Quantitative evaluation of softened regions in weld heat-affected zones of 6061-T6 aluminum alloy—Characterizing of the laser beam welding process

Abstract

In welding 6061-T6 aluminum alloy, softening caused by the dissolution of strengthening ␤ Љ (Mg 2 Si) precipitates occurs in heat-affected zones (HAZs). Laser beam welding is advantageous in view of narrower softened regions. The width of the softened region in a laser beam weld with a welding speed of 133 mm/s is 1/7 that of a tungsten inert gas (TIG) weld with a speed of 5 mm/s. The hardness distributions and width of softened regions in the HAZ have been quantitatively predicted to characterize the laser beam welding process. To this end, a kinetic equation describing the dissolution of age precipitates has been established and has been applied to 6061-T6 aluminum weldments. The hardness profiles and the width of softened zones have been successfully predicted in both welding processes. Prediction of the width of softened regions with varying power inputs and welding speeds reveals that a high energy density and a high welding speed in laser beam welding result in significantly narrower softened regions, in which the width is insensitive to variations in welding parameters compared to that of TIG welding.

Tensile fracture behavior in CO2 laser beam welds of 7075-T6 aluminum alloy

“…As a result, tensile failure is obtained in the FZ. The hardness drop in the HAZ of the GTA weld is caused by insufficient strengthening in the matrix of this region due to precipitation of non-hardening phases during weld thermal cycle [25].…”

Research and Progress in Laser Welding of Wrought Aluminum Alloys. II. Metallurgical Microstructures, Defects, and Mechanical Properties

“…Hirose et al [9,10] measured the widths of the softened region in the HAZ of CO 2 laser -welded 6061-T6 sheet material of 1-mm thickness. The softened region is defined as the region where hardness values fall below 90% those of the base metal.…”

“…Their results showed that the widths of softened regions in the HAZs of the laser welds are of the order of one seventh to one quarter those for TIG welds. [9,10] Although the HAZs of laser-welded joints are very narrow, many solid-state reactions such as grain growth and precipitate coarsening may occur in the zone. [11] In non -heat-treatable Al alloy, softening occurs because of localized annealing in the HAZ by grain growth or loss of strain-hardened structure.…”

Effect of pulsed Nd:YAG laser re-melting on chromium surface alloyed AA6061-T6 aluminum

“…However, the hardness of heat-affected zone (HAZ) was decreased to 80 HV. It has been reported that during surface melting of AA6061-T6 aluminum, strengthening Mg 2 Si precipitates formed by T6 solution-aging heat treatment on 6061 aluminum dissolve in the aluminum matrix in the heat-affected zone [30,31]. Figure 10 shows the hardness maps along the polished top surface of the as-alloyed and re-melted layers.…”