Cleaning and pre-treatment of the surface is an important prerequisite for a high-quality weld and adhesive bond area. The laser process vaporizes dirt particles, oxide layers and other contaminations prior to joining operations. Laser pre-treatment leaves the metallic surface free of contamination and well prepared for welding and bonding. The substrate is not damaged by the laser light. Metallic materials can be "modified" within the upper boundary layer using appropriately intensified laser parameters. This means the surface of the substrate can be enlarged and passivated to match the bonding mechanisms. The passivation of the surface greatly improves the corrosion behavior of light. The substrate is resistant to age and environmental damage. The laser light removes oxide layers including superficial contamination, e.g. from light alloy surfaces. The near-surface zone in the area of typically ～ 1 μm is re-melted within a few nanoseconds, the melt quickly being cooled simultaneously. By dissolving the grain boundaries and due to the heat capacity of the part a "quenching" occurs. This results in a new micro-crystalline amorphous and rough boundary layer (passivation layer) with significantly decreased element corrosion behavior. The modification processes is automatic when exposed to air without any protective gas. The new, passivation oxide layer on top of the melt forms a very stable bond with the adhesive. Combined with the decreasing electro-chemical potential of current aluminum and magnesium alloys this leads to long-term, age-resistant bonds. Short-term re-melting leads to additional micro craters" that cause a significant surface enlargement and thus an increased load transmission particularly under shear load.
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