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Прегледај по Аутор "Milčić, Miodrag"

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Comparison between Mechanical Properties and Joint Performance of AA 2024-T351 Aluminum Alloy Welded by Friction Stir Welding, Metal Inert Gas and Tungsten Inert Gas Processes
(MDPI, 2024-07-05) Milčić, Miodrag; Klobčar, Damjan; Milčić, Dragan; Zdravković, Nataša; Ðurić, Aleksija; Vuherer, Tomaž
The aim of this work is to study joining Al 2024-T3 alloy plates with different welding procedures. Aluminum alloy AA 2024-T351 is especially used in the aerospace industry. Aluminum plates are welded by the TIG and MIG fusion welding process, as well as by the solid-state welding process, friction stir welding (FSW), which has recently become very important in aluminum and alloy welding. For welding AA2024-T35 with MIG and TIG fusion processes, the filler material ER 4043—AlSi5 was chosen because of reduced cracking. Different methods were used to evaluate the quality of the produced joints, including macro- and microstructure evaluation, in addition to hardness and tensile tests. The ultimate tensile strength (UTS) of the FSW sample was found to be 80% higher than that of MIG and TIG samples. The average hardness value of the weld zone of metal for the MIG- and TIG-produced AA2024-T3511 butt joints showed a significant decrease compared to the hardness of the base metal AA2024-T351 by 50%, while for FSW joints, in the nugget zone, the hardness is about 10% lower relative to the base metal AA2024-T3511.
Comparison between Mechanical Properties and Joint Performance of AA 2024-T351 Aluminum AlloyWelded by Friction Stir Welding, Metal Inert Gas and Tungsten Inert Gas Processes
(MDPI, 2024) Milčić, Miodrag; Klobčar, Damjan; Milčić, Dragan; Zdravković, Nataša; Ðurić, Aleksija; Vuherer, Tomaž
The aim of this work is to study joining Al 2024-T3 alloy plates with different welding procedures. Aluminum alloy AA 2024-T351 is especially used in the aerospace industry. Aluminum plates are welded by the TIG and MIG fusion welding process, as well as by the solid-state welding process, friction stir welding (FSW), which has recently become very important in aluminum and alloy welding. For welding AA2024-T35 with MIG and TIG fusion processes, the filler material ER 4043—AlSi5 was chosen because of reduced cracking. Different methods were used to evaluate the quality of the produced joints, including macro- and microstructure evaluation, in addition to hardness and tensile tests. The ultimate tensile strength (UTS) of the FSW sample was found to be 80% higher than that of MIG and TIG samples. The average hardness value of the weld zone of metal for the MIG- and TIG-produced AA2024-T3511 butt joints showed a significant decrease compared to the hardness of the base metal AA2024-T351 by 50%, while for FSW joints, in the nugget zone, the hardness is about 10% lower relative to the base metal AA2024-T3511.
DISSIMILAR WELDING OF ALUMINUM ALLOYS 2024 T351 AND 6082 T6 BY TIG PROCESS
(Sveučilište u Slavonskom Brodu, Strojarski fakultet, Društvo za tehniku zavarivanja Slavonski Brod, 2023) Milčić, Dragan; Milčić, Miodrag; Vuherer, Tomaž; Đurić, Aleksija; Mitić, Dragan; Radovanović, Andreja
The aim of this work is to study the metallurgical and mechanical properties of dissimilar assemblies of 2024 T351 and 6082 T6 aluminum alloy by the TIG process. Aluminum alloy 6082 T6 is well weldable by classical fusion welding processes (MIG and TIG), while aluminum alloy 2024-T351 is almost non-weldable. Base metals were sheets with a thickness of 8 mm. The assembly of the plates was carried out by filler wire of an aluminum alloy type 4043A (AlSi5) with 2 mm of diameter. For the welding of these two Al alloys by TIG welding process in argon a shielding gas. The microstructural evolution across the welded joint dissimilar AA6082-T6 to AA2024-T351 aluminum alloy was characterized using optical and scanning electron microscopy (SEM). The hardness welded joint is the smallest in the melted area and the biggest on the side of 2024 alloy in HAZ. The fracture surface section of the tensile specimen is in the HAZ zone on the BM side - 6082-T6. The tensile strength of the welded joint is 166 MPa compared to 310 MPa for alloy 6082-T6 which is a weaker welded joint material, i.e. the reduction is about two times.
Influence of Surface Preparation of Aluminum Alloy AW-5754 and Stainless Steel X5CRNI18-10 on the Properties of Bonded Joints
(MDPI, 2024) Zdravković, Nataša; Klobčar, Damjan; Milčić, Dragan; Zupančić, Matevž; Žužek, Borut; Milčić, Miodrag; Ðurić, Aleksija
Adhesive bonding has proven to be a reliable method of joining materials, and the development of new adhesives has made it possible to use bonding in a variety of applications. This article addresses the challenges of bonding metals such as the aluminum alloy EN AW-5754 and the stainless steel X5CrNi18-10. In this study, the effects of laser cleaning and texturing on the surface properties and strength of two bonded joints were investigated and compared with mechanical preparation (hand sanding with Scotch-Brite and P180 sandpaper). The bonded joints were tested with three different epoxy adhesives. During the tests, the adhesion properties of the bonded surface were determined by measuring the contact angle and assessing the wettability, the surface roughness parameters for the different surface preparations, and the mechanical properties (tensile lap-shear strength). Based on the strength test results, it was found that bonded joints made of stainless steel had 16% to 40% higher strength than aluminum alloys when using the same adhesive and surface preparation. Laser cleaning resulted in maximum shear strength of the aluminum alloy bond, while the most suitable surface preparation for both materials was preparation with P180 sandpaper for all adhesives.
Influence of Surface Preparation of Aluminum Alloy AW-5754 and Stainless Steel X5CRNI18-10 on the Properties of Bonded Joints
(MDPI, 2024) Zdravković, Nataša; Klobčar, Damjan; Milčić, Dragan; Zupančić, Matevž; Žužek, Borut; Milčić, Miodrag; Ðurić, Aleksija
Adhesive bonding has proven to be a reliable method of joining materials, and the development of new adhesives has made it possible to use bonding in a variety of applications. This article addresses the challenges of bonding metals such as the aluminum alloy EN AW-5754 and the stainless steel X5CrNi18-10. In this study, the effects of laser cleaning and texturing on the surface properties and strength of two bonded joints were investigated and compared with mechanical preparation (hand sanding with Scotch-Brite and P180 sandpaper). The bonded joints were tested with three different epoxy adhesives. During the tests, the adhesion properties of the bonded surface were determined by measuring the contact angle and assessing the wettability, the surface roughness parameters for the different surface preparations, and the mechanical properties (tensile lap-shear strength). Based on the strength test results, it was found that bonded joints made of stainless steel had 16% to 40% higher strength than aluminum alloys when using the same adhesive and surface preparation. Laser cleaning resulted in maximum shear strength of the aluminum alloy bond, while the most suitable surface preparation for both materials was preparation with P180 sandpaper for all adhesives.
Influence of Welding Speed on Fracture Toughness of Friction StirWelded AA2024-T351 Joints
(MDPI, 2021) Milčić, Miodrag; Miličić, Dragan; Vuherer, Tomaž; Radović, Ljubica; Radisavljević, Igor; Đurić, Aleksija
In order to ensure a quality welded joint, and thus safe operation and high reliability of the welded part or structure achieved by friction stir welding, it is necessary to select the optimal welding parameters. The parameters of friction stir welding significantly affect the structure of the welded joint, and thus the mechanical properties of the welded joint. Investigation of the influence of friction stir welding parameters was performed on 6-mm thick plates of aluminum alloy AA2024 T351. The quality of the welded joint is predominantly influenced by the tool rotation speed n and the welding speed v. In this research, constant tool rotation speed was adopted n = 750 rpm, and the welding speed was varied (v = 73, 116 and 150 mm/min). By the visual method and radiographic examination, imperfections of the face and roots of the welded specimens were not found. This paper presents the performed experimental tests of the macro and microstructure of welded joints, followed by tests of micro hardness and fracture behavior of Friction StirWelded AA2024-T351 joints. It can be concluded that the welding speed of v = 116 mm/min is favorable with regard to the fracture behavior of the analysed FSW-joint.
KARAKTERIZACIJA ZAVARENIH SPOJEVA SA DELIMIČNOM PENETRACIJOM NA KONSTRUKCIONOM ČELIKU S355N
(DUZS - Društvo za unapređivanje zavarivanja u Srbiji, Beograd, 2021) Milčić, Dragan; Mitić, Dragan; Radović, Nenad; Milčić, Miodrag; Đurić, Aleksija; Antić, Milica
Postojeći standardi zahtevaju zavarene spojeve sa potpunom penetracijom. Smatra se, da se zavarenim spojevima sa potpunom penetracijom, minimizira koncentracija napona u korenskom prolazu. Međutim, brojne su situacije u industriji, u kojima je zadovoljavajuća nosivost zavarenog spoja sa delimičnom penetracijom. Ako ispitivanja zavarenih spojeva sa delimičnom penetracijom pokažu zadovoljavajuću nosivost, benefiti u odnosu na zavarene spojeve sa potpunom penetracijom se ogledaju u nižim troškovima, odnosno manje je potrebno vreme za pripremu spoja, manje je potrebno dodatnog materijala, odnosno kraće je vreme neophodno za izradu zavarenog spoja. U radu je dato ispitivanje sučeonih zavarivanih spojeva konstrukcionog čelika S355N, sa delimičnom penetracijom, ostvarenih MAG postupkom u nadglavnom položaju (PD) u zaštiti mešavine gasova. Uzorci su zavarivani sa različitim parametrima zavarivanja i sa različitom pripremom spoja – dubina spoja, a ispitivanja su vršena nedestruktivnim metodama (vizuelna kontrola, ispitivanje penetrantima i magnetnim česticama) i destruktivnim metodama –zatezanje, savijanje i tvrdoća.
Microstructure and Fatigue Properties of Resistance Element Welded Joints of DP500 Steel and AW 5754 H22 Aluminum Alloy
(MDPI, 2022-02-14) Đurić, Aleksija; Milčić, Dragan; Burzić, Zijah; Klobočar, Damjan; Milčić, Miodrag; Marković, Biljana; Krstić, Vladislav
The modern concept of lightweight design (LW) requires the application of different materials in one structure (multi-material structures). The structure of different materials has a good perspective for application in the automotive and aerospace industries but only if it is possible to achieve a quality joint between different materials. The most used technology for joining different materials in the automotive industry is Resistance spot welding (RSW). Due to different mechanical, physical, and chemical properties, the joining of different materials by RSW technology does not provide a quality joint, and accordingly, alternative technologies for joining different materials have emerged. Resistance element welding (REW) was developed to enable joint of different materials. This paper presents the welding of AW 5754 H22 Al alloy (1.0 mm-thick) and DP500 steel (1.5 mm-thick) using novel REW. The peak load, absorption energy, microstructure, microhardness and fatigue strength of the REW joint has been investigated. The joint of the same materials has been done also using conventional RSW to compare some results. The results that will be presented in this paper show that that REW can achieve reliable joining of the two materials at relatively low welding currents compared to RSW. Using REW process with a significantly lower welding current, satisfactory mechanical characteristics of the weld joint can be achieved, so peak load is between 2300–2500 N, displacement is between 2.5–3 mm and the absorption energy is between 3.3–5.7 J. REW joints showed fatigue strength with the fatigue limit of 882 N.
Microstructure and Fatigue Properties of Resistance ElementWelded Joints of DP500 Steel and AW 5754 H22 Aluminum Alloy
(MDPI, 2022) Đurić, Aleksija; Milčić, Dragan; Burzić, Zijah; Klobčar, Damjan; Milčić, Miodrag; Marković, Biljana; Krstić, Vladislav
The modern concept of lightweight design (LW) requires the application of different materials in one structure (multi-material structures). The structure of different materials has a good perspective for application in the automotive and aerospace industries but only if it is possible to achieve a quality joint between different materials. The most used technology for joining different materials in the automotive industry is Resistance spot welding (RSW). Due to different mechanical, physical, and chemical properties, the joining of different materials by RSW technology does not provide a quality joint, and accordingly, alternative technologies for joining different materials have emerged. Resistance element welding (REW) was developed to enable joint of different materials. This paper presents the welding of AW 5754 H22 Al alloy (1.0 mm-thick) and DP500 steel (1.5 mm-thick) using novel REW. The peak load, absorption energy, microstructure, microhardness and fatigue strength of the REW joint has been investigated. The joint of the same materials has been done also using conventional RSW to compare some results. The results that will be presented in this paper show that that REW can achieve reliable joining of the two materials at relatively low welding currents compared to RSW. Using REW process with a significantly lower welding current, satisfactory mechanical characteristics of the weld joint can be achieved, so peak load is between 2300–2500 N, displacement is between 2.5–3 mm and the absorption energy is between 3.3–5.7 J. REW joints showed fatigue strength with the fatigue limit of 882 N.
Razvoj elektroventilatora za potrebe automobilske industrije sa aspekta pouzdanosti
(Elektrotehnički fakultet, Univerzitet u Istočnom Sarajevu, 2013) Milčić, Dragan; Živković, Dragoljub; Milčić, Miodrag; Marković, Biljana; Popović, Branislav
Sistem za hlađenje motornog vozila jedan je od najbitnijih sistema za bezbednost i sigurnost motora sa unutrašnjim sagorevanjem (SUS motora), a elektroventilator je ključni podsistem ovog sistema. On obezbeđuje da radna temperatura motora ne pređe dozvoljene granice i da ne dođe do otkaza kompletnog SUS motora, odnosno automobila. Ovaj elektroventilator je ključni podsistem i za klimatizaciju vozila, jer istovremeno hladi hladnjak sistema za klimatizaciju automobila. Elektroventilator se sastoji od DC motora i radnog kola (ventilatora). DC motor je podsistem navedenih sistema koja najviše utiče na bezotkazni rad elektroventilatora, a samim tim i bezotkazni rad sistema za hlađenje motora i sistema za klimatizaciju vozila. Predmet ovog rada je razvoj elektroventilatora sa aspekta pouzdanosti odnosno zahtevanog radnog veka od 3000 časova.
RESISTANCE SPOT WELDING OF STEEL SHEET DP500 - INFLUENCE OF THE WELDING CURRENT ON THE MICROHARDNESS AND WELD NUGGET DIAMETER
(Sveučilište u Slavonskom Brodu, Strojarski fakultet, 2021) Đurić, Aleksija; Milčić, Dragan; Marković, Biljana; Klobčar, Damjan; Milčić, Miodrag; Mitić, Dragan
Dual-Phase steel has been used in body-in-white in order to reduce the weight and enhance the safety of automobiles. One of the most used technology for joining steel in automotive industry is Resistance spot welding. This paper presnet the analysis of the welding current influence on the microhardness and weld nugget diameter. It will be shown in the paper that the increased hardness of the fusion zones reduces the possibility of the necking in the base metal (i. e. Pull-out Fracture - PF mode), which is not considered as a favorable case.Specimens welded with current of 8 kA showed the best mechanical characteristics, the failure load was approximately 20000 N, the hardness of the fusion zone was approximately 350 HV and during the tensile-shear test they faile in PF mode.
TEHNOLOGIJE SPAJANJA LIMOVA OD ČELIKA I LEGURA ALUMINIJA – PREGLED STANJA
(DUZS - Društvo za unapređivanje zavarivanja u Srbiji, Beograd, 2023) Đurić, Aleksija; Milčić, Dragan; Klobčar, Damjan; Marković, Biljana; Milčić, Miodrag
Multimaterijal dizajn je razvijen kao savremeni koncept dizajna za lake konstrukcije (Lightweight design LW) koji ima za cilj integrisanje različitih vrsta materijala u jednu strukturu. Osnovni problem pri spajanju limova od raznorodnih materijala, prvenstveno čelika i legura aluminijuma, su različita mehanička, fizička i hemijska svojstva materijala koji se spajaju. Kroz ovaj rad biće analizirano stanje tehnike kada su u pitanju savremene tehnologije spajanja limova od čelika i legura aluminijuma. Pod pojmom savremene tehnike spajanja misli se na sve inovativne tehnologije spajanje koje su razvijene ili su značajniju primjenu doživjele u posljednjih nekoliko godina.
TENSILE-SHEAR TESTING OF RESISTANCE ELEMENT WELDED JOINT OF CARBON FIBER-REINFORCED POLYMER AND DP500 STEEL
(University of Niš, Faculty of Mechanical Engineering, 2022) Đurić, Aleksija; Milčić, Dragan; Marković, Biljana; Milčić, Miodrag
The aim of the research presented in this paper is to analyze the possibility of joining Carbon Fiber-Reinforced Polymer (CFRP) and DP500 steel using novel joining technology called resistance element welding (REW). These two materials are representatives of the multi-material structure, and in this research 1.0 mm thick CFRP and 1.5 mm thick DP500 steel were used. A S355JR steel rivet was used as the auxiliary element. The specimens were assembled with an overlap distance of 35 mm. The REW joining procedure began by drilling a hole in the CFRP and inserting the 4 mm diameter steel element (S355JR) in the CFRP, after which classical resistance spot welding (RSW) was performed. The tensile-shear tests were done on a Beta 50-7 / 6×14 testing machine at a cross head speed of 2 mm/min. Macrostructural analysis was conducted by using a Keyence VHX-6000 microscope. The results presented in this paper show that resistance element welding can be used for joining CFRP and DP steel.
THE ANALYSIS OF THE OCCURRENCE OF DEFECTS AND DISCONTINUITIES IN THE REW WELD OF DP STEEL AND ALUMINUM ALLOY
(Društvo za tehniku zavarivanja Slavonski Brod, 2023) Đurić, Aleksija; Milčić, Dragan; Klobočar, Damjan; Marković, Biljana; Milčić, Miodrag
Resistance element welding (REW) was developed as an alternative technology for joining dissimilar materials that are difficult to weld with RSW (Resistance spot welding) technology. This technology does not require significant modification of existing equipment in a factory, which is its great advantage. This paper analyzes the occurrence of defects and discontinuities in the REW weld of DP steel and aluminum alloy. Analysis of the macrostructure and analysis of the fractography of the joint were used to detect defects and discontinuities. The following defects and discontinuities are observed: Expulsion of aluminum, asymmetrical spot weld nugget and cracks in the weld area.

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