Study On Interface Structure And Properties Of Plastic/Aluminum Alloy Hybrids Prepared By The Ultrasonicassisted Hot-Pressing Micro-Nano Molding

In recent years,plastics and plastic matrix composites have gradually become important substitutes for metals in automobile,aerospace,shipping,construction and electronic industries.Compared with metal,the mechanical properties of plastics and plastic matrix composites are relatively low,which limits their application under some conditions.Plastic metal hybrid（PMH）is one of the effective solutions to this problem.Through the optimization of the anodizing process,the author obtains the best surface pretreatment process of aluminum alloy,designs orthogonal test optimization,and studies the effects of hot pressing temperature,pressure,ultrasonic amplitude and ultrasonic action time on the connection strength of plastic/metal hot pressing joint,reveals the connection mechanism of plastic/metal composite parts improved by ultrasonic-assisted process,and successfully realizes the integrated molding of plastic/metal.The main experimental conclusions are as follows.The aluminum alloy surface was pretreated by anodizing.The optimum anodizing process parameters are as follows:the electrolyte is phosphoric acid solution with concentration of 100g/L,anodizing temperature is 15℃,oxidation time is 900s,and current density is 4A/dm².Under this parameter,the surface nanopores of aluminum alloy are the largest,the average pore diameter is 163.57 nm,the surface wettability is the best,the contact angle and surface energy are 1.22°and 72.76 m J/m² respectively,and the roughness is the largest.R_a and R_pv are 108.82 nm and 708.48 nm respectively.Based on the optimal process parameters for treating aluminum alloy surfaces,the author designed an orthogonal test to investigate the effects of hot-pressing temperature,pressure,ultrasonic amplitude,and ultrasonic action time on the joint strength of PC/Al hot pressing composite parts.The optimal hot pressing process parameters for PC/Al joints were obtained as follows:hot pressing temperature 260°C,pressure 0.4 MPa,ultrasonic action time 5S,and ultrasonic amplitude 50%.The joint strength was 21.58 MPa under the optimal hot pressing process parameters;the PC/Al composite strength was provided by the micro-nano-mechanical interlocking structure of the composite interface together with the chemical bond（Al-O-C=O）,and the joint strength was positively correlated with the plastic embedding depth of the interface.The embedding depth is about 3.90μm measured by scanning electron microscopy（SEM）under the optimal process parameters;AFM shows that the higher the joint strength of the composite,the higher the R_a and R_pv of the PC surface after the inverse dissolution of Al,with the maximum values of 190 nm and 1000 nm,respectively;the length of the elemental diffusion region on the cross-section of the energy spectrum analysis（EDS）line analysis is 4-5μm.The joint failure of PC/aluminum alloy composite joints is a mixed type of effectiveness:one is the fracture of resin in the nano-pore of aluminum alloy surface,the second is the fracture of aluminum alloy surface oxide layer,and the third is the plastic fracture of the resin matrix.The optimal process parameters for the ultrasonic-assisted hot pressing of PC/ABS/Al composite parts are as follows:hot-pressing temperature 260°C,pressure 0.2MPa,ultrasonic action time 5S,and ultrasonic amplitude 50%.Under the optimum process parameters,the interfacial joint strength was 20.97 MPa,accounting for 33.60%of the plastic matrix strength,which was significantly higher than that of PC/Al.The joint strength of PC/ABS/Al composite parts was mainly provided by the micro-nano mechanical interlocking structure on the joint layer,and the joint strength was positively correlated with the depth of micro-nano pores on the surface of the plastic embedded in the aluminum alloy at the interface.Under the optimal process parameters,the depth of plastic embedding at the interface of the composite part was about 4.50μm as measured by SEM,which was significantly increased compared with the PC/Al joint results;AFM showed that the R_a and R_pv of the PC/ABS surface after the inverse dissolution of Al were 261 nm and 1390 nm,which were increased by 37%and 39%,respectively,compared with the PC/Al composite part joint results;EDS line analysis of the cross-sectional element diffusion X-ray photoelectron spectroscopy（XPS）results show that in addition to the physical riveting structure,there is also a chemical bonding effect in the PC/ABS/Al interface composite layer,and the results of Al2p,C1s and N1s narrow-scan all show that Al-O-C=O chemical bonds are formed at the interface,and the formation of chemical bonds contributes to the strength of the interface connection.No obvious traces of aluminum oxide tearing were observed at the plastic interface after the interface failure,and the failure of the aluminum oxide layer did not occur,probably because the strength of the PC/ABS substrate was lower than that of PC,and the strength of the plastic substrate failed to reach the strength of the oxide layer.