Correlation Between Texture Variation and Transverse Tensile Behavior of Friction-Stir-Processed AZ31 Mg Alloy
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INTRODUCTION
FRICTION stir welding (FSW) was invented as a solid-state joining technique at the Welding Institute of the United Kingdom in 1991.[1] Since its invention, many studies have shown that FSW is advantageous to weld light structural materials such as Al and Mg alloys.[2–6] Lately, based on the basic principles of FSW, Mishra et al.[7] and Ma[8] developed a friction stir processing (FSP) technique primarily for microstructural modification. For the FSP technique, it is known that a specially designed rotating tool is inserted in a material for localized microstructure and texture modification. It has been demonstrated that FSP is an effective means of refining grain size of light metals via dynamic recrystallization.[8,9] Among the light metals investigated, the Mg alloy is receiving increasing research attention because of its potential application in transportation.[10,11] In previous studies, the microstructure and texture evolutions in friction-stir-welded or processed Mg alloy have been extensively investigated. For example, Esparza et al. investigated characteristic grain structures such as the stir zone (SZ), transition zone (TZ), and base material (BM) in friction-stir-welded AZ31B Mg alloy.[12] Park et al. observed a localized strong texture development in RENLONG XIN, Professor and Doctoral Tutor, ZHENG ZHOU and QING LIU, Professors, are with the College of Materials Science and Engineering, Chongqing University, Chongqing, P.R. China, and are also with the National Engineering Research Center for Magnesium Alloys, Chongqing University, Chongqing, P.R. China. Contact e-mail: [email protected] BO LI and AILIN LIAO, Postgraduate Students, are with the College of Materials Science and Engineering, Chongqing University. Manuscript submitted May 5, 2011. Article published online March 8, 2012 2500—VOLUME 43A, JULY 2012
friction-stir-welded AZ61 Mg alloy and suggested that the basal plane is roughly aligned with the tool pin surface in the SZ.[13] The mechanical properties of friction-stirwelded or processed Mg alloy were also studied.[14,15] For instance, Chang et al.[16] and Wang et al.[17] reported that the hardness profile in friction-stir-processed AZ31B Mg alloy exhibited weak grain size dependence in terms of the classic Hall–Petch relationship. This was ascribed by Yang et al. to grain refinement simultaneously inducing texture variation in friction-stir-welded Mg-3Al-1Zn alloy.[18] Woo et al. carried out quantitative texture changes in friction-stir-processed AZ31B and reported reduced yield strength and increased elongation along the longitudinal direction in the SZ.[19] From the previous studies, it is seen that changes in microstructure and especially texture have significant influence on the mechanical properties of Mg alloy. However, how the texture variation in friction-stirwelded or processed Mg alloy affects the activation of slip and twinning and, hence, influences the mechanical behavior is not well understood. Moreover, although the texture of friction-stir-processed Mg alloy has been quantita
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