Study On The Interfacial Structure And Properties Of Press-molded Polypropylene/Aluminum Alloy Hybrids

Polymer-metal hybrids,which combine the advantages of both polymers and metals,are one of the choices for preparing reliable,high performance and lightweight macroscopic composites.This paper mainly uses polypropylene and aluminum alloy as the base material.Firstly,mechanical polishing,chemical etching and anodic oxidation were used to pretreat the surface of aluminum alloy.Then the polypropylene/aluminum alloy composites were successfully prepared by traditional hot pressing and ultrasonic assisted hot pressing respectively.By dissolving aluminum alloy method,ultra-thin section technology,X-ray diffraction(XRD),scanning electron microscopy(SEM),X-ray energy spectrum analysis(EDS)and other technologies,the interface structure and properties of press-molded polypropylene/aluminum alloy hybrids were studied and the main research contents are as follows:1.Aluminum alloy surface treatmentFirst of all,the surface of the cut aluminum alloy plate is mechanically polished,and then the polished aluminum alloy surface was washed by HNO3 and Na OH to remove the oxide layer and generate micron scale pits.Finally,through experimental optimization,phosphoric acid was selected as the anodic oxidation electrolyte for constant current anodic oxidation,and the aluminum alloy surface with micro-nano structure morphology was prepared.SEM shows that the surface pore size of anodized aluminum alloy(Al-L1)with current density of 4A/dm2 is 125-145 nm,and the surface is micro-nano pore structure.The surface pore size of 16A/dm2 anodized aluminum alloy(Al-L2)is in the range of 165-185 nm,and the surface presents a micro-needle-like structure.Deionized water contact Angle experiment shows that the contact Angle of anodized aluminum alloy surface is less than that of polished aluminum alloy surface,and the surface has better wettability and can be hot-pressed with polypropylene better.2.Hot pressing polypropylene/aluminum alloy and its interface structure and propertiesThrough orthogonal experiment optimization,the optimal process parameters of polypropylene/aluminum alloy hot pressing were obtained as follows: pressure0.6MPa,mold temperature 185?,pressing time 15 s.The experimental results show that the tensile and shear strength of N/A1-L1 and N/A1-L2 are 9.77 MPa and11.35 MPa,respectively.After the aluminum alloy was dissolved,the SEM showed that the surface of polypropylene was not completely filled with micro-nano structure,which weakened the interfacial strength.Deionized water contact Angle test showed that the polypropylene surface contact angles of N/Al-L1 and N/Al-L2 composites were 98.5° and 108.3°,respectively,which were higher than those of pure polypropylene(94.6°).SEM shows that the interlocking structure between polypropylene and aluminum alloy is formed.The thickness of the bond layer of N/A1-L1 and N/A1-L2 composites is 6.22 um and 6.47 um,respectively.The tensile-shear failure interface shows that the failure mode of the composite is cohesive failure.3.Ultrasonic hot pressing polypropylene/aluminum alloy and its interface structure and propertiesThe ultrasonic pressing process was optimized by orthogonal test.Under the conditions of 0.6MPa pressure,50% amplitude,185? temperature,15 s pressing time and 5s ultrasonic time,the aluminum alloy/polypropylene was hot pressed.The experimental results show that the tensile and shear strength of U/A1-L1 and U/A1-L2 are 18.96 MPa and 19.14 MPa,respectively.After the aluminum alloy was dissolved,the SEM showed that the trapped gas at the polypropylene/aluminum alloy interface was significantly reduced,and the interlocking structure of microscopic "nodules" appeared at the interface.The contact Angle experiment shows that after the reverse dissolution of U/Al-L1 and U/Al-L2 aluminum alloy,the surface contact angles of polypropylene are 129.6° and 136.4°,respectively.SEM shows that the interfacial layer thickness of U/A1-L1 and U/A1-L2 composites is 3.86 um and5.40 um,respectively.XRD showed that the polypropylene surface of the composite interface appeared ?-crystal.The tensile-shear failure interface of the composite is cohesive failure,and the polypropylene failure surface presents serious plastic deformation.In conclusion,the aluminum alloy surface with micro-nano structure was prepared by proper anodic oxidation process,and the hot pressing composite molding with polypropylene was successfully achieved.The interfacial strength of the composite was improved effectively by introducing ultrasonic wave,and the maximum tensile shear strength was increased by 94.1%.The composite interface presents a nodular micro-nano interlocking structure.The interface failure is in the form of cohesive failure,and the polypropylene surface has a large plastic deformation.Ultrasonic hot pressing is more favorable for polypropylene/aluminum alloy direct composite molding.