Friction Stir Lap Research Articles

Study on Friction Stir Lap Welding of Aluminium to Steel Sheets

Friction stir lap welding (FSLW) of 6061-T6 aluminium sheet and DX51D galvanized steel sheet was carried out by adding zinc foil to the lap interface and studying the influence of the zinc foil on the formation mechanisms and mechanical properties. The influence of the thickness of zinc foil, the plunge depth of the shoulder and the shape of the tools on the mechanical properties of the weld are discussed. Zinc foil reduced the generation of brittle intermetallic compounds, such as Fe4Al13. During the welding process, the axial force was small due to the high rotating speed. Liquid zinc was retained at the interface, where eutectic Al–Zn with low melting point and an Fe–Zn compound were generated to achieve the metallurgical combination of aluminium and steel. The fracture was located in the heat affected zone (HAZ) of the 6061-T6 base aluminium. The results showed that when the zinc foil was too thin, there was less zinc content at the interface; the resulting Al–Zn eutectic had low melting point, was not fully spread and had poor continuity, resulting in poor mechanical properties. When the zinc foil was too thick, a large amount of zinc-based solid solution was generated at the interface, and most of the fracture occurred in the zinc-rich layer.

Enhancement of joint strength in friction stir lap welding between AA6061 and AISI 304 by adding diffusive coating agents

This study focuses on the usage of fly-ash and Al-12%Si as diffusive coating materials over AISI 304 steel welded with AA 6061 in friction stir welding process to improve the joint quality. Various mechanical and metallurgical studies have been carried out to evaluate the characteristics of the weld, and investigate and compare the effect of the two coating materials. Formation of intermetallic reaction layer has been found to be an influential parameter affecting the joint quality. Aluminium-rich intermetallic reaction layer has been observed in the bare welds, whereas the coated samples have been found to have ferrous-rich intermetallic reaction layer.

Interfacial microstructures and mechanical properties of dissimilar titanium alloy and steel friction stir butt-welds

Dissimilar welding of titanium to steel has received significant attention because of its potential application in power generation and chemical industries. However, it is considered to be very challenging to use fusion-welding processes to join Ti to steel due to their dramatically different thermo-physical properties and chemical compositions. In this work, linear friction stir butt-welding was successfully used to join 2 mm thick sheets of titanium alloy, Ti6Al4 V to medium carbon steel, 30CrMnSiNi2A. Defect-free butt-welded joints were produced using travel speeds from 47.5–75 mm/min with a constant tool rotation speed of 750 RPM. With increasing travel speed, the thickness of the interfacial reaction layer gradually decreases. FeTi intermetallic compound was detected at the interface by micro-XRD testing. An optimal interfacial reaction layer approximately 1 μm thick was formed in the weld made at a travel speed of 75 mm/min. A reaction layer ranging from ∼5 to 60 μm thick was found at the interface with a travel speed of 47.5 mm/min. Such thick reaction layer is in contrast with the thinner layer formed in friction stir lap welds, which is believed to be related to the relatively higher welding temperature of friction stir butt welds. Welds formed at travel speeds ranging from 47.5–75 mm/min exhibit higher tensile strengths than the steel base material and were found to fracture from thermo-mechanically affected zone to heat affected zone on steel side or at the interfacial reaction layer on Ti-side.

Dissimilar Al/Mg alloys friction stir lap welding with Zn foil assisted by ultrasonic

The Zn-added ultrasonic assisted friction stir lap welding (UaFSLW) was carried out to improve the quality of dissimilar Al/Mg alloys joint. The effects of ultrasonic power on the joint quality were also investigated. The results indicated that the larger effective lap width and mixing region between Mg and Al (Mg/Al MR) were attained by Zn foil addition and external ultrasonic assistance. Compared with the conventional joint, the finer and better-distributed Mg-Zn IMCs placing the continuous Al-Mg IMCs were formed in the Mg/Al MR of the Zn-added UaFSLW joint. The Zn foil addition and external ultrasonic assistance significantly improved the tensile shear load of the joint, and the load was increased with the increase of the ultrasonic power. The maximum tensile shear load of 7.95 kN was attained, which was 52.6% larger than that of the conventional joint.

Microstructure and mechanical properties of friction stir lap AA6061-Ti6Al4V welds

The AA6061 and Ti6Al4V plates were joined by atomic diffusion and interfacial reactions. Layers of solid solution and intermetallic compound were both formed at the interface, and the interface thickness increased as the heat input increased. The intermetallic compound layer was found to be mainly composed of TiAl3. The shear strength of the friction stir lap AA6061-Ti6Al4V welds was found determined by the interfacial microstructure. The shear performance was promoted initially with the increase of interface thickness due to the formation of intermetallic compound. The maximum shear load of 4500 N was reached with a 7.5-μm-thick interface. When the thickness of interface further increased, the maximum shear load was found to decrease again because of the exorbitant residual stresses induced by the excessive intermetallic compounds. The fracture of the joints started with the micro-cracks formed at the intermetallic compounds and then leads to break during tensile shear test.

Effect of a Ni interlayer on microstructure and mechanical properties of WC-12Co cermet / SC45 steel friction stir welds

WC-12Co cermet was friction stir lap welded with SC45 steel with or without different thicknesses of a Ni interlayer. The visualization of the material flow was rendered easy by the insertion of the Ni layer. Welding gives rise to the formation of Widmanstätten ferrite, low temperature pearlite, bainite, martensite and retained austenite in the nuggets of the joints. Some interdiffusion is noticed at the steel-cermet, steel-Ni and Ni-cermet interfaces, which leads, in particular, to the formation of oversaturated Co solid solutions in Fe or in Ni. The increase in the Ni interlayer thickness is shown to lead to a more pronounced wear of the Si3N4 tool and to a greater amount of retained austenite in the nugget. The mechanical tests finally suggest that the interface of the Ni bearing joints is of better quality than that of the Ni-free joint.

Performance of Plunge Depth Control Methods During Friction Stir Welding

Friction stir welding is a preferred solid state welding process for Al/Fe joints, and in friction stir lap welding, the plunge depth is the most critical parameter for joint strength. We compared three plunge depth control methods, namely conventional position control, offset position control, and deflection compensation control in the friction stir lap welding of 3 mm-thick Al 5083-O alloy over 1.2 mm-thick DP 590 steel. The desired plunge depth was 0.2 mm into the steel sheet. However, the pin did not reach the steel surface under conventional position control due to deflection of the vertical axis of the welding system. In offset position control, an additional offset of 0.35 mm could achieve the desired plunge depth with considerable accuracy. Nevertheless, a gradual increase of the plunge depth along the longitudinal direction was unavoidable, due to an in-situ decrease of the material yield strengths. In deflection compensation control, the deflection is estimated by the coaxially measured plunging force and the force-deflection relationship, and then corrected by feedback control. Thus, the plunge depth is stabilized along the longitudinal direction and is precisely controlled with a 3.3-μm standard deviation of error during the tool traverse phase. There is also a consistent bias of 32 μm caused by the resolution of the measuring system, and it can be easily calibrated in the feedback control system.

Improving hook characterization of friction stir lap welded Al alloy joint using a two-section stepped friction pin

Four millimeter-thick 7N01P Al alloy sheets were welded by friction stir lap welding (FSLW) with different tools at various welding heat inputs. Results showed that the highest load could be performed by the optimization of welding parameters using a traditional tool; but, the welding parameters had an obvious effect on the joint loads and fracture modes. The tools with the stepped sections, which could control stable material flow behavior at various welding parameters during FSLW, were introduced. The platform geometry of the stepped friction pin contained two types: one had a convex platform between two sections, and the other had a concave platform between two sections. The joints obtained by the tools with the stepped sections could have a stable load at different welding parameters. Especially, in comparison with the tool with a convex platform, the concave platform acted like a concave shoulder for second stepped pin, improving the material flow during the FSLW and realizing a sound joint with a relatively flat interface morphology, which insured the stability of the joint properties (from 5.2 kN to 5.9 kN) and fracture mode (shear mode) at various welding parameters.

Improving mechanical properties of composite/metal friction stir lap welding joints via a taper-screwed pin with triple facets

Material flow rates at the horizontal and vertical directions were markedly increased by a taper-screwed pin with triple facets. A stationary shoulder could prevent plasticized materials overflowing out of the weld and make them backflow into the nugget zone, achieving good surface integrity. The short carbon fiber-reinforced poly-ether-ether-ketone and the AA2060-T8 were tightly joined, and the carbon fibers were dispersedly distributed at the nugget zone, which attributed to the effective load transfer effects and then improved the joint strength. The tensile shear strength reached 18 MPa. The combination of the stationary shoulder tool system and plunging the taper-screwed pin with triple facets into the composite was feasible and effective to improving mechanical properties of composite/metal friction stir lap welding joints.

Research on Microstructure and Mechanical Properties of Friction Stir Lap Welded Aluminum/Brass Dissimilar Joint

Research on Microstructure and Mechanical Properties of Friction Stir Lap Welded Aluminum/Brass Dissimilar Joint

Microstructure and fracture behavior of friction stir lap welding of dissimilar AA 6060-T5/ Pure copper

Microstructure and fracture behavior of friction stir lap welding of dissimilar AA 6060-T5/ Pure copper

Feasibility and interface migration characteristics of friction stir lap welding of LA141 Mg-Li alloy

Abstract2 mm-thick LA141 plates were successfully friction stir lap welded (FSLW). The similar FSLWLA141Mg-Li alloy joint appeared a downward hook on the advanced side and an upward cold lap on the retreating side. The load of lap-shear tensile testing reached 2.8 kN, and the joints failed in the interface defects. The interface migration of LA141/LA141 lap joint during FSLW process was driven by forces at interface, such as a frictional force paralleled to the thread, a downward pressure perpendicular to the surface of the thread, the resistance from unsoftened metal and its own gravity. Moreover, the FSLWof AZ31/LA141 and LA141/AZ31 furtherly verified that forces at the interface were critical factors in determining the interface migration during FSLW process.

A Study of Diffusion Phenomenon in Friction Stir Lap Welding Joints for Low Carbon Steel C10 to Aluminum Alloy AA1100-H112

In this study the friction stir lap welding was carried out by a new technique (diffusion bonding phenomenon) between (AA1100 and low carbon steel C10 sheets of 3mm and 1mm thickness respectively. These alloys have difference ranges in melting temperature and other physical properties. Different parameters were used: tool rotation speeds (630, 1250) rpm, travel speeds (80, 32) mm/min. and pin length (2.8,3) mm using cylindrical threaded pin. Many tests and inspections were performed such as tensile shear test and X-Ray diffraction tests. Microhardness and microstructure observations were conducted by using optical and SEM. The above tests were used to evaluate the weld quality and joint efficiency under different welding parameters. Best result for FSLW by diffusion phenomenon appear in (low carbon steelC10 / AA1100-H112) joint at 1250rpm in 32 mm/min. with 2.8mm pin length and the maximum tensile shear strength was (3.9)KN.It was found that the highest micro hardness was (138HV) at the interface between the low carbon steel and AA1100.

Friction stir lap welding of aluminum alloy to advanced high strength steel using a cold-spray deposition as an interlayer

To overcome the undesirable wear of pin-tip during friction stir lap welding (FSLW) of AA6022 aluminum alloy and Usibor® 1500 advanced high strength steel, a precoated Al cold-spray deposition (200 μm in thickness) has been used as the interlayer. The optimized weld shows a simple sandwich-like structure that consists of an aluminum weld, an interface, and a heat affected steel region. No intermetallic compound was found while an Al/Fe diffusion layer with an average thickness of about 10 nm was observed at the deposition/steel interface. No distinct phase transition and mechanical properties change were found in the heat affected steel region.

Influence of Rotation Speed on Microstructure and Mechanical Properties of Friction Stir Lap Welded Joints of AA 6061 and Ti6Al4V Alloys

Three-mm-thick AA 6061 plate and 2-mm-thick Ti6Al4V plate were friction stir lap welded using a W-Re pin tool. Defect-free joints were obtained at various rotation speeds ranging from 800 to 1400 rpm with a constant welding speed of 100 mm/min. The influence of rotation speed on the microstructure and mechanical properties of the Al/Ti friction stir lap welding (FSLW) joints was investigated. At low rotation speed within 1000 rpm, the obtained joint has no obvious mechanical Al/Ti intermixing at the interface. However, a significant mechanical mixture of Al and Ti alloys accompanied by hooks could be found in the joint welded at a rotation speed over 1000 rpm. Only diffusion layer was observed in the joint obtained at low rotation speed. Further, IMCs could be found in the Al/Ti mixture and hook when the rotation speed increased to 1400 rpm. The highest microhardness was measured at the interface due to the formation of IMCs. The tensile shear load of the welded joints reached the maximum at 1000 rpm and the specimens failed along the interface during the test.

Friction stir lap welding of Al to Mg assisted by ultrasound and a Zn interlayer

The friction stir lap welding (FSLW) joints of Al/Mg dissimilar alloys presented better formation and higher tensile shear strength when the Mg alloy was selected as the upper plate. Compared with Zn-added FSLW, the Zn-added FSLW assisted by ultrasound further enlarged the effective lap width, improved the mechanical interlocking and attained the finer disperse Mg-Zn intermetallic compounds in the stir zone. The maximum tensile shear strength of the joint assisted by ultrasound and a Zn interlayer reached 268 N/mm. This hybrid process with the ultrasound and the Zn interlayer provides a new method to obtain a high-quality Al/Mg dissimilar welding joint.

Effect of Revolutionary Pitch on Interface Microstructure and Mechanical Behavior of Friction Stir Lap Welds of AA6082-T6 to Galvanized DP800

Friction stir lap welding of 1.5-mm thick 6082-T6 aluminum alloy to 2-mm thick galvanized DP800 steel (Zn-coated) was carried out. Optimal welding conditions were obtained aiming to defect-free joints with good mechanical properties. The interfacial intermetallic compounds (IMCs) at the stir zone and hook zone were characterized under different revolutionary pitches. With a revolutionary pitch of 1.0 mm/rev, maximum joint strength reached 71% of that of the aluminum alloy. In the meantime, the average thickness of IMC layer is less than 1 μm; Al3.2Fe in the Al-rich side and Al5Fe2 in the Fe-rich side at the interfaces of stir zone while Al6Fe and nanocrystalline close to Al3.2Fe at the interface of the hook zone. At a relatively lower revolutionary pitch (0.5 mm/rev), Zn was found with the aggregation of Si and Mn at the hook-zone interface, leading to the generation of Al-Fe-Si phase thus decreasing the thickness of the IMC layer. In the stir zone, the revolutionary pitch has a significant influence on the interfacial microstructures. The interfacial IMC layer at 1.0 mm/rev is simple and flat, but the one at 0.5 mm/rev becomes thicker and more complex. Stir zone aluminum under different revolutionary pitches is similar in microhardness and tensile behavior. The mechanical response of joints was modeled based on linear mixture law with an iso-strain assumption and neglection of the IMC layer. The modeling results are in good agreement with the experimental ones indicating the resultant interfaces act as good as the good boundaries between dissimilar Al/steel joints.

Achieving High-Quality Al/Steel Joint with Ultrastrong Interface

An enlarged pin head with circumferential notches for friction stir lap welding was proposed to achieve Al/steel joint with ultrastrong interface. The hook defect was eliminated. The effective interfacial width of 7.5 mm was achieved. The local silicon enrichment suppressed the growth of intermetallic compounds, which was attributed to the formation of an ultrathin interfacial layer containing a Fe4Al13 layer, a single Fe2Al5 layer, a bright Fe-rich layer, and a chaotic layer. The maximum tensile shear strength reached up to 442 N/mm.

Towards attaining dissimilar lap joint of CuCrZr alloy and 316L stainless steel using friction stir welding

ABSTRACTCuCrZr alloy (Cu-0.8wt-%Cr-0.1wt-%Zr) and 316L stainless steel (Fe-0.03wt-%C-16wt-%Cr-10wt-%Ni) plates were successfully friction stir lap welded resulting in significant mechanical mixing of the two matrix elements, Cu and Fe, in the stir zone. The severe mixing not only led to improved load bearing response but also leads to form Cu-rich and Fe-rich regions in the weld nugget. The formation of these phases governs the failure mechanism of the joint. Tensile properties of the weld showed promising response when compared with joints made for the similar alloy pair by other welding techniques. This suggests strong feasibility of applying FSW for joining Cu and steel for nuclear applications.

Process and joint quality of ultrasonic vibration enhanced friction stir lap welding

ABSTRACTIn order to improve the process effectiveness and joint quality, ultrasonic vibrations were integrated with friction stir lap welding. Effect of ultrasonic exertion on the process and joint quality of AA 6061-T6 were investigated. Upon ultrasonic exertion, joints owned larger effective lap width, shorter hooks and improved strength. Weld fracture mode changed from a ductile–brittle mixed mode to a more ductile mode while the fracture path shifted from lap interface to beyond the stir zone. Material flow and interface defects were characterised using lap welded dissimilar aluminium alloy joints. Ultrasonic vibration improved the material flow and reduced the interfacial defects. Variations in failure load of joints were found in accordance with the variations in material flow and interfacial defects.