See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/269573434 Study Fatigue Behavior of Friction Stir Welded Joints for Dissimilar Aluminum Alloys (2024 -T3 and 7020 -T6) ​ Article · February 2014 CITATIONS READS 0 58 1 author: Ahmed Ameed University of Technology, Iraq 7 PUBLICATIONS 3 CITATIONS SEE PROFILE All content following this page was uploaded by Ahmed Ameed on 15 December 2014. The user has requested enhancement of the downloaded file. All in-text references underlined in blue are added to the original document and are linked to publications on ResearchGate, letting you access and read them immediately. Eng. & Tech. Journal , Vol.32,Part (A), No.2, 2014 Study Fatigue Behavior of Friction Stir Welded Joints for Dissimilar Aluminum Alloys (2024 -T3 and 7020 -T6) Dr. Muna K.Abbass Production and Metallurgy Engineering Department, University of Technology/ Baghdad Dr. Ali H. Ataiwi Material Engineering Department, University of Technology/Baghdad E-mail: muke2005@yahoo.com Ahmed Ameed Material Engineering Department, University of Technology/Baghdad Received on: 9/5/2013 & Accepted on 5/9/2013 ABSTRACT The aim of the present work is to investigate the fatigue behavior of friction stir welded joints for dissimilar aluminum alloys (2024 -T3 and 7020-T6). Friction stir welding (FSW) had been done for 6.6 mm thick plate by using NC milling machine with R18 tool steel of 18mm with shoulder diameter and 6mm pin diameter with different tool designs; threaded cone with double bevel, threaded cylinder with concave shoulder of 4°, and beveled cone with concave shoulder of 4°. FSW were carried out under various welding parameters, travel speed of 40, 50, 75 mm/min, rotation speed range (275-1250) rpm and tilt angle of (Ɵ = 3°) with counterclockwise revolution. Many non- destructive inspections and mechanical tests were performed to evaluate welded joints to determine the best welding parameters. Fatigue test has been done at constant stress amplitude cantilever with stress ratio of (R= -1). The results showed that maximum tensile strength and joint efficiency were 360MPa and 86% respectively for dissimilar joints which were welded at 40mm/min travel speed and 550 rpm rotation speed by using threaded cone with double bevels. Keywords: Friction Stir Welding, Dissimilar Al-Alloys, Mechanical Properties, Fatigue Test . ‫دراﺳﺔ ﺳﻠﻮك اﻟﻜﻼل ﻟﻮﺻﻼت ﻏﯿﺮ ﻣﺘﺸﺎﺑﮭﺔ ﻣﻠﺤﻮﻣﺔ ﺑﻄﺮﯾﻘﺔ اﻟﺨﻠﻂ اﻷﺣﺘﻜﺎﻛﻲ ﻣﻦ‬ (2024 -T3 and 7020 -T6) ‫ﺳﺒﺎﺋﻚ اﻷﻟﻤﻨﯿﻮم‬ ‫اﻟﺧﻼﺻﺔ‬ ‫ﯾﮭ دف اﻟﺑﺣ ث اﻟ ﻰ دراﺳ ﺔ ﺳ ﻠوك اﻟﻛ ﻼل ﻟوﺻ ﻼت ﻏﯾ ر ﻣﺗﺷ ﺎﺑﮭﺔ ﻣﻠﺣوﻣ ﺔ ﺑطرﯾﻘ ﺔ اﻟﺧﻠ ط‬ ‫وأﺟرﯾ ت ﻋﻣﻠﯾ ﺔ اﻟﻠﺣ ﺎم ﺑ ﺎﻟﺧﻠط‬. (2024 -T3 and 7020-T6) ‫اﻷﺣﺗﻛ ﺎﻛﻲ ﻣ ن ﺳ ﺑﺎﺋك اﻷﻟﻣﻧﯾ وم‬ ‫ ﻣﻠم ﻋﻠﻰ ﻣﺎﻛﻧﺔ اﻟﺗﻔرﯾز اﻟﻣﺑرﻣﺟﺔ ﺑﺎﺳﺗﻌﻣﺎل اداة ﻟﺣﺎم ﻣن ﻓوﻻذ اﻟﻌ دة‬6.6 ‫اﻷﺣﺗﻛﺎﻛﻲ ﻟﺻﻔﺋﺢ ﺑﺳﻣك‬ ‫ وﻗ د‬.‫ ﻣﻠ م ﻣ ﻊ ﺗﻐﯾﯾ ر ﺗﺻ ﻣﯾم اﻷداة‬6 ‫ ﻣﻠ م وﻣﺳ ﻣﺎر ﻗط ره‬18 ‫ ( وذوﻛﺗ ف ﻗط ره‬R18 ) ‫ﻧ وع‬ ‫ اﺳ طواﻧﻲ ﻣﺳ ﻧن ﻣ ﻊ‬,‫اﺳﺗﻌﻣﻠت ﺛﻼث ﺗﺻﺎﻣﯾم ﻣﺧﺗﻠﻔﺔ ﻟﻸداة ھﻲ ﻣﺧروط ﻣﺳﻧن ﻣﺷ طوف اﻟﺟ ﺎﻧﺑﯾن‬ ‫ أﺟرﯾ ت‬. 0 4 ‫ و ﻣﺧروط ﻣﺷ طوف ﻣ ﻊ ﻛﺗ ف ﻣﻘﻌ ر ﻟﻠ داﺧل ﺑزاوﯾ ﺔ‬04 ‫ﻛﺗف ﻣﻘﻌر ﻟﻠداﺧل ﺑزاوﯾﺔ‬ 439 Eng. & Tech. Journal , Vol.32,Part (A), No.2, 2014 Study Fatigue Behavior of Friction Stir Welded Joints for Dissimilar Aluminum Alloys (2024 -T3 and 7020 -T6) ‫دﻗﯾﻘ ﺔ وﺳ رع‬/‫ ﻣﻠ م‬75‫ و‬50 ‫ و‬40 ‫ ﺳ رع ﻟﺣ ﺎم‬، ‫ﻋﻣﻠﯾﺔ اﻟﻠﺣﺎم اﻻﺣﺗﻛﺎﻛﻲ ﻋﻧد ظروف ﻟﺣ ﺎم ﻣﺧﺗﻠﻔ ﺔ‬ . ‫دﻗﯾﻘﺔ‬/‫ ( دورة‬1250-275 ) ‫دوران‬ ‫أﺟرﯾ ت ﻋ دة ﻓﺣوﺻ ﺎت ﻻ أﺗﻸﻓﯾ ﺔ واﺧﺗﺑ ﺎرات ﻣﯾﻛﺎﻧﯾﻛﯾ ﺔ ﻟﻐ رض ﺗﻘﯾ ﯾم وﺻ ﻼت اﻟﻠﺣ ﺎم وﺗﺣدﯾ د‬ ‫ أﻣﺎ اﺧﺗﺑﺎر اﻟﻛﻼل ﻓﻘد ﻛﺎن ﻣ ن ﻧ وع )اﻧﺣﻧ ﺎء دوار( وﻋﻧ د ﺳ ﻌﺔ اﺟﮭ ﺎد ﺛﺎﺑ ت‬.‫اﻓﺿل ظروف ﻟﻠﺣﺎم‬ 1- =(R) ‫وﻧﺳﺑﺔ اﺟﮭﺎد‬ ‫ ﻣﯾﻛﺎﺑﺎﺳ ﻛﺎل‬360 ‫اظﮭرت اﻟﻧﺗﺎﺋﺞ ان أﻋظم ﻣﻘﺎوﻣﺔ ﺷد ﻟﻠوﺻﻠﺔ اﻟﻣﻠﺣوﻣﺔ وأﻋﻠﻰ ﻛﻔﺎءة ﻟﻠوﺻﻠﺔ ھﻲ‬ ‫ دﻗﯾﻘ ﺔ‬/‫ ﻣﻠ م‬40 ‫ ﻋﻠ ﻰ اﻟﺗﻌﺎﻗ ب ﻟﻠوﺻ ﻼت ﻏﯾ ر اﻟﻣﺗﺷ ﺎﺑﮭﺔ اﻟﻣﻠﺣوﻣ ﺔ ﻋﻧ د ﺳ رﻋﺔ ﺗﻐذﯾ ﺔ‬% 86 ‫و‬ .‫ دﻗﯾﻘﺔ ﺑﺎﺳﺗﻌﻣﺎل ﻋ ُ دة ﻣﺧروطﯾﺔ ﻣﺳﻧﻧﺔ ﻣﺷطوﻓﺔ اﻟﺟﺎﻧﺑﯾن‬/‫ دورة‬550 ‫وﺳرﻋﺔ دوران‬ INTRODUCTION riction stir welding (FSW) is a new solid state welding processes was invented in 1991 in The Welding Institute (TWI). The advantages of FSW technique are that it is environment friendly, energy efficient, there is no necessity for gas shielding for welding Al, mechanical properties as proven by fatigue, tensile tests are excellent, there is no fume, no porosity, no spatter and low shrinkage of the metal due to welding in the solid state of the metal and an excellent way of joining dissimilar and previously non weldable metals [1]. Shusheng Di et al. , 2006 [2] made a comparative study on fatigue properties between 4 mm thick plate of Al 2024-T4 friction stir welds and base material, also studied the influence of zigzag-curve defects across weld section on the fatigue properties of FSW joints. The welding parameters used were rotational speed of 800–1000 rpm, travel speed of 150–250 mm/min and the tilt angle of 3◦. The fatigue tests were carried out in a high-frequency fatigue test machine with stress ratio R = 0.1. They conclude that the fatigue crack always appeared at the weld root site also root flaws produced by ‘zigzag-line’ defects up to 0.35 mm deep hardly influenced the mechanical properties. V. Sinka 2010 [3] studied Friction stir lap welding of two high strength heat treatable aluminum alloys (2024 with 7075). EDS microanalyses were carried out in the nugget by means of a scanning electron microscope in order to map the extension of the mixing of the two alloys. The mechanical properties were evaluated by means of microhardness measurements in the mixed region of the FSW joint. Joint microstructure showed a characteristic mixture pattern of the two alloys. It exhibited a regular pattern of elongated stripes on the advancing side and a turbulent pattern on the retreating side of the joint, while maintaining the difference in their hardness values. Also no detectable interdiffusion of the alloying elements was found. D.Muruganandam et al., 2010 [4] investigated the mechanical and microstructural properties of dissimilar 2024-T3 and 7075-T6 aluminium plates with 5 mm thickness had been joined by friction stir welding (FSW). Optimized welding parameters were set to welding speed of 160 mm/min and clockwise rotating axle with tilt angle of 3o. High cycle fatigue tests (axial stress amplitude) had been performed using a constant stress ratio of (R=0.1). They concluded that the maximum microhardness value reaches to 150 HV in the weld center and decreases in the HAZ and the welding efficiency reached to about 87% and the fatigue strength was 44 MPa at about 2*106 cycles. A.A.M. da Silva et al., 2011 [5] investigated mechanical properties and microstructural features as well as material flow characteristics in dissimilar F 440 Eng. & Tech. Journal , Vol.32,Part (A), No.2, 2014 Study Fatigue Behavior of Friction Stir Welded Joints for Dissimilar Aluminum Alloys (2024 -T3 and 7020 -T6) friction stir welded joints of 10 mm thick (2024-T3 and 7075-T6 sheets). Welds have been performed at fixed feed rate (254 mm/min) with varying the rotation speed in three levels (400, 1000 and 2000 rpm). The conclusions can be drawn as follows :(1) The minimum hardness value of naturally aged samples has been found in the HAZ at the retreating side (about 88% of 2024-T3 base material). (2) The weld efficiency in terms of tensile strength for the 1000 rpm FSW condition is approximately 96%. Fracture of the specimens has occurred in the HAZ at the retreating side (2024-T3). Pouya et al.,[6] investigated the effect of friction stir welding (FSW) parameters on the weldability and the characteristics of dissimilar welds Al-alloys (2024-T3 and 7075-O). A number of FSW experiments are carried out to obtain high-quality welds by adjusting the rotational and welding speeds. The weldability and blending of two materials are evaluated by using the macrostructural analysis; also the mechanical properties of the welds are studied through microhardness distribution and tensile tests. It was clarified that increasing the rotational speed and reducing the welding speed resulted in a decrease in the overall hardness value in the stir zone. The aims of the present work are; first, is to find the best conditions of friction stir welding parameters to join the dissimilar Al-alloys (2024-T3 and 7020-T6) after welding at different welding speeds, rotation tool speeds and tool designs. Second, investigation of the fatigue behavior of dissimilar welded joints for above mentioned alloys. EXPERIMENTAL WORK Materials Aluminum alloys of two types’ 2024-T3 and 7020-T6 (T3: Solution heat treated and cold worked, T6: Solution heat treated and artificially aged) with 6.6mm thickness were used in this study. Plates were cut into the required size of 150 ×50 mm by punch cutter and then machined to the required size using CNC milling machine. Butt joint configuration was prepared to fabricate friction stir welding (FSW) joints. XRF analysis had been done for those Al- alloys which inspected by spectroscopy Oxford X-Met 3000TX and the results of chemical compositions are represented in the Table (1). Welding Tools The welding tool used in this study was made of R18 tool steel (depending on DIN standards) with 18mm shoulder diameter, 6mm pin diameter and 6.3 mm pin length (95% of plate thickness). Figure (1) indicates the tool designs used for FSW process. Experimental FSW Procedure NC milling machine had been used to join dissimilar alloys (2024 T3-7020 T6) with 6.6 mm thick plate with reversed revolution (tool rotation: counter clockwise) by placing 7020-T6 alloy (the softer material) on advancing side and 2024-T3(the harder material) on retreating side with tilt angle(Ɵ) of 3o. Inspections and Tests Nondestructive Testing Portable ultrasonic flaw detector has been used for detecting internal defects in the weld using angle probe of 70o and 2 MHz frequency. Also ERESCO MF4 441 Eng. & Tech. Journal , Vol.32,Part (A), No.2, 2014 Study Fatigue Behavior of Friction Stir Welded Joints for Dissimilar Aluminum Alloys (2024 -T3 and 7020 -T6) X-ray radiography technique has been used to examine the internal defects in weldments. The optimum macrograph conditions for this inspection were: Voltage: 60 volt, Amperage: 5.5 mA, exposure time: 200 sec. and (Source to film distance): 600 mm. X-ray diffraction (XRD) analysis XRD analysis was carried out on five samples which cut from transverse dissimilar welded joints. The dimensions of samples were (L: 10×W: 10× T: 6) mm which includes four zones; [Stir zone (SZ), Thermo-mechanical (TMAZ), Heat affected zone (HAZ) and base metal (BM)] as shown in Figure (2). XRD instrument type Scintag inc X2 X-ray was used with parameters as follows: Voltage: 42 KV, Current: 37 mA with Cu-radiation as x-ray source. Microstructure Examination Samples were taken from the cross section of FSW welds, and then grinding process was carried out using Al2O3 emery papers in sequence, 320, 500, 1000 and 1200 with using water for cooling the samples in each step. After that polishing process was carried out with using diamond paste to get polished mirror surfaces. Etching process was done to these samples using Keller’s etchant which consists of (95ml H2O+2.5 ml HNO3+1.5 ml HCl+ 1 ml HF) to develop the microstructure of welded joints and base alloys. Microstructure examination of these samples had been investigated using MEIJI MT9430 high resolution optical microscope. Mechanical tests Tensile Test Tensile specimens had been cut perpendicular to the weld line of FSW plates using CNC milling machine to the sub-size specimen geometry according to (ASTM E8M-04). Tensile strength had been conducted from stress-strain curves of the base alloys and welded joints. Microhardness Test Microhardness test was carried out using Vickers hardness tester type (HVS1000). The measurements were done on transverse section to weld line for all welds after surface preparation from grinding and polishing processes until reaching to mirror polished surface .This test was done by measuring the microhardness values at spacing 1mm apart from one point to another with applied load of 9.8 N for 15 seconds. Fatigue Test Fatigue test was done at constant stress amplitude cantilever with fully reversed (R= -1), and the specimen dimensions according to the apparatus standard was L (length) ×W (width) ×T (thickness) =100×10×6.6 mm respectively. Ten samples were taken from each welded plate to implement the tests. RESULTS AND DISCUSSION Radiography Inspection Results Radiography test inspection has been done as shown in Figure (3) which represents the x-ray photograph for accepted dissimilar FS welds, which mean with small or no defects. It was seen from welded sample (A1) that there is a crack in the end which is not defect but it's due to tool outlet that will cut away 442 Eng. & Tech. Journal , Vol.32,Part (A), No.2, 2014 Study Fatigue Behavior of Friction Stir Welded Joints for Dissimilar Aluminum Alloys (2024 -T3 and 7020 -T6) with the tool entrance. For welded sample (3A) there is a surface defect due to low or incomplete heat flow. This defect was removed by machining processes. For welded sample (B2) there is a small line defect which called (Joint line remnant) or what called (kissing bond). This is due to inadequate removal of oxide from plate edges also the increase in tool shoulder diameter may lead to this type of defect. This defect is not considerable and has a little effect on the mechanical properties. This defect appears in retreating side near the weld line [7,8] .The welded sample (B3) is free from defects when examined by this technique. Macro and Microstructure Results Stereoscopy microscope was used to examine the cross section of some FS welding joints. Figure (4) shows the uniform flow in sample (B3) between two alloys [2024-T3 (black region) with 7020-T6 (white region)] at a tool revolution of 920 rpm and feed of 40 mm/min. Also the FSW zones, advancing and retreating sides are clear in this image. Microstructure examination had been done for the three modes as follow: Mode 1 The used tool was R18 tool steel which includes threaded cone pin with double bevel. FSW process was conducted with rotation speed of 275rpm and travel feed of 40mm/min. The nugget zone in this case contains an ultrafine grain with second phase precipitates as shown in Figure (5a and b). Also the same microstructure has been observed using higher rotation speed of 550 rpm but with better properties. With increasing the feed rate (as in sample A3) a reduction in mechanical properties will happen, also same flow lines has been noticed as in Figure (5c). Mode 2 The R18 tool steel with threaded cylinder pin and concave shoulder of 4o was used to increase the flow of alloys. Using revolution of 800 rpm and feed of 40 mm/min as in sample (B1) didn’t give good properties in spite of evolution of onion rings and flow lines as in Figure (6a and b) because of inappropriate conditions; also the heat affected zone (HAZ) has similar grain size and distribution to the base metal (alloy) as in Figure (6c). While using a revolution of 920 rpm for this tool as in sample (B2) lead to a defect named “kissing bond” which is an entrance of oxygen to form high density Al2O3 with an amorphous structure [9], as shown in Figure (6d). It was found that increasing of tool revolution to 1100 rpm enhances the mechanical properties as shown in sample (B3) which gives the best properties in this case. While the rotation speed of 1250 rpm reduces the mechanical properties as in sample (B4). The three weld zones were illustrated in the photographs Figure (6e, f and g). Mode 3 The R18 tool steel with beveled cone and concave shoulder of 4° is used. A revolution of 1250 rpm and feed of 40 mm/min give the best properties for this case. The microstructure is similar to the previous cases due to convergence of welding conditions. Tensile Test Results The tensile strength (σt) of two base alloys was 499 MPa and 418 MPa for Al 2024-T3 for Al 7020-T6 respectively. 443 Eng. & Tech. Journal , Vol.32,Part (A), No.2, 2014 Study Fatigue Behavior of Friction Stir Welded Joints for Dissimilar Aluminum Alloys (2024 -T3 and 7020 -T6) Table (2) Indicates the FSW welding conditions and tensile test results for dissimilar welded joints. Different feed rate have been used with mode 1 tool design; it has been found that 40 mm/min travel speed gives the best result, so it has been generalize for other tool designs modes. Microhardness Results A summary of results for three cases are illustrated in Figure (7). From these results minimum microhardness has been got in nugget zone due to high heat input, while in some cases a little rise or drop in HAZ zone has been got due to different heat flow and distribution of 2nd phase precipitates. This is clear from xray diffraction results as in Figure (8) which represents the nugget zone phase analysis. This variation result from different tool designs and welding conditions. Microhardness values were lower in the retreating side than that in the advancing side because the material dragged by the shoulder during the welding from the retreating side of the weld, around the rear of the tool, and deposited on the advancing side. [10] Fatigue Test Results Fatigue test results of base alloys 2024-T3 and 7020-T6 were 160MPa and 150 MPa respectively as shown in Figure 9. While Figure (10) shows the S-N curve of dissimilar joints welded at the best welding parameters of travel speed of 40mm/min and rotation speed of 550 rpm with using tool Mode 1, and the fatigue endurance was 130 MPa. Figure (11) shows S-N curve of dissimilar joints welded at the best welding parameters of travel speed of 40mm/min and rotation speed of 1100 rpm with using tool Mode 2 , and the fatigue endurance was 124 MPa. While Figure (12) shows S-N curve of dissimilar joints welded at travel speed of 40mm/min and rotation speed of 1250 rpm with using tool Mode 3 and the fatigue endurance was 115 MPa. It has been found that increasing feed and travel speed had a deterioration effect on fatigue properties due to the reduction in required input heat to get sound weld. Also the best fatigue properties has been shown for FS welded specimen (A1) with maximum joint efficiency (86%) which is defined as the ratio (tensile strength of weld / tensile strength of base metal), This result is in agreement with other workers [11]. Analysis Fatigue Images by Scanning Electron Microscope In order to study the fatigue behavior of dissimilar FSW joint, a scanning electron microscope images were taken for different regions in fracture section surfaces. Figure (13a) shows the facets that formed in fracture section of FSW joint (sample A1) which is one of the aspects of cleavage fracture; also micrograph Figure (13 b) shows the macro cracks that generated from the surface in the fracture zone. A fatigue zone has been noticed in fracture section of FSW joint (sample B3), which is the upper part in macrograph while the lower part is the final fracture region and some grooves has been noticed as shown in Figure (13c). Different topography and fractography related to the difference in FSW parameters are also investigated. 444 Eng. & Tech. Journal , Vol.32,Part (A), No.2, 2014 Study Fatigue Behavior of Friction Stir Welded Joints for Dissimilar Aluminum Alloys (2024 -T3 and 7020 -T6) CONCLUSIONS 1. The tensile test results showed that the fracture was in the weld zone or in the weld / HAZ borderline. 2. Mechanical and fatigue properties of the FS welds are reduced with increasing welding speed for dissimilar Al-alloys (2024-T3 and 7020T6), and the lower speed gives better mechanical properties. 3. Making flutes in the tool design increases the flow of metals thus increases the mechanical properties, while making concave shoulder has less effect. 4. The best mechanical properties and fatigue endurance have been obtained at FS welding parameters, tool revolution speed of 550 rpm and feed rate of 40 mm/min with using threaded cone with double bevels. REFERENCES [1].Rajiv S. Mishra, Murray W. Mahoney,” Friction Stir Welding and Processing” editors, pp. 1-5.DOI:10.1361/fswp, 2007. [2].Shusheng Di, Xinqi Yang, Guohong Luan, Bo Jian “Comparative Study on Fatigue Properties between AA2024-T4 Friction Stir Welds and Base Materials”. Materials Science and Engineering, Vol. A 435–436, pp. 389–395, 2006. [3].V. Sinka,” FSW Joint Microstructure of Two High Strength Aluminum Alloys: A 2024 / A 7050”, Acta Metallurgica Slovaca, Vol. 16, No.2, pp. 116121, 2010. [4].Muruganandam, D., Ravikumar, S. and Das S.L., "Mechanical and Microstructural Behavior of 2024–7075 Aluminum Alloy Plates Joined by Friction Stir Welding" ,Frontiers in Automobile and Mechanical Engineering (FAME) , 2010 , Conference, pp.247,251, No.25-27 . 2010. [5].A.A.M da Silva,E.Arruti, G.Janeiro,E .Aldanondo, P.Alvarez, and A.Echeverria,” Material Flow and Mechanical Behavior of Dissimilar AA2024T3 and AA7075-T6 Aluminum Alloys Friction Stir Welds”, Materials and Design, Vol. 32, pp.2021–2027. , 2011. [6].Pouya Bahemmat ,Mohammad Haghpanahi,Mohammad Kazem Besharati Givi and Kambiz Reshad Seighalani,” Study on Dissimilar Friction Stir butt Welding of AA7075-O and AA2024-T4 Considering the Manufacturing Limitation”, Int. J. Adv. Manuf. Technol. Vol.59,pp.939 –953, 2012. [7].A J Leonard and S A Lockyer,” Flaws in Friction Stir Welds ”, 4th International Symposium on Friction Stir Welding, Park City, Utah, USA, TWI Ltd, Granta Park, Great Abington, Cambridge, CB1 6AL, UK14-16 May, 2003. [8].Hakan AYDIN , Ali BAYRAM , M. Tahir YILDIRIM and Kurtuluş YIĞIT,” Influence of Welding Parameters on the Fatigue Behaviours of Friction Stir Welds of 3003-O Aluminum Alloys”, ISSN 1392–1320 MATERIALS SCIENCE (MEDŽIAGOTYRA). Vol. 16, No. 4. 2010. [9].CAIZHI ZHOU, XINQI YANG and GUOHONG LUAN,” Effect of Kissing Bond on Fatigue Behavior of Friction Stir Welds on Al 5083 Alloy”, J. Mater. Sci., Vol. 41, pp.2771–2777, 2006. 445 Eng. & Tech. Journal , Vol.32,Part (A), No.2, 2014 Study Fatigue Behavior of Friction Stir Welded Joints for Dissimilar Aluminum Alloys (2024 -T3 and 7020 -T6) [10]. Aissani, Mouloud, Saliha Gachi, Fouad Boubenider, and Younes Benkedda. "Design and optimization of friction stir welding tool." Materials and Manufacturing Processes 25, no. 11 pp.1199-1205, (2010). [11].P. Cavaliere and F. Panella,” Effect of Tool Position on The Fatigue Properties of Dissimilar 2024-7075 Sheets Joined by Friction Sir Welding”, Journal of Materials Processing Technology, Vol. 2 0 6 , pp.249–255, 2008. Table (1) The chemical compositions of Al- alloys. Al-2024-T3 Al-7020-T6 Al-2024-T3 Al-7020-T6 Standard value Measured value Alloy wt% Si Fe Cu Mn Mg Zn Ni Ti Pb Sn Others Al 0.57 0.37 4.9 0.7 1.01 0.18 0.13 0.17 ≤0.05 0.196 ≤ 0.05 Cr Rem. 0.67 0.15 0.55 0.08 0.60 4.8 ≤0.05 0.22 ≤0.05 0.16 ……. Rem. ≤0.5 ≤0.5 3.84.9 0.30.9 -1.2 1.8 ≤0.25 ≤0.05 ≤0.15 ≤0.05 ≤0.05 ≤ 0.05 Cr Rem. ≤0.35 ≤ 0.4 ≤ 0.2 0.050.5 11.4 4.5 ≤0.05 ≤0.05 ...... ...... 0.22Cr+ 0.14Zr Rem. 446 Eng. & Tech. Journal , Vol.32,Part (A), No.2, 2014 Study Fatigue Behavior of Friction Stir Welded Joints for Dissimilar Aluminum Alloys (2024 -T3 and 7020 -T6) Table (2) Results of tensile tests for dissimilar welded joints. Tool Design Mode 1 Tool Rev Joint Efficiency % 360 86.1 % 144 34.5 % 184 44 % 160 38.3% 260 62.2% 345 82.6% 275 65.8% 185 44 (rpm) A1 275 40 A2 550 50 A3 550 75 B1 800 40 B2 920 40 B3 1100 40 B4 1250 40 C1 630 40 C2 920 40 20247020 205 49 C3 1250 40 20247020 290 69.4% Mode 2 Mode 3 σt ,MPa (weld) Travel Speed (mm/min) No. a b Al- alloys 20247020 20247020 20247020 20247020 20247020 20247020 20247020 20247020 c Figure (1) Tool designs used in FSW a) Mode 1, b) Mode 2, c) Mode 3. 447 Eng. & Tech. Journal , Vol.32,Part (A), No.2, 2014 7020 (Advancing side) 1(Base Metal) Study Fatigue Behavior of Friction Stir Welded Joints for Dissimilar Aluminum Alloys (2024 -T3 and 7020 -T6) weld center 2024 (Retreating side) 2(HAZ+TMAZ) NZ(weld) 3(HAZ+TMAZ) 4 (Base Metal) Figure (2) XRD specimen parts or divisions for FSW joint of dissimilar Al-alloys. Surface defects Small line defect A1 B2 B3 Figure (3) Photographs of X-ray radiography for FSW joints of samples A1, B2, B3 448 Eng. & Tech. Journal , Vol.32,Part (A), No.2, 2014 Study Fatigue Behavior of Friction Stir Welded Joints for Dissimilar Aluminum Alloys (2024 -T3 and 7020 -T6) Advancing Ret reat ing side side TM AZ Nugget zone HAZ Figure (4) Macrograph of cross section of welded sample (B3). a b 2 nd phase c 2 α-Al precipitates nd phase α-Al precipitates Figure (5) Microstructures of nugget zones in dissimilar welds with double bevels threaded cone tool, 400X. 449 Eng. & Tech. Journal , Vol.32,Part (A), No.2, 2014 Study Fatigue Behavior of Friction Stir Welded Joints for Dissimilar Aluminum Alloys (2024 -T3 and 7020 -T6) Onion ring a b c Kissing bond d f e d Precipitates f g Figure (6) Microstructures of FSW welds for samples B1, B2 and B3. a) Flow lines of sample B1 400X,b) onion rings,400X ,c) Base metal in sample B1 1400X d) Kissing bond in sample B2 200X, e) HAZ of sample B3 1400X , f) TMAZ of sample B3 1400X, g)nugget zone of sample B3 Figure (7) Microhardness distrbutions for three cases of dissimliar welds. 450 Eng. & Tech. Journal , Vol.32,Part (A), No.2, 2014 Study Fatigue Behavior of Friction Stir Welded Joints for Dissimilar Aluminum Alloys (2024 -T3 and 7020 -T6) Al M g32(AlZn) 49, Al 3M g2, CuZn 2 M g32(AlZn) 49, AlCuM g, AlCu Al Al2CuM g, M g32(AlZn) 49, AlCuM g, Al 3M g2, AlM g AlCu Al2CuM g, Al 3M g2, CuZn 2 Al Al Figure (8) XRD analysi result for nugget zone of dissimilar weld (A1 sample). Figure (9) S-N curves of base alloy 2024-T3 and 7020-T6. A1 Figure (10) S-N curve of dissimilar joint welded with tool Mode 1. 451 Eng. & Tech. Journal , Vol.32,Part (A), No.2, 2014 Study Fatigue Behavior of Friction Stir Welded Joints for Dissimilar Aluminum Alloys (2024 -T3 and 7020 -T6) B2& B3 Figure (11) S-N curves of dissimilar joints welded with tool Mode 2. C3 Figure (12) a S-N curve of dissimilar joint welded with tool Mode 3. b Facets c Macro Fatigue zone Final fracture Figure (13 a) Striation in fracture section of dissimilar weld (sample A1), b) Primary cracks in the same sample (A1) c) Fatigue zone in fracture section of sample (B3). 452