Laser Direct Joining Of Aluminum Alloy And PBT

In recent years,the application of polymers and lightweight metals in the lightweight design of industrial structures has become more and more extensive,which makes the joining of polymers and metals one of the key technical issues.Laser direct joining technology is an effective means to solve this problem,and it has become a research hotspot in the joining of polymers and metals.In this dissertation,the aluminum alloy has the characteristics of high reflectivity and high thermal conductivity.By blackening the upper surface of aluminum alloy to improve its absorption of laser energy,and by laser oxidation treatment and laser texture treatment on the lower surface to improve the joining strength of laser direct joining of aluminum alloy and PBT,the dissertation explored the joint mechanism and optimized the process parameters.The main research contents and results are as follows:Firstly,the upper surface of the aluminum alloy is blackened.Experimental research has found that the blackened aluminum alloy and PBT are directly joining by laser under low power conditions.Although the joining strength is not high.However,the problem of low laser energy absorption rate of aluminum alloy illumination surface is solved for the subsequent process research of improving the laser direct joining strength.Research on the process and mechanism of laser direct joining aluminum alloy and PBT based on laser surface oxidation treatment: The lower surface of the aluminum alloy was oxidized,and the single-factor experiment was carried out on the joining of oxidized aluminum alloy and PBT.The experimental results show that the joining strength increases first and then decreases with the increase of welding power and speed.When the scanning distance of oxidation decreases and the power of oxidation increases,the joining strength increases.By observing the cross-section morphology of the joint,it is found that when the power is too high,the large bubble generated by the decomposition of PBT will reduce the strength of the joint.The study of bonding mechanism shows that the micro-nano structure is formed on the surface of aluminum alloy after oxidation treatment,and the surface roughness increases obviously.These changes are helpful to enhance the anchoring effect.The surface contact angle experiment found that the oxidation treatment effectively improved the wettability of the aluminum alloy surface,facilitated the wetting and spread of the molten PBT on the aluminum alloy surface,and promoted the anchoring joint between the aluminum alloy and the PBT.XPS analysis shows that the increase of oxygen content on the surface of aluminum alloy is due to the formation of a new Al2O3 layer on the surface,which promotes the formation of Al-O-C and Al-C chemical bonds between aluminum alloy and PBT,and the chemical bonding can effectively improve the joining strength.Research on the process and mechanism of direct joining aluminum alloy and PBT based on laser surface texture treatment: Among the three texture features of horizontal lines,vertical lines and grids,the aluminum alloy treated with grid texture has the highest joining strength with PBT.The effects of welding power,welding speed,times of texture scanning and texture density on the joint strength were investigated by single factor experiments.The results show that the joining strength increases first and then decreases with the increase of these four factors.Observing the cross-sectional morphology of the joint,it is found that the large bubbles generated by the decomposition of PBT will reduce the joining strength when the power is too high;When the number of scans is excessive,the heavy condensate accumulated on the inner wall of the groove hinders the inflow of the melted PBT,which is not conducive to the formation of the anchoring effect;XPS analysis showed that there were new chemical bonds Al-O-C and Al-C at the interface,but their chemical bonding strength was weak,the strength of direct joining of aluminum alloy and PBT was improved mainly through the anchoring effect.Process parameter optimization research: Comparative analysis found that the joining strength of composite treated aluminum alloy and PBT is not significantly improved compared to the joining strength of textured aluminum alloy and PBT,but both are better than the joint strength obtained by laser surface oxidation treatment.and the time required for the texture treatment is 1/3 of the oxidation pretreatment time.It is concluded that the effect of the texture treatment process is better,so this dissertation chooses to optimize the process parameters of the direct joining of the texture treatment aluminum alloy and PBT.The mathematical model of joining strength and pretreatment time were established by response surface method.and analyze the interactive influence of each process parameter combination on the joining strength,It was found that the interaction effects of welding power-texture density and welding powerwelding speed on the joining strength were more significant.It was found that the predicted values of the model were in good agreement with the experimental values,which indicates that the established model had high reliability.Two criteria were used for multi-objective optimization,and the corresponding optimal process parameters were obtained respectively.This dissertation lays the theoretical foundation and provides technical support for the practical industrial application of the laser direct joining of aluminum alloy and PBT.Furthermore,it also provides new ideas and new methods for the improvement of the laser direct joining strength of other metals and thermoplastic polymers.