Investigation on the microstructure and mechanical properties of a dissimilar friction stir welded joint of magnesium alloys

Abstract

In the current scenario, the light-weighting concept is the most important strategy to decrease fuel consumption as well as emissions of greenhouse gases. Magnesium alloys are attractive to various industries including transportation industry for their inherent light-weight. The friction stir welding is proficient to join magnesium alloys. In this article, a dissimilar friction stir welding butt joint between AZ31 and AZ61 magnesium alloys was fabricated, and microstructure and mechanical properties have been examined. The tool rotation speed of 1400 r/min and tool transverse feed rate of 25 mm/min was found quite suitable to fabricate a perfect joint of these dissimilar magnesium alloys. The stir zone was composed of fine and equiaxed grains and showed the highest microhardness value. In the advancing side, heat affected zone was composed of both equiaxed and elongated grains; however, in the retreating side, heat affected zone has relatively smooth grains. The tensile strength of the joint was about 138.37 ± 6.6 MPa. The efficiency of the joint was 51.25% with respect to AZ61 Mg alloy. The average impact toughness of friction stir welding joint was deteriorated by 16.67% and 28.5% with respect to base materials AZ31 and AZ61, respectively.

Influence of post welding heat treatment on the microstructure and mechanical properties of friction stir welding joint of AZ31 Mg alloy

“…This way, FSW joint exhibited lower toughness (about 20%) than base metal. Similar observations have been reported by Singh et al 43 and Ugender et al 54 In contrast, Singh et al 49 reported higher impact toughness of FSW joint than toughness of base metal AZ31B-O Mg alloy. Post welding heat treatment process further reduced the impact toughness of the joint.…”

“…This is consistent with results reported for aswelded joint in earlier research. 43,50 Failure location of tensile specimens remained unchanged after post welding heat treatment (see Supplemental Figure 5).…”

“…Evolution of fine and equiaxed grains within stir zone have been reported by other researchers. 43,44 Thermomechanically affected zone (adjacent to stir zone) also experienced deformation and heat which resulted in equiaxed grains in this zone. Due to material deformation and huge frictional heat, it is expected that TMAZ undergone recrystalization.…”

“…It was also in agreement with previous results of FSW joints failure during tensile test. 17,43 After post welding heat treatment, tensile strength of joint was about 152.4 AE 9.5 MPa and elongation was about 11 AE 0.7%. This way, tensile strength and elongation of joint were improved by 4.74% and 15.78% respectively after PWHT.…”

Study of optimum welding performance in friction stir welding of dissimilar Mg alloys using integrated RSM-TLBO algorithm

“…To overcome difficulties associated with fusion welding of Mg alloys, Friction Stir Welding (FSW) is the best alternative. 10 FSW process has been used for welding of similar 4,8,10,11 as well as dissimilar Mg alloys, 7,12 Aluminium alloys, 13,14 and Aluminium-Copper.. 15 Friction Stir Welding is a solid-state welding process invented in 1991 by Thomas et al 16 at The Welding Institute (TWI). In FSW, a rotating tool, having predefined geometry, is inserted inside the workpiece material until its shoulder touches the workpiece and allowed to rotate for a definite time period known as dwell time and then moved along the weld joint to produce weldment.…”