Microstructure and Mechanical Behavior of Friction Stir-Welded Sc-Modified Al-Zn-Mg Alloys Made Using Different Base Met
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Microstructure and Mechanical Behavior of Friction Stir-Welded Sc-Modified Al-Zn-Mg Alloys Made Using Different Base Metal Tempers Jiqiang Chen, Shengci Li, Hailong Cong, and Zhimin Yin (Submitted May 13, 2018; in revised form December 9, 2018; published online January 22, 2019) The microstructure and property of friction stir weld joints of a Sc-modified Al-Zn-Mg alloy developed using base metal in hot-rolled (HR) and T6 temper were studied and compared in this work. The results showed that the microstructure and property exhibited significant difference between the two friction stir weld joints. The weld efficiency of the FSW joint developed using base metal in HR condition is over 90%, while that of the FSW joint developed using base metal in T6 condition is only 70%. The hardness of the weld nugget of HR joint is obviously higher than that of the weld nugget of T6 joint, due to the different changes in the original precipitates during the friction stir welding process. The strengthening mechanism in different zones of the two FSW joints was discussed to examine the microstructure–properties relationship, and the main difference of the strengthening mechanism between the two FSW joints was revealed. Keywords
Al alloy, friction stir welding, precipitates, property, Sc
1. Introduction The Al-Zn-Mg alloy has been widely used in aerospace applications for decades, due to the good combination of specific strength, hot workability, toughness and fatigue durability (Ref 1). Al-Zn-Mg-Sc alloys are designed based on Al-Zn-Mg alloys to improve the mechanical properties by adding a small amount of Sc. In addition, a small addition of Sc could generate a fine grain structure (Ref 2) and provide higher recrystallization temperature (Ref 3), due to the precipitation of high dispersivity of Al3Sc particles in the matrix. The Scmodified Al-Zn-Mg alloy has attracted many interests in aerospace and military applications. Al-Zn-Mg alloys are generally joined by fusion welding techniques in numerous application fields, such as automobile, railway, aviation and so on (Ref 4). However, fusion weld joints exhibit relatively low ductility and tensile strength, as well as the poor resistance to fatigue failure. The friction stir welding (FSW) is a relatively new ‘‘solid-state’’ joining technique that prevents solidification problems, and it is also potential to be used in materials that are traditionally considered to be unweldable. FSW was first introduced in 1991 by The Welding Institute (TWI) (Ref 5). It is nowadays a well-known welding technique and has been widely investigated for numerous alloys. A number of investigations (Ref 6-10) for the comparJiqiang Chen, Shengci Li, and Hailong Cong, School of Materials Science and Engineering, Jiangxi University of Science and Technology, Ganzhou 341000, China; Zhimin Yin, School of Materials Science and Engineering, Central South University, Changsha 410083, China. Contact e-mail: [email protected].
916—Volume 28(2) February 2019
ison of conventional TIG weld
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