Multiscale Investigation on the Influence of Aluminum Crystallographic Orientation and Surface Microstructure on Interfacial Bonding Behavior with Polyamide 66

Aluminum/polyamide composites have excellent mechanical properties, good corrosion resistance and light weight, and have a wide range of applications in aerospace and rail transportation, etc. A deep understanding of the interfacial bonding role and mechanism is the key to guiding the research and development design of this type of materials. In this paper, we constructed a cross-scale method to study the interfacial interactions, and systematically explored the interfacial chemical bonding mechanism and the influence of the surface microstructure of metallic aluminum on the interfacial bonding strength in Aluminum/polyamide 66(PA66) composites by adopting the first principles and molecular dynamics methods. Firstly, the adsorption behaviors of PA66 on Al(011), (111) and (200) crystalline surfaces were calculated, and the results of adsorption energies, bond lengths, bond angles and differential charge density analyses indicated that the Al—O and Al—N bonds formed by PA66 on Al(111) crystalline surfaces exhibited optimal interfacial interactions by having stronger bonding stabilities with significant electron transfer. The ionic nature of the Al—O bonds and the covalent nature of the Al—N bonds were further revealed by combining Mulliken charge and fractional wave state density analysis. Subsequently, the effects of five different microstructures of aluminum, namely, planar, ortho-concave, circular-concave, circular-convex and cross-concave, on the interfacial bonding strengths were calculated using molecular dynamics methods. The results show that the ortho-concave structure has the highest interfacial binding energy, which is 25.9% higher than that of the planar surface. In the ortho-concave structure, 15 Å is the optimal depth, too deep leads to the restriction of PA66 penetration and the formation of voids, while too shallow weakens the mechanical interlocking; in the width range of 15~30 Å, the bonding energy increases with the increase of width, and the wide grooves reduce the spatial potential resistance and enhance the interfacial contact. The multiscale simulation method successfully correlates the quantum-scale electronic interactions with the mesoscale structural response, which provides guidance for the interfacial study of metal/polymer composites.