J. Manuf. Sci. Prod., Vol. 12 (2012), pp. 111–118 Copyright © 2012 De Gruyter. DOI 10.1515/jmsp-2012-0008 Multi Objective Optimization of Friction Stir Processing Parameters on Mg AZ31B Alloy Using Grey Relational Analysis Ganta Venkateswarlu, 1; M. Joseph Davidson, 1 Gogi- neni Ravindranath Tagore 1 and Pulla Sammaiah 2 1 Department of Mechanical Engineering, NIT Warangal 2 Department of Mechanical Engineering, S. R. Engineer- ing college, Warangal Abstract. This paper presents the multi-response optimi- sation of friction stir processing (FSP) process of AZ 31 Mg alloy for an optimal parametric combination to yield max- imum tensile strength and elongation using Taguchi and Grey relational analysis (GRA). In this study, the FSP pro- cess parameters such as rotational speed, traverse speed and tool tilt angle have been selected. The experiments were planned using Taguchi parametric design L 9 with various combinations of process parameters. Statistical technique ANOVA was used to determine percentage of contribution of process parameters. Optimal results have been verified through confirmation experiments. The results indicate that rotational speed has more effect on responses followed by traverse speed and tool tilt angle. In addition, mathematical models were developed to establish relationship between different process variables and outcomes. Keywords. Friction stir processing, Taguchi, Grey rela- tion. PACS ® (2010). 60. 1 Introduction In recent years, the magnesium products have been attract- ing more and more attention in automotive applications be- cause of their favourable characteristics of light weight, re- cycling and high specific strength [1]. However, the use of magnesium alloy has been strongly limited in forming because of poor ductility and formability at room tempera- ture as a result of hip lattice structure. AZ31B magnesium alloy is commercially available in sheet form, and offers good properties, but this alloy exhibits very limited ductility at room temperature. However, the recent results indicate * Corresponding author: Ganta Venkateswarlu, Department of Mechanical Engineering, NIT Warangal, A. P., India-506004; E-mail: ganta_hmp@rediffmail.com. Received: May 31, 2012. Accepted: June 22, 2012. that it is possible to improve the ductility and formability of magnesium sheet at elevated forming temperatures under certain conditions [2]. The results also proposed that im- proved mechanical properties could be attained by refining and homogenizing the grain structure of the sheet. Friction stir processing is an emerging surface- engineering technology developed based on the principles of friction stir welding. FSP eliminates casting defects and refines microstructures, thereby improves strength and duc- tility [3–6]. Friction stir processing has been successfully applied to many aluminium alloys in improving mechanical properties [7–9]. But very limited work has been carried out on friction stir processing of magnesium alloys. Sato et al. [10] determined the effect of FSP on microstructure of AZ91 magnesium alloy and observed that more grain re- finement and homogenization when compared to the cast properties. Taguchi methods are statistical methods developed by Dr. Gnocchi Taguchi; refer to quality engineering tech- niques that incarnate both statistical process control (SPC) and new quality related management techniques. Taguchi method uses orthogonal arrays from design of experiments theory to study a large number of variables with a small number of experiments. Orthogonal arrays are not unique to Taguchi. They were found out considerably earlier. How- ever, Taguchi has modified their use by providing tabulated sets of standard orthogonal arrays and corresponding lin- ear graphs to fit specific projects. The experimental results are then transformed into a signal-to-noise (S=N) ratio. It uses the S=N ratio as a measure of quality characteristics deviating from or nearing to the desired values. There are three categories of quality characteristics in the analysis of the S=N ratio, i.e. the lower-the-better, the higher-the-better, and the nominal-the-better. The S=N ratio for each param- eter is worked out based on S=N analysis. Irrespective of the quality characteristics, a larger S=N ratio corresponds to better quality characteristics. Therefore, highest S=N ratio is the optimal level of each process parameter. In this study, three controlling FSP process parameters were selected and optimized trough Grey relational method by analysing Gray relational grade matrix. Additionally a statistical technique analysis of variance (ANOVA) was also used to examine the most significant factors for the tensile strength and elonga- tion of FSPed Mg AZ 31 alloy. Brought to you by | New York University Bobst Library Technical Services Authenticated Download Date | 6/3/15 6:14 PM