Process Optimization of Dual-Laser Beam Welding of Advanced Al-Li Alloys Through Hot Cracking Susceptibility Modeling
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THE newly developed lithium-bearing 2xxx series aluminum alloys have shown great potential for aerospace applications due to their high specific strength plus high stiffness. It is known that every 1 pct (wt) of lithium blended into aluminum increases the elastic modulus by about 6 pct and reduces the density by about 3 pct at the same time.[1] The recently developed Li-bearing AA2198 and AA2196 aluminum alloys are very promising high-strength and light-weight alloys for aircraft manufacturing, for example, the skin-stringer T-shaped joints for fuselage panels. There is a strong motivation in the aerospace industry to use laser beam welding to manufacture skin-stringer structures due to the weight saving by replacing the traditional riveted structure with a welded component. However, Li-bearing aluminum alloys typically present severe weldability issues of high
YINGTAO TIAN and LI WANG, Research Associates, and JOSEPH D. ROBSON, Professor, are with School of Materials, The University of Manchester, M13 9PL, Manchester, UK. Contact e-mail: [email protected] STEFAN RIEKEHR, Materials Scientist, and NIKOLAI KASHAEV, Head of Department, are with the Institute of Materials Research, Materials Mechanics, HelmholtzZentrum Geesthacht, Max-Planck-Str. 1, 21502 Geesthacht, Germany. TRISTAN LOWE, Experimental Officer, is with Henry Mosely X-ray Imaging Facility, School of Materials, University of Manchester, Manchester, UK. ALEXANDRA KARANIKA, Project Leader, is with Research and Product Design, Hellenic Aerospace Industry S.A., P.O. Box 23, 32009 Schimatari, Greece. Manuscript submitted December 14, 2015. METALLURGICAL AND MATERIALS TRANSACTIONS A
hot cracking susceptibility (HCS) in the joints.[1–4] Hot cracking, also referred as hot tearing or hot shortness, occurs during the solidification of the welding pool in the temperature range above solidus, which can cause a failure of the joint immediately after welding or initiate a fatigue crack during the service. Therefore, understanding and minimizing hot cracking is critical to achieving good quality joints. At present, the only way to find a set of processing parameters and weld filler chemistry that avoids hot cracking is through trial and error experimentation. This is inefficient with no guarantee that an optimum parameter set will be deduced. There is thus a strong motivation to develop a simulation tool that can predict HCS and guide the selection of the best parameters for welding. Furthermore, a physics-based model can help in understanding the factors that contribute to hot cracking, and thus guide future alloy and filler wire development. The objective of the present work was to develop a physics-based model to predict HCS in Al-Li laser welds and validate the model against results from experimental welds performed under a range of conditions. Hot cracking models in the literature have typically been developed to predict HCS in castings. Since casting and welding both involve liquid metal solidification, such models can be adapted to deal with HCS in welds.
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