A Transient Thermal Model for Friction Stir Weld. Part II: Effects of Weld Conditions
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THERE is a wide range of fascinating questions related to understanding the relationship between welding conditions, thermal values (heat generation and temperature), microstructural evolution, and mechanical properties in friction stir welds (FSWs). In the past decade, many researchers[2–11] have studied this relationship. It was reported that rotation rate, advancing speed, and tool geometry exerted significant effects on the thermal values, microstructural evolution, and mechanical properties of the FSW joints. However, in the early stages, research results did not reach an agreement in the relationship between the welding conditions and the mechanical properties of the welds.[7–11] Lee et al.[7] and Lim et al.[8] reported that decreasing the welding speed and increasing the rotation rate decreased the strength and elongation of FSW 6061Al-T651 joints. However, Ren et al.’s study[9] indicated that the strength of the FSW 6061Al-T651 joints did not change significantly with the variation of the rotation rate. Scialpi et al.[10] reported that a shoulder with a fillet and a cavity produced the best FSW 6082Al joint, whereas Fujii et al.[11] pointed out that the tool geometry did not exert a remarkable effect on the mechanical properties of 6061Al-T651 joints. Recently, Liu and Ma[12] studied systematically the relationship between the FSW conditions, thermal cycles, microstructure, and hardness of the low hardness zone (LHZ) of FSW 6061-T651 aluminum alloys, and [1]
X.X. ZHANG, Postgraduate, B.L. XIAO and Z.Y. MA, Professors, are with the Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, People’s Republic of China. Contact e-mail: [email protected] Manuscript submitted October 18, 2010. Article published online May 14, 2011 METALLURGICAL AND MATERIALS TRANSACTIONS A
proposed a heat source zone–isothermal dissolution layer (HSZ-ITDL) model. To quest for better understanding of the FSW process, it is important to obtain the accurate and global information of the evolution history of temperature, microstructure, and mechanical properties. However, in-situ experimental measurements of the FSW process are limited. It is impossible even to measure the temperature in the stir zone (SZ) because of the intense plastic deformation. Fortunately, numerical modeling, which combines thermal, microstructural, and mechanical modeling, provides a suitable way to study the relationship between the welding conditions, thermal values, microstructural evolution, and mechanical properties of the welds. To do this, thermal modeling is the first and crucial step. In the past decade, many models,[13–28] including the finite element method, computational fluid dynamics, and analytical models, have been used to explore the heat generation and temperature distribution in FSW. However, the mechanism of the effects of various welding conditions on the thermal values is not so clear. Part I[29] has built a transient thermal model that considers the entire FSW process. It ha
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