Modeling and analyzing the effects of heat treatment on the characteristics of magnesium alloy joint welded by the tungsten-arc inert gas welding

The objective of this paper is to present the mathematical models for modeling and analysis of the effects of heat treatment on the characteristics of magnesium alloy joint welded by the tungsten-arc inert gas (TIG) welding. The process of heat treatment adopts the tempering process with varying processing parameters, including tempering temperature and tempering time. The microstructure and mechanical properties of the welded joint are considered in the characteristic evaluation and explored by experiment. An experimental plan of the face-centered central composite design (CCD) based on the response surface methodology (RSM) has been employed to carry out the experimental study. The results of analysis of variance (ANOVA) and comparisons of experimental data show that the mathematical models of the value of the maximum tensile strength and elongation are fairly well fitted with the experimental values with a 95% confidence interval. In the tempering process, the microstructure of welded joint in the weld bead displays two main microstructures of hcp-alpha-phase Mg and bcc-beta-phase Mg17Al12. Results show that the average size and proportion of alpha-phase Mg grains decreases with the increase of the tempering time and temperature. But, the increase of the tempering time and temperature promote increasing the average size and proportion of beta-phase Mg17Al12 grains. An increase in both the high value of tempering temperature and tempering time leads to an increase of the maximum tensile strength. The values of the elongation increase with increasing in both the value of tempering temperature and tempering time. (C) 2011 Elsevier Ltd. All rights reserved.