Relationship Between Microstructure, Strength, and Fracture in an Al-Zn-Mg Electron Beam Weld: Part I: Microstructure Ch
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PRECIPITATION hardening aluminum alloys are widely used in applications where specific strength is of strong importance, and particularly in all transportation sectors (automotive, aerospace, etc.). Their strength, plasticity, and fracture behavior are all closely related to the size and spatial distribution of nanometre-size precipitates. Many techniques exist for assembling such alloys.[1] Although solid-state techniques such as friction stir welding appear very attractive to retain the potential for precipitation hardening in all the weld regions,[2] in many cases it remains desirable or necessary to use fusion techniques, such as gas metal arc welding (GMAW), metal inert gas welding (MIG), laser beam welding (LBW), or electron beam welding (EBW). A review of these different techniques, applied on different alloys, can be found in Reference 3. During fusion welding, the solute is completely re-distributed by the solidification process and subsequent cooling to room QUENTIN PUYDT, formerly Ph.D. Student with the SIMAP Laboratory, Universite´ Grenoble Alpes, 38000 Grenoble, France, also with the CNRS, SIMAP, 38000 Grenoble, France, and also with the CEA Valduc, 21120 Is-Sur-Tille, France, is now Research Scientist with the IRT M2P, Metz, France. SYLVAIN FLOURIOT and SYLVAIN RINGEVAL, Research Scientists, are with the CEA Valduc. FRE´DE´RIC DE GEUSER, Research Scientist, is with the SIMAP Laboratory, Universite´ Grenoble Alpes, and also with the CNRS, SIMAP. GUILLAUME PARRY, Associate Professor, and ALEXIS DESCHAMPS, Professor, are with the SIMAP Laboratory, Universite´ Grenoble Alpes, also with the CNRS, SIMAP, and also with the Grenoble Institute of Technology, Grenoble, France. Contact e-mail: [email protected] Manuscript submitted April 30, 2014. Article published online September 19, 2014 METALLURGICAL AND MATERIALS TRANSACTIONS A
temperature. In adjacent zones (heat-affected zones HAZ), the material is subjected to a solid-state heat treatment that also completely disrupts the distribution of solute and related possibilities for nanoscale precipitation. The resulting mechanical properties of the assembly follow the heterogeneity of microstructure, and soft zones are generally encountered in the assembly of precipitation hardening alloys. The location of the softest zone (in the weld nugget or in the HAZ), as well as the severity of the strength loss, depend on many parameters such as the presence and nature of filler material, the type of welding process and process parameters, the nature of the alloy (e.g., quench sensitivity) and geometry of the weld, or the application of a post-welding heat treatment. Moreover, a complete understanding of the mechanical properties of a weld assembly cannot be achieved simply by the characterization of the softest zone of the weld assembly. A detailed understanding of the spatial distribution of the microstructure and related mechanical properties is actually necessary, as the mechanical behavior during plasticity (and particularly the stress state) depends on the
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