IJSTE - International Journal of Science Technology & Engineering | Volume 4 | Issue 5 | November 2017 ISSN (online): 2349-784X
Influence of Friction Stir Welding Parameters on Microstructural and Mechanical Properties of Dissimilar AA6061 and AA7075 Alloy Joints M. Melwin Jagadeesh Sridhar Assistant Professor Department of Mechanical Engineering Kings College of Engineering, Punalkulam
B. Adhichelvan Assistant Professor Department of Mechanical Engineering Kings College of Engineering, Punalkulam
Abstract The main objective of this research is to conduct an investigation into the effect of welding parameters on the microstructural and mechanical properties of friction stir (FS) welded butt joints of dissimilar aluminum alloy AA6061 and AA7075. Friction stir welding (FSW) is a relatively new solid-state joining process. This joining technique is energy efficient, environment friendly, and versatile. This will be used to join aerospace aluminum alloys and other metallic alloys that are hard to weld by conventional fusion welding. In this process, two metal pieces, AA6061 and AA7075, 100 x 50 x 6mm thick, are welded under different welding parameters like tool rotation speed and transverse feed. The effects of welding parameters were evaluated by studying the resulting mechanical properties such as hardness distribution and tensile properties for axial welded zone. Keywords: Aluminum Alloy AA6061, AA7075, Friction Stir Welding, conventional fusion welding, Hardness and microstructure ________________________________________________________________________________________________________ I.
INTRODUCTION
Aluminum alloys are predominant for the fabrication of structures and components which require low weight, high strength or electric current carrying capabilities to meet their service requirements. Among all aluminum alloys, AA 6061 alloy plays major role in the aerospace industry in which magnesium and silicon are the principal alloying elements. It is extensively used in the aerospace applications because it has good formability, weldability, machinabilty, corrosion resistance and good strength compared to other aluminum alloys. When using the conventional arc welding techniques, long butt or lap joints between AA 6061 and other aluminum alloys are particularly difficult to make without distortion because of high thermal conductivity and special welding procedures and high levels of welder skill are generally required. AA 7075 aluminum alloy is an aluminum alloy, with zinc as the primary alloying element. It is strong, with strength comparable to many steels, and has good fatigue strength and average the first AA 7075 was developed in secret by a Japanese company, Sumitomo Metal, in 1943.AA 7075 was after a period of time used for airframe production in the Imperial Japanese Navy. Friction Stir Welding (FSW) is a solid state welding process developed and patented by The Welding Institute (TWI) in 1991. It is emerged as a novel welding technique to be used in high strength alloys that were difficult to join with conventional welding techniques Friction Stir Welding (FSW) is a relatively new joining process that has exhibited many advantages over traditional arc welding processes, including greatly reducing distortion and eliminating solidification. The present work aims to determine the feasibility to weld two pieces of aluminum plate (100 x 50 x 6 mm) by friction stir welding process and study the effect on the mechanical properties of welding joints. In recent years, demands for light-weight and/or high strength sheet metals such as aluminum alloys have steadily increased in aerospace, aircraft, and automotive applications because of their excellent strength to weight ratio, good ductility, corrosion resistance and cracking resistance in adverse environments. Semi-solid metals (SSM), mostly aluminum alloys, have emerged in the usage of casting components in various applications. Joining between SSM356-T6 casting aluminum alloy and AA6061-T651 is a common combination that requires good strength joints and an easy process. Joining of aluminum alloys has been carried out with a variety of fusion and solid state welding processes. As the FSW process does not release toxic acids or fumes, it is an environment protective process. No consumable filler material or edge preparation is normally necessary. The distortion is significantly less than that caused by arc fusion welding techniques. By welding Aluminum alloys by fusion welding process there is possibility of cracks, porosity, alloy segregation and hot cracking and the fusion welding process completely alters microstructure and varies the mechanical properties [3]. By FSW both similar and dissimilar materials can be successfully joined.
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Influence of Friction Stir Welding Parameters on Microstructural and Mechanical Properties of Dissimilar AA6061 and AA7075 Alloy Joints (IJSTE/ Volume 4 / Issue 5 / 023)
Table – 1 (Chemical composition of A6061) Component Amount (wt.%) Aluminum 95.8 - 98.6 Magnesium 0.8-1.2 Silicon 0.4 – 0.8 Iron Max. 0.7 Copper 0.15-0.40 Zinc Max. 0.25 Titanium Max. 0.15 Manganese Max. 0.15 Chromium 0.04-0.35 Others 0.05 Table – 2 (Chemical composition of A7075) Component Amount (wt. %) Aluminum 87.1 - 91.4 Chromium 0.18 - 0.28 Copper 1.2 – 2 Iron 0.5 max Magnesium 2.1 - 2.9 Manganese 0.3 max Silicon 0.4 max Titanium 0.2 max Zinc 5.1 6.1 Others 0.05 max
II. EXPERIMENTAL PROCEDURE FRICTION STIR WELDING The Friction stir welds between AA7075-T651 and AA6061-T651 aluminum alloys were produced using FSW machine with hydraulic power pack motor of 2.2Kw /440V with 3000 rpm maximum rotational speed; 5000 mm/min as X axis rapid traverse speed and maximum axial thrust as 50kN. The thicknesses of both plates were 6 mm. The plates were in a butt joint configuration and the welding process was carried out normal to the rolling direction of the plate. The dimensions of the aluminum alloy plates are 100 mm length and 50 mm width. The welding process was accomplished at three rotational speeds, 710, 1000 and 1400 rpm, the axial feed is, 14, 20 and 28 mm/sec keeping axial load 12 kN and tilt angle 0º as constant. Simple Square (SS) tools used were machined from high speed tool steel and were hardened to 55HRC
Fig. 1: Schematic drawing of friction stir welding (FSW)
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Influence of Friction Stir Welding Parameters on Microstructural and Mechanical Properties of Dissimilar AA6061 and AA7075 Alloy Joints (IJSTE/ Volume 4 / Issue 5 / 023)
Fig. 2: (work piece)
III. METHODOLOGY Taguchi Design of Experiments Taguchi method is a powerful tool in quality Optimization makes use of a special design of orthogonal array (OA) to examine. Number of experiments used to design the orthogonal array for 2 parameters and 3 levels of welding parameters Minimum experiments = [(L-1)X p]+1 = [(3-1)X 2]+1 = 5 ≈ L9 Table – 3 (Friction stir welding parameters) Work piece Spindle speed(rpm) Feed (mm/sec) 1 710 14 2 710 20 3 710 28 4 1000 14 5 1000 20 6 1000 28 7 1400 14 8 1400 20 9 1400 28
Table 3 represents the input parameters of the friction stir welding on dissimilar AA6061 and AA7075 alloy. Rockwell Hardness Test For soft materials such as copper alloys, soft steel, and aluminum alloys a 1/16" diameter steel ball is used with a 100-kilogram load and the hardness is read on the "B" scale. In testing harder materials, hard cast iron and many steel alloys, a 120 degrees diamond cone is used with up to a 150 kilogram load and the hardness is read on the "C" scale. There are several Rockwell scales other than the "B" & "C" scales, (which are called the common scales). A properly reported Rockwell value will have the hardness number followed by "HR" (Hardness Rockwell) and the scale letter. For example, 50 HRB indicates that the material has a hardness reading of 50 on the B scale.
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Influence of Friction Stir Welding Parameters on Microstructural and Mechanical Properties of Dissimilar AA6061 and AA7075 Alloy Joints (IJSTE/ Volume 4 / Issue 5 / 023)
Fig. 3: Rockwell hardness testing machine Table – 4 (Rockwell hardness test) (Larger is better) Rockwell hardness Spindle speed Axial feed (rpm) (mm/sec) T1 T2 T3 Avg (hrc) 710 14 30 21 36 29.00 710 20 20 38 27 28.33 710 28 24 22 27 24.33 1000 14 28 22 26 25.33 1000 20 27 23 22 24.00 1000 28 23 26 21 23.33 1400 14 21 32 25 26.00 1400 20 21 28 26 25.00 1400 28 28 22 24 24.66
Table 4 shows maximum hardness (HRC) obtained from lowest spindle speed (mm/sec) and lowest axial feed (mm/sec). Table – 5 (Response Table for Signal to Noise Ratios Larger is better) Spindle speed Axial Level (rpm) Feed(mm/sec) 1 28.67 28.54 2 27.68 28.20 3 28.03 27.64 Delta 0.99 0.90 Rank 1 2
The table 5 represent the spindle speed is an influencing parameter (Rank 1) for producing the higher hardness on dissimilar AA 6061 and AA 7075 alloy and optimized by signal to noise ratio. The F-test The F-test is used for comparisons of the components of the total deviation. For example, in one-way or single-factor ANOVA, statistical significance is tested for by comparing the F test statistic F= variance between treatment / Variance within treatment Table – 6 (ANOVA values of friction stir welding process parameters) Source DF Seq SS Adj SS Adj MS F P Spindle speed 2 14.000 14.00 7.00 5.74 0.067 Feed 2 10.918 10.91 5.45 4.48 0.095 Error 4 4.878 4.878 1.21 --Total 8 29.796 -----
S = 1.10429 R-Sq = 83.63% R-Sq(adj) = 67.26%
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Influence of Friction Stir Welding Parameters on Microstructural and Mechanical Properties of Dissimilar AA6061 and AA7075 Alloy Joints (IJSTE/ Volume 4 / Issue 5 / 023)
The table 6 shows the analysis of variance values of friction stir welding process and higher value of F-test represents spindle speed is a dominating parameter for achieving higher hardness. Main Effects Plot (data means) for Means SPEED
27.5
FEED
Mean of Means
27.0 26.5 26.0 25.5 25.0 24.5 24.0 710
1000
1400
14
20
28
Fig. 4: (main effects plot for means)
Interaction Plot (data means) for Means 14
20
28 28.8 27.6
SPEED 710 1000 1400
26.4
SPEED
25.2 24.0 FEED 14 20 28
28.8 27.6 26.4
FEED
25.2 24.0 710
1000
1400
Fig. 5: (interaction plot for means)
The figure 5 shows the interaction plot between process parameters of friction stir welding such as spindle speed and axial feed on dissimilar AA6061 and AA 7075 alloy and also indicate work spindle speed has dependable parameter of higher hardness.
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Influence of Friction Stir Welding Parameters on Microstructural and Mechanical Properties of Dissimilar AA6061 and AA7075 Alloy Joints (IJSTE/ Volume 4 / Issue 5 / 023)
Contour Plot of HRC vs FEED, SPEED 27.5
HRC < 24 24 - 25 25 - 26 26 - 27 27 - 28 28 - 29 > 29
25.0
FEED
22.5
20.0
17.5
15.0 800
900
1000 1100 SPEED
1200
1300
1400
Fig. 6: (contour plot of HRC vs Spindle speed, axial feed)
The figure 6 denotes the graphical representation of optimal parameters of higher hardness in friction stir welding process. IV. CONCLUSION In the present experimental work, dissimilar AA6061 and AA7075 alloy joints were made by FSW under different spindle speed and different axial feed. Summarizing the main features of the results, following conclusions can be drawn: Dissimilar AA 6061 and AA 7075 alloy joints producing better weldability and higher hardness, during friction stir welding process. Spindle speed played an important role for achieving higher hardness in friction stir welding process. The optimum parameter of friction stir welding process for producing higher hardness is spindle speed 710 rpm and axial feed 14 mm / sec. REFERENCES [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14]
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