Effect of Initial Microstructure on the Microstructural Evolution and Joint Efficiency of a WE 43 Alloy During Friction Stir Welding

The initial microstructure plays an important role in determining the spatial and temporal evolution of the microstructure during friction stir welding (FSW). The overall kinetics of microstructural evolution is location sensitive and the effect of the process strain, strain rate and thermal cycle creates complexities. In the present study, magnesium based WE43 alloy has been welded employing two different welding conditions. Joint efficiency has been subsequently evaluated. The results have been correlated with detailed microstructural information obtained from SEM and OIM-EBSD. The influence of microstructural evolution on strength has been analyzed. This framework provides an approach to maximize joint efficiency. Introduction The onset of many desirable features like fuel efficiency and high specific strength are driving Mg alloys towards potential structural applications in the future. Strengthening is often a key property for material selection in a majority of applications. As a result, the specific strength advantage of the Mg alloys over their counterparts has triggered intensive effort for their use in engineering applications. WE43 is currently touted to be one of the most promising Mg alloys due to its good elevated temperature properties, creep performance, flammability resistance and relatively higher strength [1,2]. However, welding of Mg alloys is a major challenge and limits the ability to fabricate large and complex components [3]. Therefore, joint efficiency can have significant impact on expanding its applicability towards various sectors in the near future. Extensive study on Al alloys and a lucid understanding of microstructural evolution during the friction stir process has been formulated and is available in the literature [4,5]. Starting from Al alloys, a variety of Mg alloys have also been studied. Feng et al. [6] studied the effect of friction stir processing(FSP) on an AZ91 alloy and reported the dissolution and breakup of coarse eutectic Mg17Al12 phase. Park et al. [7] demonstrated the importance of texture and related it to the mechanical properties of an AZ61 alloy subjected to FSP. Ma et al. [8] suggested that FSP plays the role of solution treatment in AZ91 and saves time. Cao et al. [9] reported values of 69-78% for joint efficiencies in an AZ31-H24 alloy with failure occurring predominantly between stir zone(SZ) and thermo mechanically affected 253 Friction Stir Welding and Proceesing VII Edited by: Rajiv Mishra, Murray W. Mahoney, Yutaka Sato, Yuri Hovanski, and Ravi Verma TMS (The Minerals, Metals & Materials Society), 2013