Fatigue Properties of Zinc Coated Low Carbon Steel Sheet Joints by the Means of Spot Welding

Year 2024, Volume: 26 Issue: 77, 299 - 306, 27.05.2024

Ahmet Çetkin

https://doi.org/10.21205/deufmd.2024267714

Abstract

EN 10346:2015 DX52D+Z steel is a low-carbon, zinc-coated steel suitable for cold forming, widely used in the automotive industry due to its superior formability despite its low strength. Sheets produced in different sizes and forms are annealed by passing through the continuous galvanizing line after cold rolling. In this study, fatigue properties of these steels which were joined by spot welding with low welding current and high welding cycles, were measured and failure characterization was made, too. Tensile testing was made using a number of lap joints with different parameters and the variation of hardness within the weld area was also investigated. During the fatigue testing, crack initiation and propagation have been experimentally determined. A significant increase in hardness was observed from the base metal to the weld nugget, and the welding process caused a 38% reduction in the strength of the base material due to the heat affect from the joint. In the microhardness test, the highest hardness value was measured in the weld nugget heat affected zone (228.4 HV), and the hardness of the base metal was 169.4 HV. It has been determined that welded joints have infinite life below approximately 20% of the maximum tensile load.

Keywords

Low carbon steel, Spot welding, Low welding current, High welding cycles, Fatigue limit

Supporting Institution

AKÜ BAP

Project Number

18.FEN.BİL.65

Thanks

This work was supported by Afyon Kocatepe University, Scientific Research Projects Coordination Unit (18.FEN.BİL.65) Afyonkarahisar, Turkey.

Çinko Kaplı Düşük Karbonlu Çeliklerin Nokta Kaynak Bağlantılarının Yorulma Özellikleri

Abstract

EN 10346:2015 DX52D+Z, düşük mukavemetine rağmen üstün şekillendirilebilirliği nedeniyle otomotiv endüstrisinde yaygın olarak kullanılan, düşük karbonlu, soğuk şekillendirmeye uygun çinko kaplı bir çeliktir. Farklı ebat ve formlarda üretilen saclar, soğuk haddeleme sonrası sürekli galvanizleme hattından geçirilerek tavlanmaktadır. Bu çalışmada düşük kaynak akımı ve yüksek kaynak çevrimi ile nokta kaynağı ile birleştirilen bu çeliklerin yorulma özellikleri ölçülerek hasar karakterizasyonları da yapılmıştır. Farklı parametrelere sahip bir dizi bindirmeli bağlantı kullanılarak çekme testi yapılmış ve kaynak bölgesindeki sertlik değişimi de incelenmiştir. Yorulma testi sırasında çatlak başlangıcı ve ilerlemesi deneysel olarak belirlenmiştir. Ana metalden kaynak çekirdeğine kadar sertlikte önemli bir artış gözlenmiş ve kaynak işlemi, birleştirmeden gelen ısı etkisinden dolayı ana malzemenin mukavemetinde %38'lik bir azalmaya neden olmuştur. Mikrosertlik testinde en yüksek sertlik değeri kaynak çekirdeğinin ısıdan etkilenen bölgesinde (228.4 HV) ölçülmüştür ve ana metalin sertliği 169.4 HV olmuştur. Kaynaklı bağlantıların maksimum çekme yükünün yaklaşık %20'sinin altında sonsuz ömre sahip olduğu belirlenmiştir.

Keywords

Düşük karbonlu çelik, Nokta kaynağı, Düşük kaynak akımı, Yüksek kaynak döngüleri, Yorulma limiti

Project Number

18.FEN.BİL.65

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