EFFECT OF PROCESS PARAMETERS ON THE …

1 Journal of engineering Science and Technology Vol. 10, No. 6 (2015) 790 - 801 School of engineering , Taylor s University 790 EFFECT OF PROCESS PARAMETERS ON THE tensile strength OF FRICTION STIR WELDED DISSIMILAR ALUMINUM JOINTS R. PADMANABAN1,*, V. BALUSAMY2, K. N. NOURANGA1 1 Amrita School of engineering , Amrita Vishwa Vidyapeetham, Coimbatore, Tamilnadu, India College of Technology, Coimbatore, India *Corresponding Author: Abstract Friction stir welding is one of the recent solid state joining processes that has drawn the attention of the metal joining community. In this work the effects of tool rotation speed (TRS) and welding speed (WS) on the tensile strength of dissimilar friction stir welded AA2024-AA7075 joints are investigated.

2 Response surface methodology is used for developing a mathematical model for the tensile strength of the dissimilar aluminum alloy joints. The model is used to investigate the EFFECT of TRS and WS on the tensile strength of the joints. It is seen that the tensile strength of the joint increases with the increase in TRS up to a limit of 1050 rpm and decreases thereafter. The tensile strength of the joints is also seen increasing with the WS up to 15 mm/min. Further increase in WS results in a reduction of the tensile strength of the joints. Keywords: Friction stir welding, tensile strength , Mathematical model, Response surface methodology. 1. Introduction Friction stir welding (FSW) is a solid state joining PROCESS invented at The Welding Institute, Cambridge by Thomas et al.

3 [1]. FSW has enabled the joining of materials that were considered difficult to be joined by conventional processes. The PROCESS uses frictional heat to join two materials that are in the form of plates. The basic principle of the FSW PROCESS is illustrated in Fig. 1 [2]. In this PROCESS , a rotating tool with a profiled pin is slowly inserted into the abutting edges of the plates and then moved along the length of the joint. The material under the tool is plastically deformed and it flows around the tool. As the tool moves forward, the material behind the tool cools down and a joint is formed in the solid state. EFFECT of PROCESS PARAMETERS on the tensile strength of Friction Stir .. 791 Journal of engineering Science and Technology June 2015, Vol.

4 10(6) Nomenclatures b0, b1, .. Coefficients of regression equation Abbreviations SD TRS Standard Deviation Tool Rotation Speed TS tensile strength WS Welding Speed Fig. 1. Schematic of Friction Stir Welding. The PROCESS has numerous advantages which make it a preferred choice in a number of industries and for futuristic applications as detailed by Mishra and Ma [2]. The FSW PROCESS PARAMETERS play a primary role in deciding the strength and efficiency of the joints. The tool rotation speed (TRS) and welding speed (WS) are two important PARAMETERS influencing joint characteristics. The EFFECT of these PARAMETERS on temperature distribution, material flow, microstructural evolution and mechanical properties decide the PROCESS window boundaries for a given material.

5 FSW, ever since its invention has been extensively studied by researchers. Liu et al. [3] bring out the relation between welding PARAMETERS and tensile properties of AA2017-T351. Peel et al. [4] examine the microstructure and mechanical properties of friction stir (FS) welded aluminum alloy AA5083 under different conditions. Lim et al. [5] explore the influence of TRS and WS on the tensile behaviour of friction stir (FS)Welded AA6061-T651 alloy. Minton and Mynors [6] present a methodology for determining the PROCESS window for a given material. Sheikhi and Dos Santos [7] study the influence of welding PARAMETERS and welding tools on weld quality and mechanical properties of tailor welded blanks of AA6181-T4.

6 Elangovan and Balasubramanian [8] examine the EFFECT of different tool pin profiles and shoulder diameters on the formation of friction stir processing zone in AA6061 aluminum alloy. Liu and Ma [9] get AA6061-T651 FS welded joints under different PROCESS PARAMETERS and tool dimensions. 792 R. Padmanaban et al. Journal of engineering Science and Technology June 2015, Vol. 10(6) Rajamanickam and Balusamy [10] study the EFFECT of TRS and WS on temperature distribution and mechanical properties of FS welded aluminum alloy AA2014. Elangovan et al. [11] develop a mathematical model, incorporating FSW PROCESS PARAMETERS , to predict the tensile strength of friction stir welded aluminium alloy AA2219.

7 Rajakumar and Balasubramanian [12] investigate the properties of FS welded joints made using six different grades of aluminium alloys. The joining of dissimilar materials is now becoming an inevitable requirement in many engineering applications and as such studies on joining of dissimilar materials is gaining momentum significantly. FSW paves the way for joining materials difficult to be joined by conventional methods. For example, in the case of automotive components, there is a need to weld aluminum and steel, which is practically impossible using conventional fusion welding techniques. Murr [13] presents a review that summarises FSW of similar and dissimilar material systems.

8 Khodir and Shibayanagi [14] examine the EFFECT of welding speed and location of base materials on microstructure, hardness distributions and tensile properties of dissimilar FS welded joints of AA 2024-T3 and AA7075-T6. DaSilva et al. [15] investigate the EFFECT of joining PARAMETERS on tensile strength , hardness, material flow and microstructure of dissimilar FS welded joints between AA2024-T3 and AA7075-T6. Bahemmat et al. [16] study the EFFECT of FSW PARAMETERS on the weldability, mechanical properties and grain size of FS welded dissimilar aluminum alloys AA2024-T4 and AA7075-O. Aluminum alloys of dissimilar combinations are required to be joined for many industrial applications.

9 The 2xxx (Al-Cu) and 7xxx (Al-Zn-Mg) series alloys have potential application in modern and future aircrafts [17]. Of late, the skin and stringers in aircrafts (made of AA7075 and AA2024 respectively) are invariably joined using FSW. These alloys are difficult to be welded using arc welding processes due to hot cracking and stress corrosion cracking. Hence it is worthwhile to study and evaluate FSW PROCESS applied to these alloys. It can be seen from the aforesaid discussions that work done in this area are a few. So further investigation on FSW of these two dissimilar materials is surely worthwhile. Response surface methodology is used to develop a mathematical model for the tensile strength of AA2024 and AA7075 dissimilar joints.

10 The developed model is used to study the EFFECT of PROCESS PARAMETERS on the tensile strength of the joints. 2. Experimental Procedure AA2024 and AA7075 plates each of size 150 60 5 mm are friction stir welded using a vertical milling centre shown in Fig. 2. The mechanical properties of the base materials are given in Table 1. The fixture for holding the aluminum plates during the FSW trials is made of mild steel plate of thickness 20 mm. A cylindrical threaded tool made of high speed steel, with a shoulder diameter of mm, pin diameter of 5 mm and height mm is used for the trials. The tool is fabricated using turning and thread grinding processes and no heat treatment is given to the tool.