Influence of material composition
Purity Requirements: The purity of aluminum foil directly affects the welding quality. For example, 1060 aluminum foil (containing 99.6% aluminum) has stronger plastic deformation ability due to its high purity and low impurities (such as iron and silicon), making it easier to form a strong joint during welding. If the impurity content is too high (such as 3003 aluminum alloy containing manganese), a hard phase will be formed, which will hinder atomic diffusion and lead to increased joint brittleness.
Alloying elements: Adding elements (such as copper and magnesium) may increase strength, but it will reduce ductility and increase the risk of welding cracks.
Influence of surface condition
Oxide layer: The aluminum oxide (AlO) on the surface of the aluminum foil is an insulator. If it is too thick (>10 nm), it will hinder the transmission of ultrasonic energy, leading to poor soldering. It needs to be removed by pickling or mechanical polishing.
Cleanliness: Oil, moisture, or dust can reduce the coefficient of friction, affecting heat generation and plastic deformation. Alcohol or plasma cleaning is required before production to ensure surface cleanliness.
Roughness: Moderately rough surfaces (Ra 0.2–0.8 μm) can increase contact points and improve mechanical interlocking strength; however, excessive roughness may lead to stress concentration and cause cracks.
Other key factors
Thickness uniformity: Uneven aluminum foil thickness (e.g., localized areas <10 μm) is prone to tearing under welding pressure.
Coating effects: If the conductive layer of carbon-coated aluminum foil contains silver, graphite, etc., it may change the interfacial diffusion behavior. Welding parameters need to be adjusted (such as increasing the amplitude) to compensate for the interference of the coating on energy transfer.
Optimization suggestions
Pretreatment: The oxide layer is removed by plasma cleaning or chemical etching to improve surface activity.
Parameter adaptation: High-purity aluminum foil (such as 1060) is suitable for lower welding pressure (0.2–0.3 MPa), while aluminum foil containing impurities requires higher amplitude (>80%) to overcome the resistance of the hard phase.
Summarize
The purity, surface oxide layer thickness, and cleanliness of aluminum foil are the core influencing factors. High-purity, low-oxidation, and clean aluminum foil has better weldability, while impurities or coatings need to be compensated for through process adjustments.
