| Nano injection molding is one of polymer and metal composite molding technologies,which combines the advantages of high strength and engineering reliability of metal with the formability of polymer,and is widely used in automotive electronics,medical equipment and aerospace and other fields.In the process of nano injection molding,it is necessary to clean and corrosion the metal substrate to prepare the nano pit structure with honeycomb characteristics.Then,the polymer is filled into the nano pit in the form of graft chain through the injection molding process to form the physical anchor structure and solidified nailing,so as to realize the close connection of the two.In the process of injection molding,the flow and filling form of polymer at the metal interface will have a crucial influence on the interface connection performance.It is of great theoretical significance and engineering value to study the spatial constrained rheological singularity of polymer,the interface wetting,sliding and spreading mode of polymer/substrate during the process of nano injection molding,clarify the influence law of macro parameters on the anchor bolt morphology and bonding strength,and obtain the process control method to achieve reliable interface connection.In this paper,the flow behavior and anchorage mechanism of polymer materials at the interface of metal substrate in the process of nano injection molding are studied.Using polyphenylene sulfide(PPS)and copper(Cu)as experimental materials,a Cu layer with two "V" shaped 1.8 nm× 1.3 nm grooves and three PPS layers with polymerization degree of 20 were constructed,and then a PPS/Cu nanogroove interface model containing a 3 nm vacuum layer was constructed.The flow behavior,diffusion mechanism and anchoring mechanism of polymer at the nanogroove interface were investigated by molecular dynamics simulation experiments.The results show that the PPS macromolecular chains show obvious wall slip along the metal interface during the process of nano injection molding.Due to the drag effect between the adjacent chains,the macromolecular chains show obvious shear distortion and dynamic spreading.The component of injection pressure in the direction of vertical and groove interface determines the bonding strength of PPS/Cu interface.Due to the effect of entangling and internal friction between polymers,the increase of injection pressure is not positively correlated with the filling effect of interface.The larger the interfacial direction component of injection pressure is,the more obvious the shear flow of PPS chain group is,the more obvious the polymer chain orientation deformation and transition is.In the process of nano injection molding,PPS will gradually form anchor points at the Cu nanofluted interface.Once an anchor point is formed,it will be nailed.At the same time,due to the flexibility of macromolecular chains under the shearing force field,mushroom-like point-to-point pinning is produced.In this paper,the influence of melt temperature,injection pressure and other molding parameters on the bonding strength of polymer/metal interface was studied.Using PPS and Al as experimental substrates,Al metal layers with two "V" shaped 3.1nm× 2.3 nm grooves and 30 PPS layers with polymerization degree of 30 were constructed,and then the interface model of PPS/Al nanogrooves containing 3 nm vacuum layer was constructed.The simulation results show that with the increase of melt temperature and injection pressure,the movement of PPS polymer chain is intensified,the adhesion effect of PPS/Al interface is obviously improved,and the filling rate is also increased.When the melt temperature is set between 553 K-593 K,the PPS/Al interface can increase with the increase of filling time,and the increase rate gradually changes from fast to slow.When the injection pressure is set at 66 MPa,the PPS/Al interface can reach the maximum 4860.2 kcal/mol.When the melt temperature is higher than 593 K,the friction and shear deformation of PPS macromolecular chains are increased due to the intensified molecular thermal motion,but the interfacial energy decreases,and the interfacial adhesion effect is not good.The influence of injection molding pressure is similar to that of melt temperature.When the injection molding pressure changes in the range of 60-66 MPa,the interface energy of polymer/metal interface will gradually increase,but too large injection molding pressure will make the interface energy decrease.In general,the optimal process window in this simulation experiment is: melt temperature 593 K,injection pressure 66 MPa.In this paper,the effects of polymer and metal properties on the filling behavior,interfacial adhesion and failure mechanism of nano-injection polymer were investigated.Using Cu,Al with FCC crystal structure and Fe with BCC crystal structure as metal substrates,and using polar material PA6 and non-polar material PPS as polymer materials,two V slots with sizes of 3.1 nm×2.3 nm(Cu and Al)and 3.4nm×2.1 nm(Fe)were constructed,respectively.Molecular dynamics simulation results of 6 polymer/metal interface models with a size of about 10 nm×5 nm×5 nm including3 nm vacuum layer show that: Both polar and non-polar polymer materials show obvious wall slip behavior in nano injection molding.Compared with non-polar PPS,the wall slip effect of polar PA6 materials is more obvious,and the interface energy,filling rate and other data are better.Compared with FCC substrate,Fe matrix with BCC crystal structure has stronger adsorption effect on polymer material,which weakens the sliding behavior of macromolecular chains at Fe nanointerface,stores higher interfacial energy,and has higher interfacial anchor strength.The tensile failure behavior of the related polymer/metal interface also confirms the above conclusion.Fe base interface is stronger,while Cu and Al base interface show poor failure resistance in tensile experiments. |
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