Influence of Post-Laser Welding Heat Treatment on Assembling Performance of Aluminum Alloy Structure
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DURING the past few decades, laser beam welding has been used and considered as an efficient process for assembling structures, particularly aluminum alloy structures.[1–4] However, various improvements relating to this processing method could be made depending on the nature of the alloy and the assembly geometry. More specifically, performance of assemblies is directly dependent on bead performance, the composition of which is controlled by processing conditions. For instance, welded structures made of ductile aluminum alloy may seem brittle when the failure strength of the bead is too low, compared to the yield strength of the surrounding base alloy, to enable the structure to flow. Consequently, one of the objectives for adjusting the processing conditions is to increase bead strength, either thanks to a suitable choice of metal filler, or through modification of the laser power and welding speed or even through post-weld heat treatments (PWHT). Several studies reported in the literature are devoted to the influence of fusion zone (FZ) composition on bead performance. The latter can be controlled by the nature of the metal filler, or by the ratio between the filler and welding speeds or even by the size of the FZ, that is to say by ‘‘keyhole’’ or ‘‘conduction’’ welding.[5] Although, this aspect related to FZ composition is very important because it determines not only bead strength but also the hot cracking resistance of the bead, the GUILLAUME TIRAND, Ph.D. Student, is with Univ. Bordeaux, I2M, UMR 5295, Site IUT 15, rue Naudet, CS 10207, 33175 Gradignan, France, and also with the ASTF (Ae´ro Service Toˆlerie Fine) Groupe ALCEN, 33692 Me´rignac, France. CORINNE ARVIEU, Associate Professor, ERIC LACOSTE, Professor, and JEAN-MICHEL QUENISSET, Professor, are with Univ. Bordeaux, I2M, UMR 5295. Contact e-mail: [email protected] Manuscript submitted July 19, 2012. Article published online September 27, 2013 METALLURGICAL AND MATERIALS TRANSACTIONS A
present paper will not be focused on this aspect which will be the topic of a further contribution elsewhere.[6] In the present contribution, for given metal filler and conditions of laser welding, the influence of PWHT on bead performance is investigated, even if a number of PWHT for improving bead performance and thus enabling assemblies to exhibit large deformation before rupture, have been already proposed elsewhere.[7] Considering Al-Mg-Si alloys (6000 series), which are of great interest in the aeronautical industry, the heat treatment generally performed after welding such as laser welding is a single or a double aging heat treatment (SAHT or DAHT) which tends to harden the heat affected zone (HAZ) and raises the yield strength of the FZ.[8] However, it is shown in the present contribution that although this type of post-weld DAHT exhibits some efficiency, the increase in bead strength related to the DAHT, is insufficient to enable the extension of the whole welded structure before failure. Thus, after evaluating the effects of direct post-weld single aging hea
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