Relationship Between Microstructure, Strength, and Fracture in an Al-Zn-Mg Electron Beam Weld: Part II: Mechanical Chara
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INTRODUCTION
PRECIPITATION hardening aluminum alloys are commonly used for structural applications requiring high specific strength, particularly in all transportation sectors (such as automotive and aerospace). Many techniques exist for assembling such alloys. Although solid-state techniques such as friction stir welding appear very attractive to retain the potential for precipitation hardening in all the weld regions, 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). An extensive review of these different techniques, applied on different alloys, can be found in Reference 1. Among precipitation hardening aluminum alloys, the EN-AW 7020 is a medium strength Al-Zn-Mg alloy particularly suited to welding,[2–4] due to the absence of Cu addition and to the low quench sensitivity related to the relatively low solute content. 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. RAFAEL ESTEVEZ, Professor, is with the SIMAP Laboratory, Universite´ Grenoble Alpes, also with the CNRS, SIMAP, and also with the Universite´ Joseph Fourier, Saint-Martin-d’He´res, France. 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
Irrespective of the welding technique, the assembly of precipitation hardening aluminum alloys always results in a heterogeneous spatial distribution of mechanical properties. Depending on the welding technique (whether it implies fusion and subsequent solidification), on the presence of filler material, on the initial temper and possibility of postwelding heat treatment, the softest zones can be found in the weld nugget or in the heat-affected zone. Accounting properly for the presence of the weld in mechanical design is a complex problem. The elasto-plastic mechanical behavior of the weld assembly is the result of the spatial distribution of the constitutive laws of the different zones affected by the welding operation. In addition, describing the behavior until fracture requires the knowledge of the fracture mechanisms in the zone where damage will develop first (usually the softest zone of the assembly), which is coupled to the elasto-plastic behavior of the assembly, in particular throug
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