Influence of Conical Taper Tool Profile on Mechanical and Micro Structural Characterization of Friction Stir Welded 5083 Aluminum Alloy

 

P. Kumar*, P. Satish Kumar, M. Shiva Chander

Department of Mechanical Engineering, S R Engineering College, Warangal, Telangana, India.

 

ABSTRACT:

A study was made on welding of 4mm-thick aluminum alloy 5083 plates using friction stir welding. Table of experiments was prepared based on abilities of universal milling machine. The Experiments are conducted at different tool rotations speeds 900r/min, 1120r/min, 1400r/min and 1800r/min, the welding speed is at 40mm/min were taken. Analysis is made with the conical taper profile tool. Samples for microstructure analyses, Rockwell micro-hardness measurements and tensile-testing samples were prepared. It was observed that the better mechanical properties were achieved at moderate tool rotational speed, and equip-axed grains obtained at taper profile tool, grain size were obtained half of the base material.

 

 

1. INTRODUCTION:

The 5083 aluminum alloy is exhibits good corrosion resistance to seawater, better mechanical properties. It has good formability, machinability and weldability. The 5083 aluminum alloy is used for providing of welded components for ship building and railway vehicles. And also it has the high strength of the non-heat treatable alloys of aluminium. [1-2] it is not recommended for use in temperatures in excess of 65⁰Cto corrosive surroundings. [3] Many studies were described on the weldability of 5083aluminium alloy. [4-6]Aluminum alloys are friction-stir process (FSP) then the properties of super plastic are obtained, as a consequence of grain refinement. [7] Friction stir processing (FSP) is used to transform a heterogeneous microstructure to a more homogeneous, before not reaching its melting temperature. Welding is a process for joining different materials. In order to join two or more sample plates of metal through any welding process, the most essential requirement is heat.

 

Fig. 1 working principle of FSW

 

TABLE I. BASE METAL MECHANICAL PROPERTIES OF AA5083 ALLOY

Material	Density (N/mm2)	UTS (N/mm2)	yield strength
AA5083	2.66	240	135

 

2. LITERATURE REVIEW:

M. K. Bilici et al studied that the effects of tool geometry and properties on friction stir spot welding properties of polypropylene sheets.  In his study Four different tool pin geometries, with varying different pin angles, pin lengths, and shoulder diameters and shoulder angles were used for friction stir spot welding. All the welding operations were done at the normal room temperature.  And the Lap-shear tensile tests were carried out to find the weld static strength. Friction stir spot weld formation and weld strength results are studied from the experiments of the effect of tool geometry.  The optimum tool geometry for 4 mm thickness polypropylene sheets ware determined. The tapered cylindrical pin given the biggest and the straight cylindrical pin given the lowest lap-shear fracture load.

 

T. DebRoyet et al (2010) stated that the mechanical properties of friction stir welds while varying process parameters in 5083-H111 aluminum alloy. The used tool had a shoulder diameter of 20 mm, and a pin with a length, diameter of 4.5, 5.0 mm respectively.  And the tool was made from SK tool steel, tilted at 2⁰. Welding was done at 500, 900, 1800 rpm and 40 to 120 mm/min. Tensile tests were performed on all welds. The weld process was performed at 500 rpm and 900 rpm showed a reduction in quality when the traverse feed increased. At 1800 rpm, all weld speeds produced defects. In turn, the welds were exhibited very low quality of mechanical properties. All fractures during tensile test occurred in the stir welding zone. So the optimum FSW parameters for this experiment were 900 rpm and 120 mm/min which had an ultimate tensile strength around 250MPa.

 

P. Satish Kumar observed in his project that, a study was made on effect of tool rotational speed on micro structural and mechanical properties of 5083 Aluminum alloy.  It is observed that higher mechanical properties are obtained at a rotational speed of 710 rpm. And Fine microstructure was also obtained at the above mentioned condition.

 

M. shiva chander et al stated that, welding a 4 mm thick 5083 aluminum plates using friction stir welding. Experiments were prepared based on different rotational speeds and at a welding speed of 40mm/min. Threaded profile tool was used for the analysis. So From this, the mechanical properties are achieved at moderate speed.

 

3. EXPERIMENTAL PROCEDURE:

A.      Material:

The plates of 4 mm thickness AA5083 aluminum alloy were cut into size 150 mm x 60 mm and machined with square butt joint type. The initial configuration was come out by securing the plates in butt position using specially designed and fabricated fixture. Here the non-consumable high speed steels are used for welding. The chemical composition of the AA5083 material used in the present study is given in Table II.

 

TABLE II. CHEMICAL COMPOSITION OF AA5083 IN WT %

Material	Mg	Mn	Si	Cr	Fe	Zn	Ti	Cu	Al
AA5083	4.5	0.7	0.4	0.15	0.4	0.25	0.15	0.1	Rest

 

B.      Friction Stir Welding

The welding was carried out in a universal milling machine by changing the tool speed. The tool that tapered with cylindrical shoulder was used to attach the joints. Based on the literature survey, with the availability of speeds on the machine, three different rotational speeds were selected to carry out the experiment. The welding parameters and tool dimensions are as shown in Table III.

 

TABLE III. FSW PROCESS PARAMETERS

Process Parameter	Values/Types
Material used	AA5083
Type of Joint	Butt joint
Thickness of the material (mm)	4
Tool rotation speed(rpm)	900, 1120, 1400 and 1800
Traverse speed(mm/min)	40
Length of weld(mm)	75
Axial Load(KN)	5

 

Fig.2 Tensile test specimens                                                                         Fig. 3 Taper profile tool geometry

 

The standard EN-AW 5083 aluminum alloy with chemical composition in  mass fractions: 4.34%Mg, 0.51%Mn, 0.14%Si, 0.088%Cr, 0.28%Fe, 0.20%Zn, 0.013%Ti and the remaining Al, and temper O, was used for testing. The work piece sizes were 150mm×60mm×4mm. the physical and mechanical properties as per standards were calculated.

 

Fig. 4 while the plates were under friction stir processing

 

5. RESULTS AND DISCUSSIONS:

For each sample the following tests are conducted and the samples are made with the Friction stir welding of Aluminum alloy 5083.

 

i.         Impact test

ii.       Microstructure

iii.     Tensile test

iv.     Rockwell micro-hardness test

 

Fig. 5 Aluminium5083 plates after FSW

A. Tensile Test:

After Friction Stir welding all the specimens were tested to get the ultimate tensile strength. Four samples were tested for each combination of parameter and their best joint values were considered. All the results were plotted in the form of a bar chart ultimate tensile strength v/s Rotational speed, impact strength v/s rotational speed and Hardness v/s rotational speed as shown in fig 6. fig7. Fig8, respectively. From the results of tensile test it can be studied that the ultimate tensile strength of the friction stir welded joint has been influenced by the tool profile of the welding tool.

 

TABLE IV, MECHANICAL PROPERTIES AT VARIOUS TOOL ROTATION SPEEDS

Tool rotation speed(rpm)	Tensile stress (N/mm2)	Impact strength (Joules)	Hardness
900	81.865	20	82.33
1120	74.88	40	74
1400	219.838	24	68.33
1800	87.585	20	59.33

 

 

Fig. 6 Tool rotation speed Vs Tensile strength                                        Fig. 7 Tool rotation speed Vs Hardness

 

Fig. 7 Tool rotation speed Vs Hardness

 

 

Fig. 8 Tool rotation speed Vs %Elongation

 

From the above bar charts it is clear that the ultimate tensile strength is more at a tool rotational speed of 1400rpm, because the heat input is sufficient at that condition and the grains were recrystallized and equip-axed.

From the graph the percentage of Elongation is more for 1120rpm and that is 5.74%, and less for1400rpm.

The tensile strength obtained at moderate heat supply and by increasing the tool rotation speed at 1400rpm, it increased to 219.838N/m²

4) The percentage change in the tensile strength is found to be 15.62% by using Tapered unthreaded cylindrical shoulder tool as the welding speed increases from 900 to 1400rpm.

 

The best joint of friction stir welding of aluminium5083 among four plates is at 1400rpm and at a welding speed of 40mm/min.

 

Rockwell Micro hardness:

 

Fig. 9 micro-hardness specimens

 

Rockwell hardness test is made to check the hardness of the welded specimens. The micro hardness of Rockwell is achieved great at 900rpm and the value is 82.33Hv. And it is very nearer 1120rpm with the value of 74Hv.

 

TABLE V: RESULTS SHOWING MICRO-HARDNESS

Tool rotation speed (rpm)	Hardness value (Hv)
900	82.33
1120	74
1400	68.33
1800	59.33

 

Impact strength

Izod Impact test is done to test the sudden load strength of the welded zone at different tool rotation speeds.

 

 

Fig. 10Izod Impact test specimens

 

 

Fig. 11 Schematic sketch of Impact Specimen

 

From the table IV, it was observed that the charpy Izod impact strength maximum at 1400rpm.

 

Microstructure study.

The tool rotation speed is important factor because it can influence the microstructure grain size. The following observations were

1)   Microstructure Results - Effect of Welding on Structural Properties of AA5083 Assessment of structural properties at different zones of the weldments using optical microscope was carried out. Microstructure of base metal consists of fine grains of alloying elements dispersed in the matrix of Al solid solution. The figure(C) shows that the microstructure is having fine grains and the structure shows that the grains are equip-axed and equally spaced, grain size were obtained half of the base material.

2)   The microstructure consist of elongated grains and course inter metallic particles are obtained in case of tool rotation speed of 900rpm as compared to 1400rpm in correlation with Tensile strength properties, percentage of Elongation and Izod impact strength. Small sized grains crosswise over entire weld shows that, high friction input is responsible for heating the weld over the temperature of recrystallization, here the grain development takes place. Also the Uniform grain growth can be observed at 1120speed.The grain size is small at the top of the weld, which was in region of the tool shoulder.

3)   From the microstructure study the figure (D) shows a very high fine and smooth grain structure, i.e., the grain size approximately equal to the half the grain size of base metal.

 

 

 (A) 900rpm (100µm)                                                               (B) 1120rpm (100µm)                              (C) 1400rpm (100µm)

 

 

 (D) 1800rpm (100µm)

Fig. 13 Microstructure images at different rotation speeds

 

6. CONCLUSIONS:

For Aluminum 5083, at 1400 rpm, by using Tapered with cylindrical profile tool the mechanical properties obtained were optimum.

 

It has been observed that the variation in tensile strength occurs for different tool rotational speeds. The tensile strength is found to be grater at 1400rpm and less at 1120rpm. At 900rpm the top of the weld was completely rough surface and the weld bead shows a defect which is shown in figure, because of lack of penetration of tool near the tip of it, wormhole defect.

 

Assessment of structural properties at different zones of the elements using optical microscope was carried out. Microstructure of the joint is best at 1800rpm with fine grain structure.

 

Hence the defect free joint was obtained at 900rpm with better mechanical properties correlated with microstructure. Uniform grain growth can be at higher speed (1800rpm).

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13.   P. Satish Kumar Influence of Tool Revolving on Mechanical Properties of Friction Stir Welded 5083Aluminum alloy

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Received on 30.11.2018            Accepted on 28.12.2018 ©A&V Publications all right reserved Research J. Engineering and Tech. 2018;9(4): 380-386. DOI: 10.5958/2321-581X.2018.00051.X