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Öğe Characterization of the Welding Zone of Automotive Sheets of Different Thickness (DP600 and DP800) Joined by Resistance Spot Welding(Springer India, 2022) Aydin, Kemal; Hidiroglu, Mehtap; Kahraman, NizamettinAutomotive industry in recent years, has gained great importance. In line with this, DP600 and DP800 dual-phase steels and the electrical resistance spot welding method were used in the study. During the experimental trials, different welding currents (6, 7, and 8 kA) were selected and all other welding parameters were kept constant. The effects of the welding parameters on microstructure, hardness, tensile-shear, and cross-tensile strength were analyzed. In the phase measurements, 27.06-29.97% martensite and 70.73-73.85% ferrite phases were found. When the hardness values in the HAZ regions were examined, it was seen that the highest hardness values were 356 +/- 5 HV in the DP600 and 451 +/- 5 HV in the DP800 with a current intensity of 6 kA. Consequently, it was determined that tensile-shear and cross-tensile strengths had increased in parallel with the increase in the welding current and the highest values were determined as 8 kA-15.91 kN in tensile shear and 8 kA-4.91 kN in cross-tensile strength.Öğe The effect of AC and MFDC resistance spot welding technology on mechanical properties of new generation automotive steels(Pamukkale Univ, 2021) Hidiroglu, Mehtap; Kahraman, Unal; Kahraman, NizamettinUsage of UHSS (ultra high-strength steels) had increased in recent years, automobile Body in White-BIW- manufacturers had faced the challenge of choosing between two types of currents for resistance spot welding equipment The objective of this work is to compare the effects ofwelds obtained from both AC and MFDC (alternate current-AC- power source and medium frequency constant current one-MFDC) machines on mechanical performance. Two different welding equipment had been used for making joints between as-delivered 22MnB5 and DP600 steel sheets. The micro-hardness results, tensile shear (TS) and cross tension (CT) tests of resistance spot welded (RSW) joints between as - delivered (22MnB5) and double phase (DP600) steels for both AC and MFDC process are detailed. According to the results, comparatively lower hardness values were observed in the weld metal and heat effected zones of the welded samples obtained by MFDC technology compared to AC technology. The positive effect was observed in the strength and elongation values of the samples welded with MFDC technology according to AC technology. When the CT and TS test results were evaluated, more than 5% improvement is observed on welded samples with MFDC technology. The originality of this paper presents a comparative study of joint performance properties effect for both AC and MFDC process on dissimilar joints between as-delivered 22MnB5 and DP600.Öğe Enhancing weld strength in high-strength steels: the role of regional preheating in RSW(Walter De Gruyter Gmbh, 2024) Aydin, Kemal; Hidiroglu, Mehtap; Kahraman, NizamettinIn this study, automotive in sector use STRENX 700 CR and DP 800 steels were joined by resistance spot welding using medium frequency direct current. Some parts were joined under atmospheric conditions, while others were joined by applying regional preheating to their heat-affected zones before welding. The design, manufacturing, and adaptation of the preheating system to the welding machine were carried out as part of this study, considering it as a new system. After the joining process, nondestructive and destructive tests were performed on resistance spot welding connections between STRENX 700 CR and DP 800 steels. Hardness tests revealed that the preheating applied to the heat-affected zones before welding reduced the hardness of the weld metal by approximately 8 %, while the microstructure analysis showed that the regional preheating increased both the weld metal and the heat-affected zones width. The tensile-shear strength increased by about 7 %, and the cross-tension test strength increased by about 5 % with the preheating applied to the heat-affected zones before welding. In both the tensile-shear and cross-tension tests, all failures occurred in the form of button shearing from the heat-affected zones. The regional preheating treated specimens showed the highest fatigue life, with an average of 947,632 cycles.Öğe AN INVESTIGATION INTO THE JOINING OF TITANIUM WITH COPPER THROUGH DIFFUSION WELDING/BONDING(Gazi Univ, Fac Engineering Architecture, 2013) Aydin, Kemal; Hidiroglu, Mehtap; Kaya, Yakup; Kahraman, NizamettinIn this study, Ti-6Al-4V and copper were joined through different welding temperatures (825 and 850 degrees C) and holding time (15, 30 and 60 min) diffusion welding/bonding method under argon shielding. The welded joints were subjected to hardness and shearing tests in order to determine their interfacial strength. In addition, microstructural properties of the joined interface were examined using optical and scanning electron microscope (SEM). EDS graphs and diffusion maps of the interface were obtained by carrying out line and elemental analyses. The shearing tests revealed that increasing welding temperature and holding time increased the shearing strength of joined parts. The hardness tests indicated that hardness values increased with increasing distance from titanium to the interface and decreased with increasing distance from the interface to the copper. EDS analyses showed that different reaction areas took place in the welded parts depending on the temperature and holding time.Öğe Optimizing Advanced High-Strength Steel Joints via Regional Rapid Cooling in Resistance Spot Welding(Wiley-V C H Verlag Gmbh, 2024) Hidiroglu, Mehtap; Aydin, Kemal; Kahraman, NizamettinDuring resistance spot welding (RSW), the thermal cycles that occur cause microstructural differentiations in the heat-affected zones of martensitic steels, leading to internal stresses. In this context, a new and innovative methodology has been developed to minimize the adverse effects of heterogeneous hardness changes in the welding area on joint durability. This methodology utilizes a unique prototype setup based on the regional rapid cooling (RRC) process, which is integrated into the welding machine and operates in synchronization with the machine during the process. Through this setup, the aim is to effectively control the microstructure and hardness values in the welding area. This innovative approach presents potential improvements in the field of welding technology by aiming to optimize material performance during the welding process. According to microstructure results, the RRC process has narrowed the heat-affected zone to 1.27 mm, increased the hardness values by 9.2%, showed a 3% increase in tensile-shear strength, a 9% increase in cross-tension strength, and based on fatigue strength results, no fractures occurred in all specimens subjected to a force of 0.3 kN. The study introduces a new methodology to control microstructural differentiations and internal stresses in martensitic steels' heat-affected zones during resistance spot welding (RSW). Utilizing a unique prototype setup based on the regional rapid cooling (RRC) process, the method optimizes material performance by narrowing the heat-affected zone, increasing hardness and tensile-shear strength, and preventing fractures under fatigue.image (c) 2024 WILEY-VCH GmbH
