Direct joining of PP-Al5052 hybrid with high bonding strength by two-step anodization treatment and polymer modification

Abstract

Polymer-metal hybrid (PMH) structures with excellent physical and chemical properties are widely required in aerospace, electrical, automotive and many other fields. It is one of the key challenges for the joining operation between the metal and polymer at the interface. In this study, pretreatment on aluminum alloy (Al5052) sheet by two-step anodization and maleic anhydride-grafted polypropylene (PP-g-MAH) were applied to enhance the bonding performance of PMH structures via injection-molded direct joining process. The effects of anodization treatments on the interfacial wettability, surface morphology and tensile strength were investigated. Besides, the bonding mechanism was further analyzed by molecular dynamics (MD) simulation method. Experimental results showed that the hierarchical nanopores and branched structures were formed after the two-step anodization process, which greatly improved the surface wettability. Using oxalic acid solution as the electrolyte in the second anodization, the bonding strength of PP-Al5052 sheet was greatly improved. With PP-g-MAH resin, the bonding strength reached a maximum of 17.54 MPa, resulting in a tensile failure at the PP-g-MAH part itself. MD simulations revealed that the MAH groups contributed to enhancing the interfacial interactions, while the existence of phosphate ions decreased the chemical interactions at the interface.