| As the demand for light-weighting of industrial engineering,dissimilar light materials for making multi-material lightweight structures have been widely applied in aerospace,automobile and other fields.Titanium alloy with high specific strength and high-temperature stability have attracted the attention in aerospace industry.Carbon fiber reinforced thermoplastic(CFRTP)was considered as the alternative engineer material due to excellent specific strength and low density.High-strength joining of two materials could not only meet the requirement of light-weighting,but also promote the development of multi-material lightweight structures.In this paper,laser heat conduction joining process was selected to join the base materials include 1.5mm-thick Ti-6Al-4V titanium alloy(TC4)and 2mm-thick carbon fiber reinforced polyether-ether-ketone(CFRTP).The effect of joining processes on laser joining of CFRTP to TC4 and the joining mechanism were clarified.The interfacial joining strength was improved by surface dual scales include mechanical interlocking in micrometer scale and chemical bonding in nanoscale reinforcement process according to the joining mechanism.Firstly,the influence of laser joining process parameters on the strength of TC4/CFRTP joint was discussed.The result indicated that the laser joining mechanism of TC4 and CFRTP was mainly composed of interfacial mechanical interlocking and chemical bonding.The shear force of TC4/CFRTP was correlated with the bonding width of the resin and adhesion ratio of carbon fiber and resin mixture at the bonding area.Based on the morphology and shear force of TC4/CFRTP joints,the optimal process parameters are as follow: 850 W for laser power,+6mm for defocus distance,0.8m/min for laser scanning speed and the shear force of joint was about 1023 N in this joining process parameter case.Subsequently,surface texture and micro-arc oxidation/silane coupling agent processes were adopted to improve surface state of TC4.Strengthening mechanisms of TC4/CFRTP laser joining joints under physics or chemistry scale were elucidated.The results showed that,surface texture improved the adsorption capacity of molten CFRTP on TC4 surface,which promote the interfacial mechanical interlocking and the formation of Ti-C?Ti-O and other new chemical bonds.The maximum shear force of TC4/CFRTP joints could enhance to 2621 N,which increased by approximately156% compared with untreated case.Micro-arc oxidation process could not only improve the chemical state of TC4 substrate surface but also adsorb more functional group hydroxyl(-OH)on TC4 surface,which could promote the introduction of functional group amino(-N-H)induced by silane coupling agent treatment.The hydrogen bond joining generated at the joining interface between amino group(-NH)and the internal functional group carbonyl group(C=O,R-CO-R)and ether bond(R-O-R)of CFRTP,which promoted the joining strength further enhanced under the condition of interfacial high temperature.Finally,multiple processes of surface texture and micro-arc oxidation/silane coupling agent treatment was applied in TC4 surface and the dual scale reinforcement mechanism was discussed.The response surface method was employed to design surface morphology parameters of TC4 substrate.The optimal surface morphology parameters are as follow: 0.3mm for texture grid width,100?m for texture depth and2 min for micro-arc oxidation time.The results suggested that multiple processes of surface texture and micro-arc oxidation/silane coupling agent treatment could facilitate interfacial physical mechanical interlocking in texture grid and micro-arc oxidation porous structure,alleviate stress concentration and further accelerate chemical bonding and hydrogen bond joining between functional groups.The dual scale reinforcement of joining interface could intensify shear force of TC4/CFRTP joining joints to 2901.4N,increased by approximately 183% compared with untreated case,further improvement of interface joining strength was thus realized. |
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