Otomotiv endüstrisinde kullanılan batarya hücrelerinin lazer kaynağı ile birleştirilmesi ve bağlantıların mekanik-korozyon özelliklerinin incelenmesi

Öz

Otomotiv endüstrisinde elektrikli ve hibrit araçların artan popülaritesi, batarya paketlerinde hızlı ve verimli bir birleştirme sürecini gerekli kılmaktadır. Bu tür bağlantılarda, bataryayı oluşturan pillerin birbirine bağlanmasını ve elektriksel iletimi sağlayan tırnak ve bara malzemelerinin seçiminde kaynaklanabilirlik, mekanik dayanım, ağırlık, elektriksel iletkenlik ile maliyet gibi faktörler önemlidir. Yüksek verimliliği ve kısa çevrim süreleri sayesinde lazer kaynak birleştirme yöntemi, otomotiv sektöründe giderek daha fazla tercih edilen bir bağlantı teknolojisi haline gelmiştir. Bu çalışmada, otomotiv sektöründe kullanılan batarya paketlerindeki pillerin lazer kaynak yöntemiyle birleştirilmesi durumunda korozyonun kaynak bağlantısının mukavemetine olan etkileri çeşitli deneysel yöntemlerle incelenmiştir. Bu amaçla, lityum iyon batarya paketlerindeki silindirik pil kasa malzemesini temsilen Hilumin (nikel kaplı çelik) ve bara malzemesini temsilen saf bakır ve 1050 serisi alüminyum kullanılarak bu malzemeler lazer kaynak yöntemiyle birleştirilmiştir. Daha sonra lazer kaynağı ile birleştirilmiş numunelerin mekanik dayanımları üniversal çekme testi cihazı ile belirlenmiştir. Numunelerin korozyon etkisindeki mekanik dayanımlarını belirlemek için kaynaklı numuneler galvanik korozyona maruz bırakılmıştır. Kaynaklı numunelerin mikroyapıları taramalı elektron mikroskobu kullanılarak incelenmiştir. Bu çalışmada kullanılan malzemelerin korozyon davranışlarını analiz etmek ve malzemelerin galvanik serideki konumlarını belirlemek amacıyla potansiyodinamik polarizasyon eğrileri oluşturulmuştur. Burada alüminyum-çelik ve bakır-çelik malzeme çiftlerinin kaynaklı bağlantılarının galvanik korozyona eğilimli olduğu görülmüştür. Alüminyumun Hilumin ile galvanik çift oluşturduğunda, korozyona karşı daha savunmasız ve eğilimli olduğu belirlenmiştir. Bakır ve Hiluminmalzemelerinin bağlantısında ise, Hilumin bakıra göre daha düşük bir potansiyele sahip olduğundan daha hızlı bir şekilde korozyona uğramıştır. Bütün numunelerde korozyon sonrası çekme-makaslama dayanımında bir azalma gözlemlenmiştir. Kaynak bölgesindeki mikro yapıdaki heterojenlik (Fe, Al, Ni fazlarının karışımı) galvanik korozyon eğilimini artırmıştır. Bu çalışmada otomotiv endüstrisindeki bataryaların üretiminde kullanılan malzemelerin lazer kaynağı ile birleştirilmesi sonrasında korozyona maruz kalınması halinde mekanik dayanımlarının %5-20 oranında azaldığı belirlenmiştir.

Anahtar Kelimeler

• Batarya hücreleri
• Lazer kaynağı
• Korozyon
• Hilumin
• Alüminyum
• Bakır

Laser welding of battery cells used in the automotive industry and investigation of the mechanical and corrosion properties of the joints

Öz

The increasing popularity of electric and hybrid vehicles in the automotive industry necessitates a fast and efficient joining process in battery packs. In such connections, factors such as weldability, mechanical strength, weight, electrical conductivity and cost are decisive in the selection of the tab and busbar materials that provide the join of the cells forming the battery to each other and electrical conduction. Thanks to its high efficiency and short cycle times, the laser welding joining method has become an increasingly preferred connection technology in the automotive sector. In this study, the effects of corrosion on the strength of the welded connection in the case of joining the cells in the battery packs used in the automotive industry by laser welding were investigated with various experimental methods. For this purpose, Hilumin (nickel-plated steel) representing the cylindrical battery case material in lithium-ion battery packs and pure copper and 1050 series aluminum representing the busbar material were used to join these materials by laser welding method. Then, the mechanical strengths of the samples joined by laser welding were determined by universal tensile testing machine. In order to determine the mechanical strengths of the samples under the effect of corrosion, the welded samples were exposed to galvanic corrosion. The microstructures of the welded samples were examined using scanning electron microscopy. In this study, potentiodynamic polarization curves were created in order to analyze the corrosion behavior of the materials used and to determine the positions of the materials in the galvanic series. Here, it was observed that the welded joints of aluminum-steel and copper-steel material pairs were prone to galvanic corrosion. It was determined that aluminum was more vulnerable and prone to corrosion when it formed a galvanic pair with Hilumin. In the joint of copper and Hilumin materials, Hilumin corroded more rapidly since it had a lower potential than copper. A decrease in tensile shear strength was observed in all samples after corrosion. The heterogeneity in the microstructure in the weld zone (mixture of Fe, Al, Ni phases) increased the tendency to galvanic corrosion. This study determined that when materials used in the production of batteries in the automotive industry are joined by laser welding and then exposed to corrosion, their mechanical strength decreases by 5-20%.

Anahtar Kelimeler

• Battery cells
• Laser welding
• Corrosion
• Hilumin
• Aluminum
• Copper

Kaynakça

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