The objective of research was to determine the weldability, using Tungsten Inert Gas (TIG) of extruded sections made of hard-deformable 5xxx series aluminum alloys with differing magnesium content, i.e. AlMg3, AlMg4,5, AlMg5, AlMg7. Welded joints were obtained as a result of a welding process consisting of several steps. Only welds characterized by very good appearance and quality were selected for tests. As a result of conducted research, TIG welding parameters were determined for sections with a thickness of 8 mm. It was observed that alloys of differing Mg content are characterized by high weldability and do not exhibit a significant reduction of the yield point. Moreover, joints exhibit uniform hardness distribution in the welded joint and heat-affected zone. Tensile strength is reduced

D. Leśniak

H. Dyja

H. Jurczak

J. Borowski

J. Sulej-Chojnacka

English

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461METALURGIJA 55 (2016) 3, 461-464J. BOROWSKI, J. SULEJ-CHOJNACKA, H. JURCZAK, D. LEŚNIAK, H. DYJASUSCEPTIBILITY TESTING FOR WELDING OF AlMg ALLOYS INTENDED FOR EXTRUSIONReceived – Primljeno: 2015-11-03Accepted – Prihvaćeno: 2016-01-30Preliminary Note – Prethodno priopćenjeJ. Borowski, J. Sulej-Chojnacka, H. Jurczak, D. Leśniak, H. Dyja, Met-al Forming Institute, Poznan, Poland The objective of research was to determine the weldability, using Tungsten Inert Gas (TIG) of extruded sections made of hard-deformable 5xxx series aluminum alloys with differing magnesium content, i.e. AlMg3, AlMg4,5, AlMg5, AlMg7. Welded joints were obtained as a result of a welding process consisting of several steps. Only welds character-ized by very good appearance and quality were selected for tests. As a result of conducted research, TIG welding pa-rameters were determined for sections with a thickness of 8 mm. It was observed that alloys of differing Mg content are characterized by high weldability and do not exhibit a significant reduction of the yield point. Moreover, joints exhibit uniform hardness distribution in the welded joint and heat-affected zone. Tensile strength is reduced.Key words: TIG welding, AlMg alloys, parameters of welding, tensile strength, hardness HV01 INTRODUCTIONAluminum alloys, as lightweight materials, are an excellent alternative to steel in many areas of industry. However, the low strength of aluminum alloys limits the extent of their application in industry [1]. This is why research is being conducted on new aluminum al-loys with better mechanical properties in many research centers. Studies show that the addition of Mg in Al al-loys leads to an increase in the strength of hot-formed AlMg alloys [2]. 7xxx series alloys, involving zinc, are among the aluminum alloys with the highest strength, but they have a lower resistance to corrosion than alloys in the 5xxx series. The interest in alloys from this series is mainly the result of their suitability for mechanical processing and welding as well as their resistance to corrosion, which is 2 - 3 times greater than that of 6xxx alloys, which are the most widespread [3].Expansion of the applications of these alloys, par-ticularly in the construction and shipbuilding industries, requires development of methods of joining them that will ensure high strength of joints. Welding of alu-minum alloys was made difficult by problems related to oxide removal and strength reduction in the heat-affect-ed zone. Nevertheless, new welding techniques are solving these problems [4]. Tungsten inert gas welding, or TIG welding, is arc welding using a non-consumable electrode shielded by a neutral gas, and it is the method most commonly used to manufacture structures made of aluminum sections [5].One of the main problems during welding of alu-minum and its alloys is its resulting porosity. Analysis of the gas found inside pores has shown that hydrogen ISSN 0543-5846METABK 55(3) 461-464 (2016)UDC – UDK 621.791.052:669.715.721:620.178.1=111 is the main gas causing porosity. Dissolved gas (H2) that cannot “escape” as the weld congeals forms voids and reduces the strength of the material in the weld and heat-affected zone [6-8].5xxx series alloys have medium strength, and the highest mechanical properties dependent on magnesi-um content reach approx. 300 MPa and are comparable to high AlMgSi alloys [2]. In previous studies did not compare alloys with Mg content from 3 - 7,5 % for sec-tions with thicknesses greater than 2 mm, which is why this problem was investigated in this article in order to determine welding capabilities and the change of me-chanical properties related to this. MATERIALS AND METHODSTests of the weldability of 5xxx series hard-deform-able alloys were conducted by welding sections.Sections were extruded at OML Skawina on a semi-industrial hydraulic press with a pressing force of 5 MN, equipped with a system for measuring the temperature of the metal leaving the die hole. Sections extruded from ingots with a diameter of approx. 100 mm, with four dif-ferent chemical compositions, were tested. In order to investigate the influence of Mg content, alloys with Mg content from 3,5 to 7,14 % were selected (Table 1).Welding of aluminum sections was performed by means of a robotic test station for tungsten inert gas welding (TIG) (Figure 1), in an argon gas shield. The station is equipped with: a welding robot from Pana-sonic (with a touch system for welding wire detection, maximum reach of 1 400 mm, and repeatability of mo-tion ± 0,08 mm), the robot’s welding grip, 300 A TIG welding source, cold wire feeder, uniaxial positioner with a maximum load of  500 kg. An LNT AlMg4,5MnZr 462J. BOROWSKI et al.: SUSCEPTIBILITY TESTING FOR WELDING OF AlMg ALLOYS INTENDED FOR EXTRUSION METALURGIJA 55 (2016) 3, 461-464rod from the Lincoln Electric company, with a diameter of 2,4 mm, was applied during welding tests. When the material was being prepared for welding, sections were chamfered in order to ensure the required weld penetration and to facilitate welding (Figure 1c). Sections were butt welded with the application of pro-cess parameters selected for the arc ignition phase, welding of a curve and straight line, and crater filling. Maximum and minimum intensity of welding current, wire feed rate, and welding rate and frequency were se-lected for every phase of welding.Tensile strength tests were conducted according to standard PN-EN ISO 15614-2 by means of an Instron 4483 strength tester with measuring head, with a max load of 20 kN. Vickers HV 0,1 hardness measurements were performed according to the requirements of stand-ard PN-EN ISO 6507-1:2007. Metallographic speci-mens were etched electrolytically in a 1,77 % HBF4 solution and examined under an Eclipse L150 light mi-croscope (Nikon) with NIS Elements image analysis software.RESULTS AND DISCUSSIONSThe first verification of welded joints was carried out by means of macroscopic tests in order to determine optimal welding parameters. A welding process consist-ing of several steps was developed for further tests, the steps being: arc ignition, welding of a curve (with a spe-cific radius), welding of a straight segment, welding of the second curve, and crater filling (Figure 2). The same procedure was applied to the other side of sections, after samples were rotated by 180 o. In Table 2 selected welding   parameters  are presented.Only welded joints with very good appearance and quality, made using the parameters indicated in Table 2, Table 1  Chemical composition of extruded sections subjected to welding / wt. %AlMg3 AlMg4,5 AlMg5 AlMg7Si 0,224 0,229 0,246 0,235Fe 0,140 0,145 0,146 0,097Cu 0,007 0,004 0,004 0,004Mn 0,465 0,553 0,567 0,580Mg 3,44 4,44 5,54 7,14Cr 0,002 0,120 0,002 0,149Zn 0,002 0,024 0,026 0,026Ti 0,018 0,018 0,019 0,019Al R R R RFigure 1  Test station for TIG welding processes: a) general view, b) welding robot, c) method of material fasteninga)b)c)Figure 2  Diagram of section welding in steps: 1 Arc ignition, holding, 1 - 2 Welding of a curve, 2 - 3 Welding of a straight segment, 3 - 4 Welding of a curve, 4 Crater fillingTable 2  Welding parameters of sections made of AlMg3, AlMg4,5, AlMg5, AlMg7 alloysAlMg3 Imin/ AImax/ AVwire/ m/sHz/ HzVweld/ m/s1 100/ 70 100/70 0,0083/0,0117 3/ 1 0,0083/0,00281 - 2 120 215 0,02 1,2 0,00282 - 3 155 225 0,63 2 0,0043 - 4 35/2065/400,0416/0,0083 1/1,20,33/ 0,2584 20 20 0 0 0AlMg4,5 Imin Imax Vwire Hz Vweld1 100/ 120 100/215 0,0083/0,02 3/1,20,0083/0,0281 - 2 155 225 0,063 2 0,0042 - 3 20 40 0,0083 1,2 0,0333 - 4 20 40 0,0083 1,2 0,02584 20 20 0 0 0AlMg5 Imin Imax Vwire Hz Vweld1 100/100100/125 0,0083 1/1,20,083/0,171 - 2 115 200 0,02 2 0,0042 - 3 155 225 0,033 2 0,0333-4 20 40 0,0083 1,2 0,0334 20 20 0 0 0AlMg7 Imin Imax Vwire Hz Vweld1 100/70100/70 0,083/0,01163/ 1 0,083/0,00281 - 2 115 215 0,02 1,2 0,00282 - 3 155 225 0,063 2 0,0043 - 4 20 40 0,083 1,2 0,0334 20 20 0 0 0463J. BOROWSKI et al.: SUSCEPTIBILITY TESTING FOR WELDING OF AlMg ALLOYS INTENDED FOR EXTRUSIONMETALURGIJA 55 (2016) 3, 461-464were subjected to tensile strength tests. Tensile strength test results of a solid section and a section after the welding process are compiled in Table 3.The strength of solid, extruded sections is dependent on the amount of Mg dissolved in the solid solution. Welded joints broke at the weld for alloys with magne-sium content above 4,5 %. The greater the Mg content, the greater the difference between the strength of the solid section and the welded section. As shown by the authors of paper [1], this may be the result of differing Mg content in the weld and native material, because the process of magnesium evaporation may occur during the welding process.Table 3 Tensile strength of solid sections and welded jointsRm / MPa Rp0,2 / MPaAlMg3 Native material 228 82Weld 223 85AlMg4,5 Native material 291 116Weld 203 109AlMg5 Native material 299 137Weld 163 124AlMg7 Native material 372 179Weld 205 166This is why these differences are so visible at high Mg contents and in sections where the weld is larger, and thus, the welding process is longer. Such a phenom-enon was not observed in the case of welding strips with a thickness of 2 mm, where material was welded in a single step [3]. As shown in Figure 3, there is a lower percentage of strength reduction for yield point than for the Rm parameter – tensile strength. The influence of Mg content can also be seen in the hardness value. HV 0,1 hardness distribution for indi-vidual joints of the alloys subject to analysis is presented in Figure 4 along with an example of indentation posi-tions on the joint of a section made of AlMg4,5 alloy.Hardness tests on the cross-section of welded sam-ples made of alloys with Mg content up to 5 % did not show significant growth or reduction of hardness in re-lation to welding, which was confirmed by offset yield stress results. Such reduction could be observed for the alloy with Mg content above 7 %, which can be ex-plained by mixing of the flux, with 4,5 % Mg content, with the native material and obtainment of greater weld hardness than in the case of other alloys, but with hard-ness lesser than that of the native material. CONCLUSIONParameters of TIG welding of a section with thick-ness of 8 mm were determined as a result of testing of the weldability of sections extruded from 5xxx series alu-minum alloys with Mg content from 3 to 7 %. An auto-matic welding method in successive steps was developed for different current parameters (Figure 1, Table 3). These alloys exhibit high weldability and no signifi-cant reduction of yield point in welded sections. Tensile strength (Rm) is reduced, and the change in strength in-creases as Mg content grows. Such differences were not observed in earlier studies of sections with thickness up to 2 mm [3]. These alloys are also characterized by un-precedented uniformity of hardness distribution in the welded joint, in comparison to 6xxx alloys, and no change in hardness in the heat-affected zone. Sections extruded from 5xxx series aluminum alloys (particu-larly with Mg content above 5 %) have rarely been used in structures until now due to their resistance to defor-mation (hard-deformability). AcknowledgementsResearch was conducted within the framework of a project titled “Development of innovative technology for extrusion of sections from hard-deformable 5xxx se--1001020304050AlMg3 AlMg4,5 AlMg5 AlMg7Rm and Rp0,2/ %Rm(w)/Rm(pw) Rp0,2(w)/Rp0,2(pw)20406080100-12 -8 -4 0 4 8 12Distance from the weld axis/ mmHardness / HV0,1AlMg3 AlMg4,5 AlMg5 AlMg7Figure 3  Percentage change in tensile strength (Rm) and  offset yield stress (R p0,2) of solid sections compared to welded sections Figure 4  Hardness distribution in TIG-welded joint (a) and hardness distribution for AlMg4,5 alloy (b)a)b)464J. BOROWSKI et al.: SUSCEPTIBILITY TESTING FOR WELDING OF AlMg ALLOYS INTENDED FOR EXTRUSION METALURGIJA 55 (2016) 3, 461-464ries aluminum alloys” co-financed by the European Un-ion from the European Regional Development Fund within the framework of the Innovative Economy Op-erational Programme.REFERENCES[1]  D. Yang, Z. Li, D. He, Z. Nie, H. Huang, Microstructural and mechanical property characterization of Er modified Al.-Mg-Mn alloy Tungsten Inert Gas Wells, Materials and Design 34 (2012), 655-659.[2]  D. Leśniak, A. Rękas, W. Libura, J. Zasadziński, Study of the deformability of 5xxx series aluminum alloys with high Mg content in a semi-industrial extrusion process, Obróbka Plastyczna Metali XXV (2014) 3, 159-168.[3]  M.A. Mostafaei, M. Kazeminezhad, Hot deformation be-havior of hot extruded Al-6Mg alloy, Materials Science and Engineering A 535 (2012), 216-221.[4]  B. Guner, E. Kaluc, E. Taban, A. Sik, Mechanical and mi-crostructural properties of robotnic Cold Metal transfer (CMT) 5083-H111 and 6082-T651 aluminium alloys, Ma-terials and Design 54 (2014), 207-211.[5]  Y. Liu, W. Wang, J. Xie, S. Sun, L. Wang, Y. Qian, Y. Meng, Y. Wei, Microstructure and mechanical properties of aluminium 5083 weldments by gas tungsten arc and gas metal arc welding, Materials Science and Engineering A 549 (2012), 7-13.[6] T. Luijendijk, Welding of dissimilar aluminium alloys, Journal of Materials Processing Technology 103 (2000), 29-35.[7]  B. Gungor, E. Kaluc, E. Taban, A. Sik, Mechanical and microstructural properties of robotnic Cold Metal Transfer (CMT) welded 5083-H111 and 6062-T651 aluminium al-loys, Materials and Design 54 (2014), 207-211.[8]  Y. Morisida, H. Furii, F. Inagaki, M. Kamai, Development of high frequency tungsten inert gas welding method, Ma-terials and Design 44 (2013), 12-16.Note:  The responsible translator for english languages is Karol Do-bryniewski, Razut, Poland

Susceptibility testing for welding of AlMg alloys intended for extrusion

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