteristics,the circular texture treatment has the highest enhancement effect on the joint strength of A5052 and PA66GF30,and the joint strength reaches 2.2 times of that of direct laser connection.Through single factor experiments,it is found that the joint strength of aluminum alloy and PA66GF30 firstly increases and then decreases with the increase of laser power,laser connection speed and texture scanning times.Through the observation of the cross section morphology of the joint,it is found that when the laser connection speed is low and the laser power is high,the bubbles generated in the molten pool have larger microstructure and pile up at the joint surface of aluminum alloy and PA66GF30,which reduces the actual bonding area between materials and reduces the connection strength of the joint.With the increase of texture scanning times,the remelted aluminum alloy flows into the interior of the texture groove,hindering the inflow of melted PA66GF30,which is not conducive to the formation of mechanical anchoring effect.XPS analysis showed that there was a new chemical bond at the joint surface: Al-O-C and Al-C,but the chemical bond strength was weak.It was mainly due to mechanical anchorage effect that improved the joint strength of A5052 and PA66GF30.(2)Direct laser connection between A5052 and PA66GF30 based on ultrasonic vibration assistance:(1)The results show that ultrasonic vibration in the process of laser connection has the best effect on the joint strength,the joint strength reached 1.39 times of the laser direct connection,but the application of ultrasonic in the cooling stage will reduce the joint strength.Through the observation of the cross section morphology of the joint,it is found that the low power ultrasonic vibration has no obvious effect on the bubble structure in the weld pool.With the increase of ultrasonic power,the bubble structure inside the molten pool gradually becomes fine and uniform,which is conducive to the improvement of connection strength.When the ultrasonic power is too high,some small bubbles gather into new large bubble tissue and accumulate at the joint surface of A5052 and PA66GF30,which reduces the joint strength.(2)Co MPared with the composite process of ultrasonic vibration,the joint strength of surface texture treatment is higher than that of single process,and the joint strength is 3.11 times of that of direct laser connection.Ultrasonic vibration can improve the fluidity of melting PA66GF30,improve the filling degree of melting part of PA66GF30 on the texture groove,and form a more stable mechanical connection.(3)XPS analysis shows that there may be a new chemical bond at the junction surface,but the chemical signal is very weak;The mechanical anchorage effect mainly improved the joint strength of A5052 and PA66GF30.(3)Modeling and optimization of process parameters: Through co MParative analysis,it was found that among the three process methods(surface texture treatment,ultrasonic vibration and the composite process of surface texture treatment and ultrasonic vibration),the composite process of surface texture treatment and ultrasonic vibration enhanced the joint strength the most.Therefore,the process parameters of the composite process were designed and optimized.The mathematical models of process parameters,joint strength and pretreatment time were established by response surface method,and the variance analysis of the models showed that the reliability of the models was high.After the selection of process parameters,it is concluded that the four process parameters that contribute the most to the connection strength are laser power,texture scanning times,ultrasonic power and circular texture diameter.In the pairwise combination of four process parameters,the interactive effects of laser power and ultrasonic power,laser power and texture scanning times,texture scanning times and ultrasonic power are the largest.Two different optimization criteria were selected for single objective and multi-objective optimization of process parameters,and the corresponding optimal parameter combination was obtained respectively.