Microstructure and morphology evolution of probeless friction stir spot welded joints of aluminum alloy

Chen

Pan

et al. 2019

Metals

By controlling various friction stir spot-welded (FSSW) factors, two base sheets AA 5052-H32 and 6061-T6 were selected to bond similar and dissimilar metal joints while considering dissimilar configuration orders. The effects of weld parameters on the sheer strength and peel strength were separately developed into empirical models utilizing the integrated central composite matrix design and response surface methodology (RSM). Meanwhile, the finite element (FE) analysis of the multi-axis load-bearing characteristics for automotive solder joints during service was carried out. As a result, the weights of the shear and axial stress, accounting for 90.5% and 9.5% respectively, were employed to restrict the relationship between multiple target properties, and the resulting security strength was applied to determine the feasible domain in subsequent parametric optimization. In order to enable the optimal multi-axis capacities in accordance with the load mode, the genetic algorithm NSGA-II was chosen to compute the Pareto front and further determine the best compromise solutions. The obtained optimums corresponding to each joining condition were validated by confirmation runs, indicating that this coupled multi-objective optimization approach based on working conditions was beneficial to the targeted improvement of post-weld mechanical properties.

Section: Effects Of Process Parameters On Responsesmentioning

confidence: 99%

Multi-Objective Optimization of Friction Stir Spot-Welded Parameters on Aluminum Alloy Sheets Based on Automotive Joint Loads

Chen

Pan

et al. 2019

Metals

“…Although such methods as fusion welding and brazing can realize the joining of aluminum and steel [14], internal stress, cracks, and pores in joints often lead to poor joint quality and mechanical properties [15,16].…”

Section: Introductionmentioning

confidence: 99%

Microstructure and mechanical properties of 6061-T6 aluminum alloy and Q235 steel via probeless friction stir extrusion joining

Zhao

et al. 2021

Preprint

Aluminum alloy and steel composite structures are increasingly and widely used in the automotive industry and other fields owing to their advantages of light weight and high comprehensive performance. The high-quality joining of aluminum alloy and steel has become the research focus in China and overseas. The current study proposes a probeless friction stir extrusion joining (P-FSEJ) process to avoid intermetallic compounds, reduce wear of tools, and obtain a spot joint without keyhole defects. Strong mechanical interlock is formed after that the plasticized aluminum alloy (AA) 6061-T6 is extruded into the prefabricated threaded hole of a Q235 steel plate in the P-FSEJ process. Three distinct zones in the typical symmetrical “basin-shaped” P-FSEJed joint are observed. In addition to the rotation speed, the diameter of the threaded hole is also specifically used to study the influence on the mechanical properties of the joint. When the rotation speed is 1200 rpm, the maximum tensile-shear loads of the M6 and M7 threaded hole joints are 2882.93 N and 3344.74 N, respectively, while the M8 threaded hole joint is 4139.58 N at rotation speed of 1000 rpm. Two typical fracture failure modes of the P-FSEJed joints, namely, rivet shear and rivet pullout-shear fractures, are obtained under tensile-shear loading. Lastly, the P-FSEJed joints with mode “P” fracture failure generally have high strength and energy absorption capability.

“…A tool shape has been investigated to avoid tool wear and deterioration of joint strength caused by a “hook” unbonded interface and keyhole. Recent research on FSSW of an Al alloy revealed that a pinless tool can form a good joint without the hook interface and keyholes [ 13 , 14 , 15 ]. Mousavizade et al applied pinless FSSW on a mild steel sheet with a projection-backing anvil and proved that the technique provided high tensile strength because of the absence of keyholes [ 16 ].…”

Section: Introductionmentioning

confidence: 99%

Transient Microstructure Evolutions and Local Properties of Dual-Phase 980 MPa Grade Steel Via Friction Stir Spot Processing

Taniguchi¹,

Lim

Flores‐Betancourt

et al. 2020

Materials

Friction stir processing is a novel solid-state process to modify microstructures and their properties by intense, localized plastic deformation. However, little research has been reported for microstructure evolutions of advanced high-strength steels during the process. The present work focuses on the study of transient microstructure changes and local mechanical properties for friction stir spot processed dual-phase (DP) 980 MPa grade steel (DP980) under different peak temperatures. A pinless silicon nitride ceramic tool was used to produce relatively simple material deformation and flow near the tool. Friction stir spot processed steel samples were characterized by optical and electron microscopies. Furthermore, Vickers microhardness and nano-indentation measurements were used to study local mechanical properties for correlation with microstructures. A swallow layer of refined grains (<0.6 µm) was obtained with a low peak temperature (under 400 °C), whereas higher peak temperatures (>Ac1) led to a change in grain size with different microstructures (fine-grained DP or martensite). Electron back-scattered diffraction characterizations revealed a large deformation in the as-received microstructures (mixture of ferrite and tempered martensite) induced by friction stir spot processing, leading to recrystallization and grain refinement around the stirred zone. Also, nano-indentation measurements showed a higher hardness than the hardness of the as-received DP980. Friction stir processing with different process conditions effectively changed microstructures and local mechanical properties.