The purpose of this paper is to systematically investigate the effect of baking temperature on the morphology, thickness, adhesion and corrosion resistance of an organic-inorganic hybrid coating applied to magnesium alloy AZ31B, trying to elucidate the intrinsic curing-temperature-response mechanisms.
A homogeneous organic-inorganic hybrid coating was prepared on magnesium alloy AZ31B using the sol–gel technique with tetraethyl orthosilicate (TEOS), 3-glycidoxypropyltrimethoxy silane (GPTMS) and triethylene tetramine (TETA). The influence of various baking temperatures (80 °C–130 °C) on the coatings were evaluated through scanning electron microscopy (SEM), energy-dispersive spectroscopy (SEM), atomic force microscopy, optical microscopy (OM), X-ray diffraction pattern (XRD), thickness measurements, scratch adhesion tests and electrochemical methods including potentiodynamic polarization and electrochemical impedance spectroscopy.
The hybrid coating was mainly composed of amorphous SiO2. The hybrid coating showed dense microstructure, uniform thickness (∼20 µm) and intimate interfacial adhesion at the baking temperature of 110 °C, and significantly improved the corrosion resistance of the magnesium alloy, reducing the corrosion current density by approximately two orders of magnitude compared to the uncoated substrate. While adhesion gradually deteriorated with increasing temperature, optimal corrosion resistance and adhesion were achieved at 110 °C, where protection efficiency reached (98.5 ± 0.4)%. This is attributed to enhanced cross-linking density and barrier properties, despite the gradual adhesion loss. At higher temperatures (130 °C), microcrack formation due to excessive internal stress led to deteriorated coating integrity and corrosion performance, with protection efficiency dropping to (84.5 ± 1.1)%.
The identified optimal curing temperature (110 °C) provides coating lines with a simple, readily implementable parameter. This process requires no complex compositional modifications, enabling manufacturers to achieve cost-effective production scale-up, reduced energy consumption and enhanced product durability without additional capital investment.
Enhanced corrosion protection extends magnesium component lifespans, reducing material waste and resource consumption. Lightweighting enabled by durable magnesium alloys contributes to lower vehicle emissions and improved energy efficiency, supporting global sustainability goals and environmental protection.
This work elucidates the competing mechanisms between coating densification and adhesion degradation during thermal curing of GPTMS/TEOS/TETA-based hybrid coatings. It reveals that optimal protection at 110 °C is achieved when barrier property enhancement outweighs adhesion loss, prior to microcracking-dominated failure. This work provides a foundational understanding of process–performance relationships, which is essential for designing more complex coating systems.
