dubi̇ted Duzce University Journal of Science and Technology 2148-2446 Duzce University 10.29130/dubited.1760460 Resource Technologies Kaynak Teknolojileri CR3 ve Kaplamalı TBF Çelik Sacların Mikro Yapısı ve Mekanik Özellikleri Üzerine Elektrik Direnç Punta Kaynağının Etkileri The Effects of Electric Resistance Spot Welding on the Microstructure and Mechanical Properties of CR3 and Coated TBF Steel Sheets https://orcid.org/0000-0002-5755-5352 Ozturk Yılmaz İmren Beycelik Gestamp Inc, R&D Center 04 19 2026 14 2 340 351 08 08 2025 01 06 2026 Copyright © 2013, Duzce University Journal of Science and Technology 2013 Duzce University Journal of Science and Technology

Bu çalışma, CR3 ve kaplamalı TBF çelik sacların elektrik direnç nokta kaynağı ile birleştirilmesini sunmaktadır. Kaynak parametrelerinin, kaynak bölgesinin makro/mikroyapısı, çekirdek çapı, çökme miktarı ve yük taşıma kapasitesi üzerindeki etkileri, kaynak akımı ve süresi değiştirilerek incelenmiştir. Belirgin bir makro kusur gözlenmemiş, ancak ergime bölgelerinde sınırlı bir karışım görülmüştür. Daha yüksek ısı girdisi karışımı iyileştirmiş ve TBF tarafındaki ısıdan etkilenen bölgeyi (HAZ) genişletmiştir, ancak kaplamadan kaynaklanan sıvı metal gevrekleşmesi (LME) ile ilişkili mikroçatlak riskini de artırmıştır. CR3 tarafında, ergime bölgesine yakın kısımlarda sadece tane irileşmesi gözlemlenmiştir. Isı girdisi arttıkça çekirdek çapı ve çökme miktarı artmış, ancak kaynak dayanımı düşük kalmıştır. Çekme testleri, kırılmaların CR3 tarafındaki HAZ bölgesinde yırtılma şeklinde gerçekleştiğini göstermiştir. TBF tarafında mikroçatlaklar oluşmasına rağmen, daha ince olan CR3 çeliği birleşme dayanımını belirlemiştir.

This study investigates the resistance spot welding behavior of dissimilar low-carbon CR3 steel and coated transformation-induced plasticity-aided bainitic ferrite (TBF) steel sheets widely used in automotive body applications. The effects of welding current (6-7-8-9 kA) and welding time (240–400 ms) on weld microstructure, nugget size, indentation depth, and mechanical performance were systematically examined. Metallographic analysis revealed no macroscopic weld defects; however, limited mixing was observed in the fusion zone, particularly at lower heat inputs. Increasing heat input enhanced material mixing and widened the heat-affected zone (HAZ), especially on the TBF side, but also promoted liquid metal embrittlement (LME)-induced surface microcracks associated with Zn-coating penetration along grain boundaries. The maximum nugget size reached 8.34 mm at 9 kA–400 ms, while the indentation depth remained within automotive acceptance limits, with a maximum value of 21.65%. Tensile-shear tests showed that all fractures occurred in the HAZ of the thinner CR3 sheet in a tearing mode, with a maximum failure load of 4.25 kN at 7 kA–240 ms. Despite the presence of microcracks in the TBF HAZ, the joint strength was governed by the lower-strength CR3 sheet. The results highlight the importance of optimized welding parameters to balance sufficient nugget growth and minimize LME susceptibility in dissimilar advanced high-strength steel (AHSS)–mild steel combinations.

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