Microstructure characteristics and mechanical properties of a 2A66 Al-Li alloy processed by continuous repetitive upsett
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e Teng Department of Metal Materials Science and Engineering, College of Materials Science and Engineering, Hunan University, Changsha, Hunan 410082, People’s Republic of China
Zheng Lu Institute of Aluminum and Magnesium Alloy, Beijing Institute of Aeronautical Material, Beijing 100095, People’s Republic of China; and Beijing Advanced Engineering and Application Research Center of Aluminum Materials, Beijing 100095, People’s Republic of China (Received 26 March 2016; accepted 1 June 2016)
Continuous repetitive upsetting and extrusion (CRUE) processing was performed to investigate its effects on microstructures, mechanical properties and texture characteristics of a 2A66 Al–Li alloy. The results show that the average grain size is effectively refined from initial as-extruded ;140 lm to ;4 lm after 3 CRUE passes. The grain refinement is the combined effect of continuous dynamic recrystallization and discontinuous dynamic recrystallization. The texture intensity tends to be weaker and new cube texture is gradually developed with increasing CRUE passes. In addition, the fraction of high angle grain boundaries increases to 86.37% after 3 CRUE passes. Tensile test results reveal that the ductility is greatly enhanced with modest reduction in strength after CRUE processing. The variation in mechanical properties may be mainly due to the decrease of dislocation density and weakening of texture.
I. INTRODUCTION
Al–Li alloys with promising properties, such as very low density, high stiffness, and improved specific strength, have stimulated researchers’ interest in space and aerospace applications. Nevertheless, low ductility and toughness, poor thermal stability, and especially high anisotropy of mechanical properties make Al–Li alloys less competitive as replacements for conventional aluminum alloys and limit their applications.1,2 These disadvantages are mainly attributed to microstructure-related problems such as the presence of crystallographic texture, as-extruded or as-rolled elongated grains and inhomogeneous distribution of the second phases.2,3 As is known to all, severe plastic deformation (SPD) has great potential in refining grains and improving mechanical properties. Unfortunately, SPD methods, such as accumulative roll bonding, high press torsion and equal channel angular pressing, usually produce materials with strong texture.4 Repetitive upsetting and extrusion (RUE), however, has several advantages over other SPD techniques: imposing higher strain per cycle, bringing about
Contributing Editor: Jürgen Eckert a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2016.235 J. Mater. Res., 2016
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stronger alternate shear stress and thereby achieving a more effective grain refinement and homogenous structure.5 In the past, RUE processing has been successfully used to produce metallic materials with ultrarefined grain structure and weakened texture. Finite element method was used to simulate RUE processing and it was demonstrat
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