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9/27/04

9:35 PM

Page 2439

Control of Residual Stresses Affecting Fatigue Life of Pulsed Current Gas-Metal-Arc Weld of High-Strength Aluminum Alloy P.K. GHOSH and ARITRA K. GHOSH The influence of pulse parameters on residual stresses of the gas-metal-arc (GMA) weld of a 10-mm-thick extruded section of high-strength Al-Zn-Mg alloy has been analyzed. The role of pulse parameters affecting the residual stresses of the weld joint has been studied by considering a summarized influence of pulse parameters defined by a dimensionless factor   [(Ib/Ip) ftb]. The reason for the variation in residual stresses of the weld joint with a change in  under different mean currents (Im) has been studied by correlating the extent of weld metal deposition and weld size with the . It is observed that the increase of  reduces the longitudinal and transverse stresses of the weld joint. The nature of variation in residual stresses of the weld joint with  shows an agreement to the trend of variation in its size with . In conformation of an earlier work, it is proposed that the use of a pulsed current gasmetal-arc welding (GMAW) at proper pulse parameters giving desired  may produce a weld joint having comparatively lower residual stresses with improved fatigue life than that of the weld joint produced by conventional GMAW process through its influence on weld size.

I. INTRODUCTION

HIGH quality of weld joints, especially under dynamic loading, is of utmost importance to assure their safe performance in long-run applications. The absence of discontinuity defects and the presence of microstructure having desired ductility in the weld and heat-affected zone (HAZ) primarily define a superior quality weld joint. However, in this regard, consideration of residual stresses is also very much important due to their significant adverse influence on distortion, fatigue, corrosion, and stress corrosion cracking properties[1,2,3] of the weld joint of high-strength materials. Hence, the presence of high residual stresses in the weld joint of high-strength Al-Zn-Mg alloy is not desirable due to its well-known susceptibility to fatigue and stress corrosion cracking. In this matter the weld region is comparatively more sensitive because of the presence of maximum tensile stresses at the weld center. In the Al-alloy weld deposit, the residual stresses primarily result from the shrinkage of weld metal[4,5] depending upon weld thermal cycle.[6,7,8] The distribution of residual stresses in the weld joint is generally heterogeneous in nature primarily due to unsmooth arcing and metal deposition in the arc welding process. However, in spite of all these situations, there exists a regular pattern of stress distribution in weld joint, which is generally of tensile nature being maximum at the weld center and compressive at a certain location of the HAZ of the base metal. It is well known that the use of pulsed current in the gasmetal-arc welding (GMAW) significantly affects the thermal behavior and characteristics of metal transfer and thus improves weld