| Nano injection molding technology has become one of the key directions in the field of metal/polymer composite molding because of its reliable process,high molding efficiency,and various beautiful,compact and lightweight products with excellent performance.The focus of this technology is the surface nano treatment of metal substrate,which can make micro-nano level pits distributed on the surface of the substrate.The molten polymer is filled the micro-nano pits on the surface of the substrate through the injection molding process,and the polymer fills the surface pits through injection molding process and forms a tenon like structure to realize the close combination of the two materials.However,the surface nano treatment commonly used at present leads to the irregular shape,random distribution,and difficulty of precise control of the size of the surface pits.Therefore,in this paper,the surface of 6063 aluminum alloy substrate was nano treated by two-step anodizing method,and the porous structure of oxide film with adjustable pore size and high degree of regular arrangement was obtained.Then,6063 aluminum alloy was anodized in different electrolytes in turn to prepare a double-layer oxide film porous structure with delamination in pore size.Finally,molecular dynamics simulations were carried out to study the effect of different types of porous structures on the interfacial adhesion and bonding properties of metal/polymer.Under the condition of low aluminum purity and normal temperature,the porous structure of anodic oxide film with relatively concentrated and uniform pore diameter and high degree of regular arrangement is prepared on the surface of 6063 aluminum alloy,which puts forward a low-cost and macro preparation method for the orderly nano treatment of metal substrate surface in nano injection molding technology.The main research contents of this paper are as follows:The porous structure of anodic oxide film was prepared on the surface of 6063 aluminum alloy by oxalic acid two-step anodic oxidation method.The effects of anodizing voltage,electrolyte temperature,electrolyte concentration and pore expansion time on the pore size and morphology order of porous structure on anodized film were studied.It was found that Compared with primary anodizing,the pore size of the oxide film obtained by two-step anodizing was uniform,which effectively alleviated the phenomenon of disordered distribution of pore structure and significant pore size difference;the average pore size of the porous structure on the surface of 6063 aluminum alloy increased linearly with the increase of anodizing voltage or pore expansion time in a certain range,and the pore size of the oxide film porous structure was uniform,regularly arranged and honeycomb at 40V;The increase of electrolyte temperature in a certain range had little effect on the pore size and regular arrangement of the porous structure.When the temperature reached 30℃,the oxide film was seriously corroded by the electrolyte,and the adjacent pores were connected or even completely dissolved;Compared with the oxalic acid electrolyte concentration of 0.3mol/L,the electrolyte concentrations of 0.5 and 0.8mol/L had no significant effect on the porous structure of the oxide film prepared by 6063 aluminum alloy.When the concentration is too low(0.1mol/L),the pore diameter of the oxide film was significantly different and the shape was very irregular.The method and growth law of preparing porous structure of double-layer oxide film with layered pore size on 6063 aluminum alloy were studied.The results showed that there were great differences in the porous structure of 6063 aluminum alloy obtained from sulfuric acid and oxalic acid.The pore size of sulfuric acid oxide film was small and the pore density was large,while the pore size of oxalic acid oxide film was large and the pore density was small;the sulfuric acid oxide film covered on the surface of 6063 aluminum alloy led to a longer time to reach a steady state and a lower current density in oxalic acid anodization;After the anodizing of6063 aluminum alloy with sulfuric acid and oxalic acid in turn,the porous structure of double-layer anodic oxide film with small pore size at the top and large pore size at the bottom and obvious pore size stratification was obtained on the surface.The new pores directly initiated at the bottom of the sulfuric acid oxide film and transition to the pore structure of oxalic acid oxide film.Finally,the double-layer oxide film porous structure with the pore structure of sulfuric acid and oxalic acid oxide film was obtained.The non aluminum elements and high temperature in 6063 aluminum alloy led to the porous structure on the oxide film could not be arranged in a hexagonal dense stacking manner,and the nano pores were difficult to show clearly.At the same time,the nano pores on both sides of the voids extended branch pores below it due to the voids caused by non aluminum elements.The effects of different metal surface structures on the bonding behavior and bonding strength of Al/PPS interface were studied by molecular dynamics simulation.The results showed that in nano injection molding,PPS macromolecular chain tended to slide and fill the mold along the side wall of the concave hole of Al substrate.The peripheral PPS macromolecular chain moved down rapidly along the wall due to interface adsorption,and dragged and drove other macromolecular chains to squeeze into the concave hole at the same time;Compared with the cylindrical nano pore structure,although the nano concave hole of the substrate produced extrusion deformation and necking due to the forming pressure at the pore size transition,resulting in the accumulation of PPS macromolecular chains at this place during the filling process,when the polymer macromolecules crossed the necking and entered the concave holes of the lower layer,due to the enlargement of the lower cavity,the PPS material produced mold expansion,improved the filling performance and formed a mechanical lock;Compared with cylindrical nanopores,the extrusion distortion at the pore size transition of stepped nanopores produced crystal defects and disordered lattice structure,resulting in the rise of interface energy.At the same time,this distortion strengthened the mechanical interlocking structure formed after metal and polymer filling,and the injection molded parts could better play the anchor bolt effect. |
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