Microstructures and Mechanical Butt Weld Properties in Dissimilar AA5754-AA3003 Gas Welding Necat ALTINKÖK and Mehmet Emin ASAN

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1 2016 International Conference on Computational Modeling, Simulation and Applied Mathematics (CMSAM 2016) ISBN: Microstructures and Mechanical Butt Weld Properties in Dissimilar AA5754-AA3003 Gas Welding Necat ALTINKÖK and Mehmet Emin ASAN 1 Hendek Vocational School, Sakarya University, Department of Mechanical and Material Technology, Hendek Sakarya, Turkey 2 Hendek Vocational School, Sakarya University, Department of Computer Technology, Hendek Sakarya, Turkey *Corresponding author Keywords: Dissimilar MI-TIG welding, Macrostructure and microstructure, Mechanical properties Abstract. In this study, the effect of double pulsed Metal Inter Gas (MIG) Gas Tungsten Arc Welding (TIG) on metal droplet transfer, weld pool profile, weld bead geometry and mechanical properties of weld joint of Al alloys are presented. Plates of AA5754-AA3003 aluminum alloys were dissimilar welded by ER5356 welding wire. Full penetration joints without any defects were produced. The influences of arc welding parameters on welding speed and weld appearance were studied through macrostructure and microstructure characterization of fusion zone of an AA5754-AA3003 weld joint. The tensile properties and micro-hardness values of welded specimens were measured. Introduction Aluminum alloys are common structural materials for aerospace and automotive constructions used in parts which require their high strength to weight ratio, ductility and recyclability. In particular, the 5000 series Al Mg non heat treatable alloys have deep drawing and sheet forming properties, which make them suitable for automotive tailored blanks [1]. These conventional welding techniques results in coarse-grained and inter metallic regions in the weld zone followed by a prominent heat affected zone (HAZ) and the base material (BM) [2].The commercial 3003 (Al-Mn series) aluminum alloy is broadly utilized as a part of the holder, bundling, and car industry because of its higher quality, consumption resistance and formability. [3]. In the current paper, Al 5754-AA3003 alloys were joined by two welding methods namely Gas Tungsten Arc Welding (TIG) and Metal Inter Gas (MIG) welding in butt joint geometry. The relationship between welding parameters and the mechanical properties like tensile properties, micro-hardness and microstructures are investigated. Experimental Procedures The welded samples were exposed to tensile-test in a KONDI-A X1150 AB type testing machine at room temperature with 1 m/s speed under. Test specimens were prepared according to TS 287 standard. In addition, ER 5356 wire electrode having 1.2 mm diameter was used as filler metal. The spectrometric analysis of the specimens was done via a Beirth Spectrometer and the chemical compositions of both base-metal and wire electrode was given in Table 1. Micro-hardness values of welded Al alloys were obtained by using HMV2 SHIMADZU type machine. An ER5356 filler wire. Table 1. Chemical composition of Al 5754 alloy and ER 5356 wire electrode (wt %). Material Si Fe Cu Mn Mg Cr Zn Ti Al AA Balance AA , Balance Wire electrode Balance

2 GMA welding operations were performed by means of a DAIHEN Model DR Series ARK ROBO 1100 welding robot having a working capacity of A and 0 50 V ranges. The welding opening was fixed as 0.8 mm and the torch was centered. Aluminum is one of the lightest structural metals and joining it presents several challenges. For this reason, gas tungsten arc welding (TIG) has been used to weld Al alloys by using ESAB 4300i welding machine.the constant parameters during welding process: The thickness of base-metal is 2.5 mm, wire electrode diameter is 1.0 mm, protective gas is 82 wt% Ar + 18 wt% CO 2 mixture, nozzle opening is 10 mm, the free wire length is 15 mm wire feeding rate is 12 m/min, arc distance is 3 mm and the torch angle is 5. The variable parameters are; welding current (I) as 105A, arc voltage (V) as 22, 24 and 26 V, the welding speed (S) as 0.6/min selected for the welding experiments. Having finished the welding processes, the specimens were cut perpendicular to welding direction by using a closed circuit saw cooled by boron oil in order to measure the depth of penetration. The cut surfaces were grinded and etched. The macro and micro-structure photos were taken from these etched surfaces by means of a Nikon Stereo Zoom optical microscope in 10x magnification. The penetration measurements were finished from macro-structure photos by using a new vision program. Vickers hardness tests were performed in order to provide some information on the mechanical properties along the weld zone. Micro hardness profiles were done on the cross-section of joints welded at a speed of 0.6 m/min. Results and Discussion Tensile Test Results The tensile test specimens were prepared according to ASTM-E8M standard and these were exposed to tensile test. The yield strength and ultimate tensile strength of AA5754 and AA3003 metals were calculated as 157MPa, 237.1MPa and 124MPa, 159MPa in un-welded original specimens, respectively. Its yield strength values decreases to 128 MPa and 117 MPa in TIG and MIG welded joint of AA 5754-AA3003 sample, respectively. When the neck point is reached (i.e. maximum tensile strength), the strength values increased to 181 MPa and 197 MPa values for, TIG and MIG welded samples, respectively. The fractured tensile test specimens were shown in Figures. 1(a,b) in In Figure. 1 fracture was observed in heat affected zone (HAZ). In Figure. 1, failure was more detrimental than TIG welded one, because the fracture was occurred in between weld zone and HAZ in MIG welded specimen. This proves that the lower strength values of yield strength and ultimate tensile strength values of MIG welded samples than TIG ones. Figure 1. Tensile test fracture surfaces AA 5754-AA3003 MIG weld material TIG weld material. The ultimate tensile strength of TIG welded sample was measured as 197 MPa and the yield strength value was 128 MPa. Small irregular and spherical pores can be detected throughout the specimen section. They located in the bottom side of the weld. The regular fused zone and low macro-porosity that formed.the similar findings were detected by Casalino et. al [4]. Micro-Hardness Measurements The hardness results of joints AA5754-AA303 welded by MIG and TIG methods are shown in Figure 3. The Vickers hardness of the bimetal material was measured across the interface, and theresults are presented in Figure 2. The micro-hardness value varies from 33 to 69 HV 0.1 for base metal (BM) MIG AA5754-AA3003 welded joints, respectively. In TIG welding, this

3 showed up variability between 35 HV 0,1 and 75 HV 0,1. The samples were taken from the BM, HAZ and FZ regions of the bimetal slab. The average values of Vickers hardness were 35 HV 0,1 and 75 HV 0,1 for the 3003 and 5754 alloy, respectively. The average Vickers hardness at the interface was measured to be 52HV 0,1. The Vickers hardness, HV (1 HV = 9.8 MPa), approximately equals 3 times the yield strength [5]. Thus, the interface yield strength is also higher than AA3003 alloy but lower than AA5754 alloy. The improved interface hardness with respect to the AA3003 alloy was attributed to the effect of solution strengthening. The similar findings were detected by [6]. Figure 2. Micro-hardness values of the AA5754-AA3003 alloys the interface in different regions. Macrostructure and Microstructure Appearances The microstructure and especially macrostructure appearances of MIG and TIG welded specimens were investigated by optical microscope in which the penetration was also measured. Bead height and depth of penetration were measured by a new vision program as shown in Fig. 3 (a,b) In the light of macro-structure photos of TIG and MIG welded specimens; reliable bead heights and depth of penetration values were obtained in configurations shown in Fig. 3 and. Depth of penetration varies from 2.91 to 2.94 mm for MIG and TIG welded joints, respectively. Over penetrated specimens were given in Fig. 3. Over-penetration is an unnecessary situation and waste of material, production costs rise. It means weight increase in construction and structure becomes heavier. These are undesired events, so it is essential to prevent from over-penetration. The similar findings were detected by Karadenizet. al [7]. a b Figure 3. AA5754-AA3003 MIG,and TIG welding specimen penetration zone. Figure 4 shows the microstructure in fusion zone of samples welded by MIG. The microstructure was mainly composed of dendrite grains and precipitations distributed at the grain boundaries. When the voltage was raised the fine dendrite grains in fusion zone got more. Thus it can be seen that the amount of the fine grains increased with increase of weld voltage. In other words, the temperature increase adjusted in the MIG can improve the fluidity of the weld pool

4 and inhibit the growth of grains [8]. The microstructure in heat affected zone and base metal is presented in Figure 4. The base metal was rolled with typical deformation texture feature [8] and the grain orientation was paralleled to the rolling direction. However, in heat affected zone, the rolled grains disappeared and the coarse grains emerged obviously (Figure 4(c)). It indicated that the recrystallization occurred close to the fusion zone during welding process. The similar findings were detected by Liu et. al[9].the base material microstructure of the advancing aluminum alloys was shown in Figure 4(d). The grains have an elongated morphology consistent with the rolling process of the plates before welding. (c) (d) Figure 4. AA5754-AA3003 MIG welded specimen, fusion zone (FZ), HAZ-BM boundary, (c) welded specimen HAZ-FZ interface zone, (d) base metal (BM). Figure 5.shows the microstructure of the defect-free joint at different locations a, b, c and d which represent the microstructure of weld zone encoded as FZ (fusion zone), HAZ-BM boundary, heat affected zone (HAZ)-FZ interface and BM (base metal) of the alloy welded by TIG method. Figure 5 shows partial melting at the grain boundaries in the fusion zone near the fusion boundary often associated with liquation cracking in these alloys. Similar findings were presented by Preston[10] et al. In Figure 5, the base metal and HAZ boundary behaved as homogeneous solid solutions, identical to the adjacent HAZ in which dissolution was complete. This was reasonable, as the greatest residual stresses occur in the HAZ, not the weld metal, and the stresses developed are not very sensitive to the (low) hot strength assumed for the solidified weld metal. The predicted stresses and subsequent hardness in the weld metal itself should however be treated with caution. In Figure 5(c), HAZ-FZ interface was given. The grains of aluminum matrix become coarser prior to welding process. The base metal of aluminium alloys was seen in Figure 5(d). The homogeneous grains having less retained stress were produced, because base metal is far away from weld zone and does not affected high heat input. Similar results were evaluated by Preston et. al [10]. (c) (d) Figure 5. AA5754-AA3003 TIG welded specimen, fusion zone (FZ), HAZ-BM boundary, (c) weldedspecimen HAZ-FZ interface zone, (d) base metal (BM).

5 Conclusions The values of ultimate tensile strength of AA5754 and AA3003 alloys are MPa and 202 MPa in TIG welded joint, and are 218 MPa and 211 MPa in MIG welded joint, respectively. The mechanical property values of AA5754 metal samples were better than AA3003. Compared to the AA5754 material, a slight reduction in ultimate tensile strength and elongation were observed. Low tensile properties were obtained most probably due to the porosity. Depth of penetration varies from 2.97 to 2.94 mm for TIG and MIG welded joints, respectively.the hardness values TIG welded joint, and are 59HV and 48HV in MIG welded joint, respectively.tig and MIG welded joints have finer grains at fusion boundary, leading to a higher mechanical property. The microstructure was mainly composed of dendrite grains and precipitations were distributed at the grain boundaries in MIG welded specimens. In TIG samples, the homogeneous grains having less retained stress were produced. References [1] M. Jain, J. Allin, M.J. Bull, Deep drawing characteristics of automotive aluminum alloys. Mater. Sci. Eng. A256 (1998) [2] L. Liu, D. Ren, F. Liu, A review of dissimilar welding techniques for magnesium alloys to aluminum alloys, Mater. 7 (2014) [3] J. Silva, J.M. Costa, A. Loureiro, J.M. Ferreira, Fatigue Behaviour of AA6082-T6 MIG Welded Butt Joints Improved by Friction Stir Processing, Mater. Des. 51 (2014) [4] G. Casalino, M. Mortello, P. Leo, Benyounis K.Y., A.G. Olabi, Study on arc and laser powers in the hybrid welding of AA5754 Al-alloy, Materials and Design 61 (2014) [5] T. Wanga, C. Lianga, Z. Chenb, Y. Zhenga, H. Kanga, W. Wang, Development of an 8090/3003 bimetal slab using a modified direct-chill casting process, J. Mater. Proc. Tech. 214 (2014) [6] P. Kamal, K.P. Surjya, Study of weld joint strength using sensor signals for various torch angles in pulsed MIG welding. CIRP J. Manuf. Sci. Technol. 3 (2010) [7] E. Karadeniz, U. Ozsarac, C. Yildiz, The effect of process parameters on penetration in gas metal arc welding processes, Materials and Design 28 (2007) [8] L. Anhua, T. Xinhua, L. Fenggui, Study on welding process and prosperities of AA5754 Al-alloy welded by double pulsed gas metal arc welding, Materials and Design 50 (2013) [9] F. Liu, Z. Zhang, L. Liu, Microstructure evolution of Al/Mg butt joints welded by gas tungsten arc with Zn filler metal, Mater. Charact. 69(2012) [10] R.V. Preston, H.R. Shercliff, P.J. Withers, S. Smith, Physically-based constitutive modelling of residual stress development in welding of aluminium alloy 2024, Acta Materialia 52 (2004)