Abstract
The performance of adhesive-bonded joints, which are being increasingly used in the aerospace and automotive industries, under hot-humid conditions remains largely unknown. The effect of surface treatments on the strength durability of aluminum-lithium (Al-Li) alloy adhesive-bonded joints under hot-humid exposure was investigated. Varied surface characteristics were achieved by different mechanical and chemical treatments; combined mechanical and phosphoric acid anodization (PAA) treatments were also used. The adhesive-bonded joints were then exposed to a hot-humid environment. The surface morphology, strength degradation, failure modes, and corrosion resistance of the substrates were analyzed. The results indicated that the combined PAA/mechanical method improved the joint durability under hot-humid exposure. The treated surface, with a roughness of 2.85 μm, exhibited the best durability, losing only 6% of strength after exposure; the failure mode remained cohesive-failure dominant. The durability enhancement was attributed to the porous and moderate rough surface characteristics, which protected the substrate from corrosion and decreased the rate of moisture diffusion from the bonding interface, thereby reducing the degradation of the bonding interface and improving the durability of the joint.
Highlights
In recent years, adhesive-bonded joints have been increasingly used in the aerospace and automotive industries because of their advantage of being lightweight; the bonding techniques used are typically auxiliary methods of mechanical connection or hybrid connection
The joints with different surface characteristics were placed in a hot-humid chamber, at 98%
In strength and the mechanisms of durability improvement surfaceTherefore, treatment the are differences in strength degradation and the mechanisms of durability improvement by and surface analyzed based on the properties of adhesive, the corrosion resistances of the substrates, the treatment are analyzed based on the properties of adhesive, the corrosion resistances of the moisture diffusion along the bonding interfaces
Summary
Adhesive-bonded joints have been increasingly used in the aerospace and automotive industries because of their advantage of being lightweight; the bonding techniques used are typically auxiliary methods of mechanical connection or hybrid connection. In the automotive and aircraft industries, bonded components are typically exposed to moisture and significant temperature changes; it is necessary to study the degradation mechanisms and improve the durability of joints under hot-humid conditions. Investigated the durability of aluminum bonded joints under hygrothermal conditions; they suggested that exposure decreased the joint strength and changed the failure mode, and that substrate corrosion was greatly affected by elevated temperatures. Reported on strength degradation under cyclic moisture exposure using a cohesive zone model, which combined the moisture concentration and infiltration processes Their numerical simulation results indicated that the adhesive moisture distribution significantly affected the failure initiation region of the joint. The effects of different surface treatments on the durability of adhesive-bonded Al-Li joints under hot-humid exposure were investigated. Scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), surface roughness measurements, and polarization corrosion tests were conducted to analyze the mechanism of surface treatments on the degradation of Al-Li bonded joints under hot-humid exposure
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