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I. Failure between primer-type adhesives and metals 1 Improper metal surface treatment 1.1 Cause analysis a. Insufficient degree of metal surface treatment: The main purpose of metal surface treatment is to remove rust, grease, dirt, and other substances from the metal surface, thereby creating a clean, dry surface with sufficient roughness that facilitates the penetration and adhesion of the adhesive. If the metal surface is not properly treated, with residual loose oxide layers or an excessively low surface roughness, then for the same coating area, the effective specific surface area of the bonding interface is reduced; as a result, the density of contact points between the metal and the adhesive is lower, and the bonding strength is consequently lower. b、Unclean metal surface: If the metal surface is not cleaned properly or becomes contaminated again after cleaning, resulting in oil stains, impurities, residual cleaning agents, etc. on the surface, this is essentially equivalent to the formation of an interface layer on the metal surface. The interfacial layer not only **reduces the surface free energy of the metal material, causing the contact angle between the adhesive and the metal surface to increase significantly; this in turn reduces the wettability of the adhesive toward the metal surface. It may also fill the voids on the metal surface, thereby reducing the actual contact area between the metal and the adhesive and thus lowering the bonding strength. 1.2 Solutions: a. Treat the metal surface to remove rust and oil, ensuring that the metal bonding surfaces have sufficient roughness. Common methods for metal surface treatment include mechanical methods (such as sandblasting, mechanical grinding, etc.) and chemical methods (such as acid washing, alkali washing, phosphating, surface coating, high-temperature degreasing, etc.). b. In addition, it is also important to ensure that the metal surface is not too rough; if the surface roughness is too high, its irregularities will affect the penetration of the adhesive. Moreover, such a surface tends to absorb gases, leading to discontinuities at the bonding interface, defects, and stress concentration, all of which reduce the bonding strength. The surface roughness should be determined based on the fluidity and wettability of different adhesives. c) Before applying the adhesive, clean the metal surface thoroughly with chemical solvents to remove oils, impurities, etc.; make sure to let it dry and avoid further contamination. Data shows that the cleaner the surface of the metal to be bonded, the smaller the contact angle between the adhesive and the metal surface, and the higher the bonding strength. 2. Improper selection of adhesive. 2.1 Cause analysis: @The viscosity of the adhesive or primer is too high, preventing it from effectively penetrating the metal surface; bubbles form at the metal/adhesive interface, leading to stress concentration around those bubbles. Although B adhesive can effectively penetrate the metal surface, its adhesion to the metal is too low after curing. 2.2 Remedial measures: Select an appropriate adhesive that ensures good wettability on the metal surface, and whose physical and mechanical or chemical interactions with the metal after curing meet the requirements for adhesive strength.