Strength Properties of Steel/Aluminum Dissimilar Spot Welded Joint
-(Second Report) Investigation of Fatigue Strength-

Ayaka Kagami･Mitsuhiro Aimoto･Eisuke Umeno (Toyota Motor)･Hideaki Matsuoka･Tatsuyuki Amago (Toyota Central R&D Labs.)

In spot welding between steel plate and an aluminum alloy, it is well known that the intermetallic compound formed at the joint interface is closely related to the joint strength. In this study, we fabricated welded joints with protrusion-like structures to overcome the brittleness of intermetallic compounds in spot welding between steel plates and aluminum alloy sheet. We investigate the fatigue strength.

Coaxing Effect in Fatigue of a Stainless Steel Sheet with Stress Raiser

Gyoko Oh (Tokyo Roki)

We investigated the fatigue behavior of stress raisers in stainless steel sheets and clarified the influence of coaxing on the fatigue limit. By observing differences in crack initiation and propagation depending on the stress ratio R and stress amplitude from hysteresis loops and fatigue curves, we attempted to elucidate the mechanisms of crack propagation and fracture. The location and propagation rate of cracks differed depending on the stress amplitude and R value, and it was revealed that coaxing in stress raisers affects fatigue strength and is an important factor influencing crack arrest and fatigue life.

Additively Manufactured HEA for Functional Integration and Weight Reduction in Mobility Systems

Hyomoon Joo (Hyndai Motor)

Recent mobility systems require structural materials with stable properties over wide temperature ranges. Conventional alloys degrade under extreme conditions. A Ni-based high-entropy alloy was fabricated via additive manufacturing, enabling precise microstructural control. The alloy exhibited temperature-insensitive tensile behavior due to its stable single-phase structure and sluggish diffusion. Grain boundary engineering enhanced strain hardening and mechanical robustness. The material shows strong potential for automotive applications, including electric powertrain and thermal components, offering improved durability and reliability for next-generation mobility systems.

A Study on Optimization of Two stage rolling process to Improve formability and Reduce springback of Pure titanium thin sheet for Fuel cell Separator

Jaebong Park･Sunghwan Kim (Hyundai Motor)

It was confirmed to improve the formability and reduce springback of titanium for separators through a two-stage rolling process with intermediate annealing. The effect of rolling texture dispersion due to inducing twin was verified. In addition, the analysis of rolling texture, grain, mechanical properties and springback was conducted based on the number of rolling stage, thickness reduction ratio, final annealing temperature and time. Through these results, the optimal two-stage rolling process that can improve formability and reduce springback were derived.