A Comparative Study on Fatigue Response of Aluminum Alloy Friction Stir Welded Joints at Various Post-Processing and Treatments

Abstract

The present study examines the fatigue of friction stir welded (FSW) aluminum 6061, 7075, 1060 joints followed by (i) in situ and sequential rolling (SR) processes, (ii) plastic burnishing (iii) solution-treatment artificial aging (STA), (iv) local alloying through depositing thin copper foils, and (v) inserting alumina powder in the weld nugget zone (NZ). The microstructural features and fatigue life of post-processed joints were compared with those of as-welded joints. The in situ rolling technique offered simultaneous rolling and welding operations of aluminum joints, while through the sequential rolling process, the top surface of FSW joints was rolled after the welding process. The fatigue life of in situ rolled samples was increased as the ball diameter of welding tool increased. The fatigue life of friction stir welded joints after a low-plasticity burnishing process was noticeably promoted. The addition of 1 wt.% alumina in the NZ of joints resulted in a significant elevation on fatigue life of friction stir spot welded joints, while an increase in alumina powder to 2.5 wt.% adversely affected fatigue strength. Weld NZ was alloyed through the insertion of copper foils between the faying surfaces of joints. This localized alloy slightly improved the fatigue life of joints; however, its effects on fatigue life were not as influential as STA heat-treated or in situ rolled joints. The microstructure of weld joints was highly affected through post-processing and treatments, resulting in a substantial influence on the fatigue response of FSW aluminum joints.

Friction Stir Welding of Non-Heat Treatable Al Alloys: Challenges and Improvements Opportunities

“…It was observed that copper foil with a thickness of 100 µm resulted in higher tensile strength (101 MPa) than 200 µm thickness (88 MPa). The thicker copper foil caused the excessive formation of the brittle intermetallic compound in the stir zone [167]. The positive effect of TiC nanoparticles on the transverse tensile strength of dissimilar FSW between AA5083-H111 and AA6082-T6 was also suggested [162].…”

“…The additions of various reinforcement particles have been introduced as an improvement strategy for increasing the mechanical properties of FSWed joints of strain-hardened Al alloys. For instance, the effects of TiC [162], TiO 2 [163], and SiC [164] nanoparticles, Cu and pre-mixed Cu-Al Powder [56,165], Al 3 Sc compound [166], and inserting Cu foils [167] on the mechanical properties of FSWed joints of Al alloys have been previously investigated. All of these studies have unanimously reported that the incorporation of reinforcement particles into the gap between two sheets strengthens the stir zone's mechanical properties, provided that appropriate welding parameters are chosen.…”

“…Under these circumstances, the uniform and symmetrical distribution of particles are formed, and the agglomeration of particles is considerably reduced in the weld zone. Moreover, it is beneficial for the formation of more in situ intermetallic reinforcement due to proper interaction between particles and the Al matrix [56,163,165,167].…”

“…Furthermore, Hassanifard et al [167] performed FSW on AA1060-H16 by inserting thin Cu foil with a thickness of 100 and 200 µm between two sheets. Based on their report, the transverse tensile strength was increased by inserting both 100 and 200 µm Cu foil compared to an as-welded sample (without Cu foil).…”

Effect of Sheets’ Thickness and Rivet Geometry on Mechanical Properties of Orbital Riveted Aluminium Joints: Experimental and Numerical Analysis

“…In this context, several innovative solutions for joining aluminium sheets have emerged in recent decades, i.e., friction stir welding [3,4], self-piercing riveting [5], clinching [6], and orbital/planetary riveting [7]. In particular, orbital riveting is a cold-forming process that gives good results at a lower cost [8].…”