Abstract
Structural-adhesive-assisted DeltaSpot welding was used to improve the weldability and mechanical properties of dissimilar joints between 6061 aluminum alloy and galvannealed HSLA steel. Evaluation of the spot-weld-bonded surfaces from lap shear tests after long-term exposure to chloride and a humid atmosphere (5% NaCl, 35 °C) indicated that the long-term mechanical reliability of the dissimilar weld in a corrosive environment depends strongly on the adhesive–Al6061 alloy bond strength. Corrosive electrolyte infiltrated the epoxy-based adhesive/Al alloy interface, disrupting the chemical interactions and decreasing the adhesion via anodic undercutting of the Al alloy. Due to localized electrochemical galvanic reactions, the surrounding nugget matrix suffered accelerated anodic dissolution, resulting in an Al6061-T6 alloy plate with degraded adhesive strength and mechanical properties. KrF excimer laser irradiation of the Al alloy before adhesive bonding removed the weakly bonded native oxidic overlayers and altered the substrate topography. This afforded a low electrolyte permeability and prevented adhesive delamination, thereby enhancing the long-term stability of the chemical interactions between the adhesive and Al alloy substrate. The results demonstrate the application of excimer laser irradiation as a simple and environmentally friendly processing technology for robust adhesion and reliable bonding between 6061 aluminum alloy and galvannealed steel.
Highlights
IntroductionSince joining is one of the most important manufacturing technologies, achieving reliable welding between dissimilar high-tensile strength steel and lightweight materials, such as aluminum, magnesium, and fiber-reinforced composites, has become significantly important [6,7,8]
The dissimilar metal weld joint in an overlap configuration suffered from severe galvanic and crevice corrosion in the presence of a corrosive electrolyte
intermetallic compounds (IMCs) reaction layer and gas holes at the interface due to increased joule heating, but the mechanical properties were more favorable than the joint without the adhesive due to the supplementary adhesive bond strength
Summary
Since joining is one of the most important manufacturing technologies, achieving reliable welding between dissimilar high-tensile strength steel and lightweight materials, such as aluminum, magnesium, and fiber-reinforced composites, has become significantly important [6,7,8]. Resistance spot welding has been most employed in metal sheet assembly due to its automation adaptability for high-volume production, superior joint structural performance, and easy control [9,10]. The practical use of fusion-based resistance spot welding between Al alloys and steel has been hampered by difficulties in welding control arising from the large differences in the physical properties of each material, such as low melting temperature and electrical conductivity [11,12,13]. When two dissimilar metals in an overlap configuration come into electrical contact in the presence of a corrosive electrolyte, galvanic and perforation corrosion can become additional major problems that accelerate corrosion of the welded joint [16,17]
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