The Evolution of the Nugget Zone for Dissimilar AA6061/AA7075 Joints Fabricated via Multiple-Pass Friction Stir Welding

Abstract

AA6061 and AA7075 aluminum alloys were successfully joined by using single-pass and multiple-pass friction stir welding techniques after which the effects on the nugget zone evolution from a second overlapping pass and its welding direction, were investigated. In comparison to single-pass friction stir welding, the application of a second overlapping pass prolonged the dynamic recrystallization time, and the grains of the nugget zone became finer with increased high angle grain boundaries. Moreover, reversing the welding direction of the second overlapping pass enhanced the vertical flow of materials, increasing the strain of the friction stir welding in the nugget zone. As a result, the efficiency of the grain refinement and mixture of dissimilar materials during the second overlapping pass were significantly elevated. The tensile strength of the nugget zone was improved after the second overlapping pass due to both the grain refinement and mechanical interlocking of the AA6061/AA7075 alloys. The nugget zone, which was fabricated via the multiple-pass friction stir welding technique using an opposite welding direction, exhibited a 23% increase in yield strength as compared to the sample using the single-pass friction stir welding technique.

Novel Technique for Design and Manufacture of Alternating Gradient Composite Structure of Aluminum Alloys Using Solid State Additive Manufacturing Technique

“…It is essential to consider that a multitude of research has been done on the FSW behavior of AA6061-T6 and AA7075-T6 aluminum alloys [ 29 , 30 , 31 , 32 , 33 , 34 , 35 ], each with its own set of suggested welding parameters. Even when working with identical materials, the welding parameters may dramatically differ depending on factors such as the weld orientation, plate thickness, and, most crucially, the tool’s geometry.…”

The Influence of the Mechanism of Double-Sided FSW on Microstructure and Mechanical Performance of AZ31 Alloy

“…The microstructure refinement was carried out through the recrystallization mechanism. According to the Hall-Petch equation, [34][35][36][37][38][39][40][41][42][43][44][45][46][47], the increment (∆σ) of the yield strength caused by grain refinement can be computed by Equation (3):…”

“…The welding joint experienced the FSW of the D process, which obtained the optimal strength (315 MPa). According to the Hall-Petch equation, [34][35][36][37][38][39][40][41][42][43][44][45][46][47], the increment (Δσ) of the yield strength caused by grain refinement can be computed by Equation ( 3):…”

“…Compared to the single-pass FSW, the application of a second overlapping pass prolonged the DRX time and the DRX became sufficient, resulting in further grain refinement [38,39]. Chen et al found that reversing the welding direction of the second overlapping pass enhanced the vertical flow, increasing the FSW strain in the NZ [40].…”

Regularities of Friction Stir Processing Hardening of Aluminum Alloy Products Made by Wire-Feed Electron Beam Additive Manufacturing

“…When processing aluminum alloys, quite positive results were obtained [12], including, after EBAM [13], with an increase in the tensile strength and yield strength but a decrease in ductility. Most often, to achieve satisfactory results, FSP is done in several passes [14], also in different directions [15]. As a result of FSP, the structure of metals significantly changes relative to the base metal, which is the main factor affecting the mechanical characteristics [16].…”