Ultrahigh bonding strength and excellent corrosion resistance of Al-TPU hybrid induced by microstructures and silane layer

Abstract

• Anodizing to obtain porous oxide layers. • Coupling agent treatment improves hydrophobicity. • Silane layer improves bonding strength. • Influence of coupling agent self-assembly times on aluminum alloy surface. Lightweight damping hybrids play a vital role in application of aerospace, traffic vehicle and precision machining. The fabrication of such multifunctional structures is very challenging. Aluminum alloy (Al) - thermoplastic urethane (TPU) hybrids with ultrahigh bonding strength were manufactured by direct injection joining process. After pretreating the Al surface with anodization, a porous oxide film with a pore diameter of 40–70 nm and a porosity of 25.5 % was formed. The 6-(3-triethoxysilylpropyl) amino-1,3,5-triazine-2,4-dithiol monosodium salt was used to further improve the bonding strength of Al - TPU hybrids. It revealed that when the Al was treated by silane coupling agent for two times, the bonding strength reaches 17 MPa, improving by 37.1 % compared with untreated sample. Besides, the failure mode was TPU failure rather than interface failure. Furthermore, the hybrids exhibit excellent corrosion resistance when subjected to NaCl solution. The bonding strength of Al-TPU hybrids decreases by only 8% after the corrosion test, which is much lower than that of the common hybrids fabricated without the silane agent (reduced by 36 %). These results proved that the silane layer with double sulfhydryl groups (-SH) formed on the Al surface played vital role on bonding strength and corrosion resistance of the Al-TPU hybrids.