Friction welding of AA6061 to AISI 4340 using silver interlayer SURESH D. MESHRAM＊, G. MADHUSUDHAN REDDY

Challenges, process requisites/inputs, mechanics and weld performance of dissimilar micro-friction stir welding (dissimilar μFSW): A comprehensive review

Structural integrity and high specific stiffness made wide applicability of aluminum alloys for various transport vessels in the automobile and aerospace industries. The advent of friction stir welding (FSW) is making it more realizable with the advantage of welding of dissimilar materials in solid-state. However, the lack of online defect monitoring techniques in FSW bars the wide use of it in industries. Therefore, the online assessment technique in FSW is a focal research area because of its propensity to reduce material wastage, rework time, and cost. This article reviews recent research efforts on online defect monitoring in FSW of aluminum alloys, intending to identify research gaps that need to be addressed to boost the effectiveness of the online welding process. In this study, the sensor-based monitoring approach in literature was grouped into two: a single sensor approach and the multisensory approach. It was noticed that although researchers using the single sensor detection approach recorded higher prediction accuracy, the use of multiple sensors has been demonstrated to give hope towards the development of robust detection of defects that will be able to cope with variations in material thickness and type of materials. This study further suggests the need for research efforts to focus on grey-box online monitoring techniques, sensor fusion, and cloud computing as pathways towards industrial adoption of online defect monitoring.

A Critical Review on the Trends Toward Effective Online Monitoring of Defects in Friction Stir Welding of Aluminum Alloys

https://www.jstage.jst.go.jp/article/qjjws1943/38/9/38_9_970/_pdf

Welding of Copper and Copper Alloys

The butt joint of an Al alloy ultrathin plate with a thickness of 0.5 mm is realized by a high rotational-speed friction-stir welding process. It overcomes the welding difficulty that the ultrathin plate is often torn, and it cannot be formed by conventional friction-stir welding. The results show that the weld surface is well-formed at a high-rotational speed (more than 8000 rpm), and there are no obvious defects in each area of the joint section. The nugget zone (NZ) is a recovery recrystallization structure dominated by large-angle grain boundaries, with a grain size of about 4.9 μm. During grain growth, the texture is randomly and uniformly distributed, and the strength is balanced. The microhardness of the NZ increases significantly with the increase in rotational speed, and the fluctuation range of hardness value is small. The NZ β–Mg2Si is finer and significantly less than the base metal (BM). The heat dissipation of the thin plate is fast, so a Cu plate is used as the backing plate to slow down the steep temperature-drop process in the weld area. Compared with a low rotational speed, the precipitation amount of brittle phase Al–Cu–Mg–Cr and Al–Fe–Si–Mn is significantly reduced, which is conducive to improving the mechanical properties of the joint. At a high rotational speed, 12,000 rpm, the best tensile strength of the joint is 220 MPa, which is about 76% of the BM (290 MPa), and the highest elongation is 9.3%, which is about 77.5% of the BM (12%). The fracture mode of the joint is a typical plastic fracture.

Effect of High Rotational-Speed Friction-Stir Welding on Microstructure and Properties of Welded Joints of 6061-T6 Al Alloy Ultrathin Plate.

In the friction stir welding (FSW) of ultra-thin dissimilar metal sheets, different physical material properties, the reduction of plastic metal in the weld zone, and insufficient plastic metal flow lead to poor weld seam shapes and joint qualities. Therefore, it is necessary to study the flow behavior during the FSW of ultrathin sheets. In this study, micro friction stir welding (μFSW) was conducted and analyzed for the butt welding of 0.6-mm-thick ultrathin brass (H62-H) and pure copper (T2-Y) sheets. By analyzing the electric signals of the temperature and force during the welding process, testing the mechanical properties, and analyzing the metallography of the joint, the influences of the process parameters on the metal flow behavior during μFSW were studied. In the proper process conditions, the material preferentially migrated and concentric vortex flow occurred in the vicinity of the shoulder and tool pin action areas. The copper was pushed from the retreating side (RS) to the advancing side (AS) of the weld, allowing it to flow more fully. A mixture of both materials formed at the bottom of the weld nugget, and less migration occurred in the heat-affected zone of the AS at this time. The highest tensile strength can reach 194 MPa, accounting for 82.6% of the copper. The presence of brittle phases Cu5Zn8, AgZn3 and AgZn caused the hardness to fluctuate slightly.

Shi Wenchen

Papers

The Preliminary Exploration of Micro-Friction Stir Welding Process and Material Flow of Copper and Brass Ultra-Thin Sheets.

Study of the mechanical properties and microstructures of conical joints for aluminum/steel continuous drive friction welding