Surface Treatment for Improving Durability of Aluminum-Lithium Adhesive-Bonded Joints under Hot-Humid Exposure

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.

Review on the effect of moisture and contamination on the interfacial properties of adhesive joints

“…Surface preparation and different surface treatments were also shown by several authors to play a key role in the water sorption characteristics of an adhesive joint. 69,112,127,128 Sargent 69 determined the effect of the immersion in distilled water at 35 C on adhesive joints with aluminum substrates and phenolic and epoxy-based adhesives for over seven years. The adhesive-adherend combination was found considerably stable even with a significant water concentration, since periodic peel strength tests showed constant joint behavior and no corrosion was found on the substrate.…”

“…Li et al 128 studied SLJs with aluminum-lithium substrates subjected to different surface treatments, analyzing their behavior at a humid environment at high temperature. The surfaces were treated with sandpaper, sandblasting, chemical etching and PAA.…”

Influence of surface treatment on the strength of adhesive joints

“…They showed that the strength of the adhesive joints depends on the type of bonded material. The moderate value of the surface roughness results in a diffusion of moisture, which contributes to the durability of the adhesive joint [28]. Thus, the surface roughening could be applied to certain optimal values, characteristic for a type of material.…”

Recent trend in developing advanced fiber metal laminates reinforced with nanoparticles: A review study

“…Generally, these methods can be categorized into mechanical, chemical, electrochemical, coupling agents, etc. Figure 2 shows the surface morphologies of an Al-Li alloy after surface treatments of sandpaper abrading, sandblasting, chemical etching and phosphoric acid anodizing (PAA) [38]. The use of surface treatment methods, before lamination, can significantly influence the surface morphology, surface energy, wettability and consequently, the mechanical properties of FMLs [27,[39][40][41][42][43][44][45].…”

“…Surface morphologies of Al-Li alloy after surface treatments of (a) sandpaper abrading, (b) sandblasting, (c) chemical etching, and (d) PAA [38]. …”