Optimization of gas metal arc welding parameters to weld AZ31B alloy using response surface methodology

Abstract

In the present work, an effort has been made to optimize the external magnetic field (EMF) for mechanical properties of magnesium alloy AZ31B weld. Magnesium alloys have the potential to replace cold-rolled carbon steel (CRC) and hot- rolled carbon steel (HRC) from automotive manufacturing industries. It has good specific strength and low density compare to aluminum (Al) and iron (Fe). Its low melting and boiling point are the difficulties to get sound weld joints in high heat input fusion welding process. The design of experiments (DOE) based on the central composite design (CCD) has been used for analysis and optimization of the gas metal arc welds of magnesium alloy AZ31B. The effect of the external magnetic field(EMF) on the yield strength(YS), microhardness(H) and microstructure of weld samples studied. The optimal solutions of direct effect and interaction effect of process parameters like wire feed rate, welding speed, gas flow rate and external magnetic field are obtained by using Minitab-17 software. The insignificant terms related to the direct effect of process parameters or their interaction were removed from the mathematical model by backward elimination method. The change in microhardness at weld center is also critically analyzed. The direct effect of EMF on yield strength in comparison to other process parameters is 1% to 4%. The EMF 120 Gauss showed significant improvement in yield strength. At 120 Gauss; predicted optimum yield strength as 138 MPa and experimentally obtained mean yield strength is 137 MPa i.e. 96% of base metal with the significant increase in microhardness up to 100 HV at the weld center. The other variables kept constant as 5.7 m/min wire feed rate, 700 mm /min welding speed and 11 Ltr /min as gas flow rate. The study of changes in surface morphology is analyzed using field emission scanning electron microscopy. The fine grains with no traces of weld cracks and porosity are observed under the effect of the external magnetic field.