Statistical Analysis to Optimize the Electromagnetic Stirring Parameters
Magnesium-based alloys have received considerable interest in the field of automotive, aerospace and electronics application due to their desired mechanical properties. The Mg-Al-Zn/Mn systems were developed and commercialized extensively in the early 20th century. These alloys offer a good combination of mechanical properties, reasonable corrosion resistance, low cost and high castablity. Typical commercial alloys include the AZ91, AZ61, AM50 and AM60. Studies indicated that many methods to prepare the unique non-dendritic microstructure have been developed.
Semisolid metal forming of nondendritic structures has been studied and practiced commercially for some decades. The aim of wide variety of different semisolid forming techniques in contrast with Traditional casting approaches (like:sand casting and permanent casting) reduction on macro segregation and surface cracking, porosity and hot tearing. The lower casting temperature decrease the costs of energy. use of the protective atmosphere, achieve maximum spheroidal semisolid structure with minimum entrapped second phase. Electro-magnetic stirring is required to enhance the nucleation rate and restrict the growth of primary particles and consequently lead to the formation of slurries with uniform and refined microstructure.
This technique, due to lack of oxidation and subsequent contamination of the melt followed by achieve globular microstructure, to be suitable process to obtain slurries of Mg alloys [9]. In electromagnetic stirring casting process, it is necessary to carry out the casting using optimized parameters to achieve the desired properties. To obtain the optimized parameters, the scientific method is to use optimization techniques. The most important electromagnetic semisolid stirring parameters which would control the semisolids casting outputs are stirring time, applied voltage, rotational frequency and cooling rate. There are available optimization approaches such as Response Surface Methodology (RSM) and Taguchi’s Robust Design Methodology (TRDM) to solve optimization problem.
Design of experiment (DOE) and statistical techniques are widely used to identify the optimal input parameters. Optimization of process parameters is the key step in the Taguchi method inachieving high quality without increasing the cost. This is because optimization of process parameters can improve performance characteristics. The optimal process parameters obtained from the Taguchi method are insensitive to the variation of environmental conditions and other noise factors. However, many researchers have presently employed TRDM based GRA effectively and proven its usefulness in various applications with regard to multi-response optimization problems. A good globular microstructure is characterized by a microstructure having minimum dendrite and maximum spheroidal particles.
This study aimed is to determine the optimum process parametric combination for good globular microstructure of the Mg -5. 5Al -0. 3Mn magnesium alloy in a semisolid condition after electromagnetic stirring process. The near optimal electromagnetic stirring process parameters (stirring time, rotational frequency and pouring temperature) is obtained using GRA by simultaneously considering multiple output parameters (shape factor, average particle size, particle density, average aspect ratio, roundness).
