CO 2 laser beam welding of 6061-T6 aluminum alloy thin plate
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I.
INTRODUCTION
LASER beam welding is characterized by its high energy density and flexibility and has obvious advantages, such as high speed, low distortion, and ease of automation. These properties make laser beam welding suitable for welding aluminum alloys. In particular, since its low overall heat input minimizes weld fusion zone and heat-affected zone (HAZ), there is an advantage in applying laser beam welding to age-hardened aluminum alloys, which have a problem of softening of the HAZ.[1,2,3] However, difficulties of laser beam welding of aluminum alloys lie in their high reflectivities to laser beam, porosity formation, and vaporization of magnesium and zinc in the weld metal.[4–9] The possible sources of porosity have been reported to be hydrogen, metal vapor, and shielding gas.[7,8,9] It has also been reported that fully penetrated welds have less porosity than partly penetrated ones.[7] The extent of vaporization of magnesium decreases with increasing welding speed.[6] Although the causes of the problems arising in laser beam welding of aluminum alloys have been investigated, these problems have not been completely overcome. In spite of the difficulties, laser beam welding is considered to have a great advantage, particularly in fully penetrated single-pass welds of age-hardened aluminum alloys with high welding speed. In the present work, laser beam welding was applied to thin plates of age-hardened Al-Mg-Si alloy (6061-T6) using a 2.5-kW CO2 laser. Bead-on-plate and butt welds with full penetration were performed, and formation of porosity in the weld metal was investigated. Softening occurs in the welds of the age-hardened 6061-T6. Thus, aging after welding was carried out to recover the hardness of 6061-T6 laser AKIO HIROSE, Associate Professor, and KOJIRO F. KOBAYASHI, Professor, are with the Department of Manufacturing Science, Graduate School of Engineering, Osaka University, Osaka 565, Japan HIROTAKA TODAKA, formerly Student, Graduate School of Engineering, Osaka University, is Engineer with Toyota Motor Corporation, Nagoya, 471, Japan Manuscript submitted January 1, 1997. METALLURGICAL AND MATERIALS TRANSACTIONS A
beam welds, and its effect was compared with that in TIG welds to reveal an advantage of laser beam welding. Tensile strengths of the welded joints were measured. II.
EXPERIMENTAL PROCEDURE
The aluminum alloy studied in the present experiment is a 1-mm-thick plate of 6061-T6, whose chemical composition is listed in Table I. Bead-on-plate welding and butt welding were performed using a 2.5-kW CO2 laser. Dimensions of specimens were 1 3 100 3 100 mm and 1 3 100 3 50 mm for bead-on-plate welding and butt welding, respectively. Immediately before welding, the surfaces of the specimens were finished with a stainless steel wire brush and cleaned with acetone before and after the brushing. In butt welding, two different methods for finishing the groove surface were employed. One was cleaning the surfaces only with acetone without the brushing and the other was polishing the surfaces wit
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