Effects of salt spray on the mechanical properties of aluminum-epoxy adhesive joints

The aluminum bonding joints were aged in salt spray fog for various aging time from 0 to 1200 h. Uniaxial tensile tests were conducted for the joints to obtain the residual strength of the joints. The test results showed that the residual strength of the joints increases firstly and then decreases with the aging time in salt spray environment. The mechanism of the spray fog environment effect on the joint residual strength is analyzed by infrared spectral analysis and energy dispersive spectroscopy experiments. It is suggested the effect of aging time in the salt spray fog on the joint residual strength is the competing result of two mechanisms. One positive mechanism is that the adhesive expands after absorbing water in the early aging and reaches its saturation after a certain time, which leads to releasing of the internal stress in joints and consequently increases the joint residual strength. Another negative mechanism is that the water molecules permeating into the adhesive when aged in salt spray fog leads to the plasticization of the adhesive, which results in decreasing the joint residual strength as the aging time increases.