This study investigated the degree to which adhesion durability in warm water environments is impacted by physical factors such as the initial adhesion strength and chemical factors such as high-corrosion-resistant surface treatment. From a comparison of the initial strength and the relative adhesive strength after the immersion test, it was found that the laser-treated samples exhibited the highest strength. The change in the strength of the interface between the adhesive bond and the aluminum surface during the immersion test could significantly affect the water resistance of the adhesion.

In order to fabricate multi-materials such as joining between aluminum alloy and engineering plastics for the purpose of lightening the weight of automobiles, this study investigated surface treatments to improve the adhesion and corrosion resistance of A5052 aluminum alloy. The two-step anodizing process of phosphoric acid anodizing ＋ sulfuric acid formed a two-layer film with a phosphoric acid treated film on the upper layer and a sulfuric acid treated film on the lower layer. In this two-layer coating, the sulfuric acid-treated film on the lower layer improves the corrosion resistance, and the phosphoric acid-treated film on the upper layer improves adhesion, showing excellent adhesion and corrosion resistance.

We focused a low-power atmospheric pressure plasma jet (APPJ) on a specimen of anodized A5052 aluminum alloy with degraded surface wettability due to atmospheric exposure for more than 30 days. We show that an APPJ driven at about 10 W of power can restore surface wettability. To demonstrate this, specimens were irradiated with an APPJ using He as the carrier gas at a scanning pitch of 1 mm, a scanning speed of 10 mm/s, and a working distance of 20 mm between the glass tube and the specimen surface. Compared to the sample immediately after anodizing, the irradiated surface was found to have equivalent hydrophilicity, 88% of the fracture load in the tensile shear test, and 2% change from X-ray photoelectron spectroscopy (XPS) analysis of C and O on the specimen surface. Thus, short APPJ irradiation is effective in enhancing the surface wettability of specimens that have been exposed for more than 30 days from anodization. Furthermore, the surface modification technique attempted in this study can be applied to a wide range of multi-materials to enable the joining of dissimilar materials.

Research is progressing on multi-material car bodies that take advantage of the features of various structural materials with the aim of reducing the weight of cars. To achieve this, there is an increasing need for dissimilar material joining between aluminum alloy and steel plate. It is known that the joint strength of aluminum alloy/steel plate friction stir spot welding depends on the tool insertion amount (aluminum remaining thickness). Therefore, in this study, instead of the conventionally common load-controlled welding equipment, position-controlled welding equipment that can precisely control the amount and speed of tool insertion used, and the effects of welding parameters and steel plate plating on joint strength investigated. As a result, the relationship between tensile shear strength and aluminum remaining thickness can be approximated by an upwardly convex quadratic curve, and by controlling the aluminum remaining thickness, the tensile shear strength exceeded JIS Z3140 aluminum alloy resistance spot welding A grade. From the above, it is believed that this joining technology has the potential to be applied to vehicle body frame members that require strength.