Optimization of current parameters during variable polarity GMAW of magnesium alloy

Abstract

Magnesium alloy welding suffers from problems such as burn through and loss of alloying elements during conventional welding process due to high heat input. Variable polarity gas metal arc welding (VP-GMAW) features low heat input. Therefore, it is an attractive method for welding of magnesium alloy. However, the principles governing the correlations among welding current parameters, metal transfer modes, and bead formation are not well understood. Identifying optimal welding current parameters by trial and error is unrealistic. Therefore, peak current, base current, and negative current were selected as independent variables. Their impact mechanism on metal transfer and bead formation were investigated by experiments with high-speed photographs. Then, weld quality evaluation was conducted by a fuzzy comprehensive evaluation. A mathematical method was proposed to calculate optimal current parameters for VP-GMAW of magnesium alloy. In addition, a significant sequence of current parameters is obtained. The results indicate that almost defect-free weld joint is produced by the optimal welding current parameters. The significance sequence of current parameters on weld quality is negative current, peak current, and base current.