Flow patterns in friction stir welds of AA5083 and AA6082 alloys

The flow patterns in dissimilar friction stir welds of AA5083-O and AA6082-T6 alloys have been studied. It was observed that material flows (pushes but does not mix) more from the advancing side into the retreating side. Material flow from the retreating side to the advancing side only occurs in the tool shoulder domain, and the pull is greatest at the transition region between the tool shoulder domain and the tool pin domain. It was also observed that materials tend to extrude out only in the thermomechanically affected zone of the retreating side, which was influenced by rotation of both the tool shoulder and the tool pin. The finest grains were present in the regions closest to the tool edge in the retreating side. The volume fraction of recrystallized grains increases down into the deeper part of the nugget from the flow arm region. Microhardness measurements revealed that regions of lowest hardness values were the nugget and the heat affected zone of the AA6082-T6 alloy side. The welding speeds had no influence on the microhardness values per se, but affected the mixing proportions in the flow arm and in the nugget stem.     

Friction stir welding of aluminium hollow extrusion: weld formation and mechanical properties

Novel friction stir welding (FSW) technique, characterised by big concave upper and small convex lower shoulders, for aluminium hollow extrusion was studied. Assisted with the lower shoulder, root flaws due to the lack of tool penetration have been eliminated. The tensile strength increased with increasing welding speed. As the welding speed increases from 50 to 200 mm min^?1, the width of the welding nugget zone (WNZ) decreases, and the ductile fractured location occurred at WNZ instead of heat affected zone (HAZ) adjacent to thermomechanically affected zone (TMAZ). The interface between the TMAZ and HAZ exhibited the lowest microhardness. The results indicated that the novel FSW method has the potential to join tubular structures and hollow profiles widely used in transportation industries.     

Microstructure and tensile properties of friction welded aluminum alloy AA7075-T6

Solid-state welding processes like friction welding and friction stir welding are now being actively considered for welding aluminum alloy AA7075. In this work, friction welding of AA7075-T6 rods of 13 mm diameter was investigated with an aim to understand the effects of process parameters on weld microstructure and tensile properties. Welds made with various process parameter combinations (incorporating Taguchi methods) were subjected to tensile tests. Microstructural studies and hardness tests were also conducted. The results show that sound joints in AA7075-T6 can be achieved using friction welding, with a joint efficiency of 89% in as-welded condition with careful selection of process parameters. The effects of process parameters are discussed in detail based on microstructural observations.     

Effects of welding parameters and post-heat treatment on mechanical properties of friction stir welded AA2195-T8 Al-Li alloy

In this study, the effects of main welding parameters(rotation speed(ω) and welding speed(v)) on the microstructure, micro-hardness distribution and tensile properties of friction stir welded(FSW)2195-T8 Al-Li alloy were investigated. The effects of T6 post-treatments at different solution and aging conditions on the mechanical properties and microstructure characteristics of the FSW joints were also investigated. The results show that with increasing and v, both strength and elongation of the joints increase first, and then decrease with further increase of and v. All the joints under varied welding parameters show significant strength loss, and the strength reaches only 65% of the base metal. The effect of T6 post-heat treatment on the mechanical properties of the joints depends on the solution and aging conditions. Two heat treatment processes(480℃× 0.5 h quenching + 180℃× 12 h,520℃× 0.5 h quenching + 180℃× 12 h aging) are found to increase the joint strength. Furthermore,low temperature quenching(480℃) is more beneficial to the joint strength. The joint strength can reach 85% of the base metal. Whereas both low temperature aging(140℃× 56 h) and stepped aging(100℃× 12 h + 180℃× 3 h) processes decrease the joint strength. After heat treatment all the joints show decreased ductility due to the obvious grain coarsening in the nugget zone(NZ) and thermo-mechanically affected zone(TMAZ).     

Microstructure and mechanical properties of friction stir welded 7136–T76 aluminium alloy

Abstract

The microstructure of the weld was examined by light and electron microscopy (scanning and transmission). The various regions, i.e. thermomechanically affected zone, heat affected zone and unaffected base material, were studied in detail to better understand the microstructural evolution during friction stir welding and its impact on basic mechanical properties. The change in morphology of the strengthening phases reflected the relative temperature profile and the amount of deformation across the welded joint during the stir welding process. The centre of the weld was composed of fine grains and coarse particles identified mainly as MgZn₂. In the thermomechanically and heat affected zones, the grain size was not uniform, and the strengthening phases filled the grain interiors, while grain boundaries were surrounded by precipitation free zones. The size of the strengthening phase decreased towards the base material. The hardness profile of the friction stir weld displayed the lowest hardness on the retreating side. Tensile properties of the weld itself were superior to those for material containing weld.     

异种铝合金搅拌摩擦焊接接头的微观组织与力学性能

采用搅拌摩擦焊方法对4mm厚的5083铝合金与6082铝合金进行了焊接,对焊接接头的微观组织和力学性能进行了分析。结果表明,焊核区由细小的等轴再结晶组织构成,6082铝合金在前进侧的抗拉强度大于5083铝合金在前进侧的抗拉强度,正弯试验与背弯试验角度都达到180°。     

Process optimisation and mechanical properties of friction stir lap welds of 7075-T6 stringers on 2024-T3 skin

This paper focuses on the results of process optimisation and mechanical tests that were used to ascertain the feasibility of using friction stir welding (FSW) to join stringers to skin. The effects of process parameters on weld quality of 1.5-mm 7075-T6 stringers lap-joined on 2.3-mm 2024-T3 skins were investigated. Advancing and retreating side locations on the joint configuration were alternated to determine optimal design arrangements. The effects of travel and rotation speeds on weld quality and defect generation were also investigated. Weld quality was assessed by optical microscopy and bending tests. It was found that: (i) the increase of the welding speed or the decrease of the rotational speed resulted in a reduction of the hooking size and top plate thinning but did not eliminated them, (ii) double pass welds by overlapping the advancing sides improved significantly the weld quality by overriding the hooking defect, and (iii) change of the rotational direction for a counter clockwise with a left-threaded probe eliminated the top sheet thinning defect. Subsequently, FSW lap joints were produced using optimum conditions and underwent extensive mechanical testing program. Several assembly configurations including discontinuous and continuous welds as well as single and double pass welds were produced. The results obtained for cyclic fatigue performance of FSW panels are compared with riveted lap joints of identical geometry. S–N curves, bending behaviour, failure locations and defect characterisation are also discussed. It was found that: (i) the tensile strength of FSW joints approached that of the base material but with a significant reduction in the fatigue life, (ii) the probe plunge and removal locations served as the key crack nucleation sites in specimens with discontinuous welds, and (iii) double pass welds with overlapping advancing sides showed outstanding fatigue life and very good tensile properties. The present work provided some valuable insight into both the fabrication and application of FSW on stringer/skin lap joints.     

Force response characteristics and mechanical properties of friction stir welded AA2024 sheets

Process force and tensile properties in friction stir welding of AA2024 sheets were studied. Results show that the forces present a periodic variation with the same periodicity which is nearly equal to the time of one tool rotation, and thus it only depends on rotation speed. With increasing welding speed the forces increase gradually, while with increasing rotation speed the forces first decrease and then increase. Joints with superior strength-ductility synergy are produced at 900?rev?min^?1–300?mm?min^?1 and 1000?rev?min^?1–350?mm?min^?1. These joints experience nearly the same peak temperature and axial force. As heat input increases the failure initiates from the interface between nugget zone (NZ) and thermo-mechanically affected zone to heat-affected zone continuing to NZ.     

Characterisation and modelling of toughness in 6013-T6 aerospace aluminium alloy friction stir welds

The effect of the friction stir welding process on the toughness properties of AA6013-T6 sheet has been investigated. The alloy was received and welded in the peak aged T6 condition and the toughness measured at intervals across the weld by means of a notched tear test, with subsequent fractographic examination via field emission gun scanning electron microscope (FEGSEM) and microstructural characterisation via optical microscopy and energy dispersive X-ray (EDX). It is shown that the controlling factors for toughness in AA6013-T6 following FSW are the population and distribution of the coarse α-(Al,Fe,Si,Mn) intermetallic particles, with strength variations caused by precipitate dissolution, coarsening and transformation representing a secondary consideration. Minimum toughness occurs at the boundary between the weld nugget and the heat-affected zone due to the alignment and concentration of coarse particles at this point by the FSW process. A simple model is implemented and provides a reasonable prediction of the weld toughness from simple microstructural observations.     

Effect of Process Parameters on Tensile Strength of Friction Stir Welded Cast LM6 Aluminium Alloy Joints

This paper reports the effect of friction stir welding(FSW)process parameters on tensile strength of cast LM6 aluminium alloy.Joints were made by using dierent combinations of tool rotation speed,welding speed and axial force each at four levels.The quality of weld zone was investigated using macrostructure and microstructure analysis.Tensile strength of the joints were evaluated and correlated with the weld zone hardness and microstructure.The joint fabricated using a rotational speed of 900 r/min,a weldin...     

搅动摩擦焊原理及应用

搅动摩擦焊是近十年里出现的最引人注目的新型焊接方法。文中介绍了搅动摩擦焊的原理、特点、焊缝组织及应用 ,并对该焊接方法的应用前景进行了展望     

Process optimisation and microstructural evolution of friction stir spot-welded Al6061 joints

The joint strength and subsequent microstructural evolution of a friction stir spot-welded AA6061-T6 alloy was investigated according to the process parameters: tool rotation speed, dwell time and pin angle of the tool. A maximum tensile shear load of 2.78?kN was obtained from the joints generated under a combination of process variables like 1000 and 1500?rev?min^?1, 5?s, 5°. Under a fixed pin angle of 5° and a rotational speed of 1000?rev?min^?1, an increase in dwell time from 1 to 5?s resulted in a considerable increase in tensile shear load. An empirical process map under a fixed tool design is proposed to determine a feasible range of process conditions.