Study On Ultrasound-assisted Press Molding Of Polypropylene/Aluminum Alloy And Micro-nano Interface Bonding Mechanism

With the energy crisis and environmental pollution becoming increasingly prominent,the application of lightweight materials has become one of the important means of energy saving and emission reduction technology,especially in the automotive,electronic and other industrial fields.Among them,polymer/metal hybrid materials?PMH?can not only meet the comprehensive performance requirements of automobile and electronic products,but also significantly reduce the weight of products.Therefore,the research of polymer metal composite molding technology is especially important.In this paper,isotactic polypropylene/aluminum alloy materials without adhesive were prepared by ultrasonic assisted press forming technology,and the adhesive properties and mechanism of the products were studied.Firstly,the micro nano porous oxide film was developed under the surface of aluminum alloy by the constant current method of phosphoric acid anodizing.Secondly,the effects of molding temperature,pressure,ultrasonic amplitude and ultrasonic time on the bonding properties of the products were examined by orthogonal test,and the best molding process parameters were obtained.Finally,bonding properties of polypropylene/aluminum alloy products formed by conventional pressing and ultrasonic assisted pressing were compared,and the mechanism of interface bonding enhancement by ultrasonic assisted heterojunction technology was summarized.1.Preparation of micro nano porous aluminum alloy surface via anodizingIn order to obtain a suitable micro interlock structure,the surface of A5754aluminum alloy was treated by polishing and constant current phosphoric acid anodizing respectively.The results of SEM and AFM show that the surface of polished P-Al was smooth without obvious micropores and defects,and the roughness was only 2.318nm.The honeycomb porous film was formed on the surface of aluminum alloy after anodizing with phosphoric acid:the porosity of P/A¹-Al with a current density of 4A/dm²was 44.72%,and the average aperture was 180nm,and the roughness was 58.346nm.When the current density increased to 16A/dm²,the porosity and average pore size of P/A²-Al were 41.94%and 130nm respectively,and the roughness reached 89.951nm.2.Optimization of ultrasonic assisted pressing process of isotactic polypropylene/aluminum alloy through orthogonal experimentThe P/A²-Al sample with current density of 16A/dm²was selected as the experimental sample to investigate the influence of four parameters?amplitude,ultrasonic time,pressure,bonding temperature?of ultrasonic pressing on the properties of polypropylene/aluminum alloy composite.The L₉?3⁴?orthogonal experiment showed that pressure and bonding temperature have a great influence on the tensile shear strength of the sample,while ultrasonic time has a great influence on the elongation at break and bending property of the sample.The optimum processing parameters of ultrasonic assisted pressing were:amplitude 50%,ultrasonic time 5s,pressure 0.6MPa,bonding temperature 175?,pressing time 15s.3.Study on the bonding mechanism of polypropylene/aluminum alloy lap interfaceIn order to explore the bonding mechanism of ultrasonic assisted heterojunction technology,the bonding properties of polypropylene and different current density phosphoric acid anodized aluminum alloy lapping samples were compared and analyzed under the condition of non ultrasonic and ultrasonic assisted.The experimental results showed that the tensile shear strength of the HPT-1 sample was9.21±0.80MPa,while that of the UHPT-1 sample was 19.08±0.18MPa,which is107%higher than that of the non ultrasonic samples.When the anodizing current density increased to 16A/dm²,the tensile shear strength of the HPT-2 sample was11.51±0.91MPa,24%higher than that of the HPT-1 sample,while that of the UHPT-2 sample was 23.98±0.56MPa,108%and 25%higher than that of the HPT-2and UHPT-1 samples.The failure interface of the sample was characterized by SEM.The results showed that the surface of the HPT-1 sample was flat and the failure mode is mainly interface debonding.When the current density of anodizing increases,the failure mode of the HPT-2 sample was interface failure+cohesion failure,the resin residue on the surface of aluminum alloy increases,and there was no obvious plastic deformation on the surface of polypropylene.Although the failure modes of the UHPT-1 and UHPT-2 samples were interface failure+cohesive failure,and obvious plastic deformation appears on the surface of polypropylene after failure,the area of plastic deformation on the surface of the UHPT-2 sample was larger and the plastic deformation was more obvious.The results of electron microscopy and linear scanning showed that there were small gaps in the cross section of the HPT-1 sample,and there was no obvious element diffusion between polypropylene and aluminum alloy,but the HPT-2 sample showed obvious element diffusion at the cross section.UHPT-1 and UHPT-2 samples showed that the polypropylene melt entered into the nanopore and formed mechanical interlock structure at the interface,and the interface bonding was very tight,and the line scanning showed that there was obvious element diffusion.The results of X-ray diffraction?XRD?and differential scanning calorimetry?DSC?showed that?crystal of polypropylene appeared at the interface of UHPT-1 and UHPT-2 samples,while?Crystal appeared at the interface of conventional samples.