Microstructure Of Friction Stir Research Articles

Inhomogeneity of microstructure in friction stir welded TC17 alloy joint and its effects on mechanical behavior

Friction stir butt welding was carried out to assemble 6 mm-thick TC17 titanium alloy plates with a W–Re weld tool. Inhomogeneous microstructures were obtained in stir zone (SZ) and heat affected zone (HAZ) of the weldment. A series of tests were conducted to reveal the influence of inhomogeneity of microstructure on mechanical behavior. Comparative refined β phase without precipitating secondary metastable microstructure generated a soft SZ and favored on the ductility of weldment. Strain localization during tension was promoted by the interface of HAZ and SZ that formed by thermal-mechanical coupling effects. Coincidentally, fatal fatigue cracks were verified to nucleate around the same region, and presented in a stress dependent mode.

Influence of Tool Pin Profile on Mechanical Properties and Microstructure of Friction Stir Welded Aluminium AA7075 Alloy

The present investigation describes the effect of different tool pin profiles on microstructure and mechanical properties of friction stir welded aluminium AA-7075 alloy. The tool pin profiles namely taper cylindrical threaded (TT), cylindrical (CT), square (SQ), triangular (TR), pentagonal (PT), hexagonal (HX) with constant shoulder diameter have been selected to make joints. The friction stir welding was done at constant tool rotational speed and traverse speed. From this study, it is noted that the weld joints prepared using taper cylindrical threaded pin profile exhibited good mechanical properties when compared to other pin profiles. It is due to more surface contact of tool pin and production of equiaxed fine grain structure in the weld region.

Investigations on the Hardness Distribution and Microstructure of Friction-Stir-Welded 6082 Aluminum Alloy

The hardness and microstructure of friction stir welded (FSW) 6082 aluminum alloy joint were investigated by Vickers microhardness test, optical microscopy (OM), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). The hardness distribution is in a W shape, and from the base metal to the heat affected zone (HAZ) the hardness decreases from 103 HV to 72 HV, then gradually increases to 84 HV at the nugget zone (NZ). The grains of base metal (BM) are elongated and composed of a great quantity of low-angle grain boundaries. The nugget zon was of quite fine recrystallized grains. For the thermomechanical affected zone (TMAZ), the grain size is a little smaller than that of base metal and some low-angle grain boundaries remain. In the heat affected zone, the grain size was similar to that of the base metal. The β'' phase (Mg5Si6) and Al-Mn-Si particles are dispersed in the base metal. . In the heat affected zone, β'' phase transforms to β' phase (Mg9Si5). The hardness distribution in a W-shape was discussed on the basis of grain size, density of low-angle grain boundary and secondary phases.

Microstructure of Friction Stir Welded AlSi9Mg Cast with 5083 and 2017A Wrought Aluminum Alloys

Wrought aluminum alloys 5083 and 2017A were each joined with cast aluminum alloy AlSi9Mg through friction stir welding in butt weld configurations. For each material system, the wrought and cast alloy positions, i.e., the advancing side or the retreating side, were exchanged between welding trials. The produced weldments were free from cracks and discontinuities. For each alloy configuration, a well-defined nugget comprised of alternating bands of the welded alloys characterized the microstructure. The degree of mixing, however, strongly depended on which wrought alloy was present and on its position during processing. In all cases, the cast AlSi9Mg alloy dominated the weld center regardless of its position during welding. Electron backscattered diffraction analysis showed that the grain size in both alloys (bands) constituting the nugget was similar and that the majority of grain boundaries exhibited a high angle character (20°-60°). Regardless of the alloy, however, all grains were elongated along the direction of the material plastic flow during welding. A numerical simulation of the joining process visualized the material flow patterns and temperature distribution and helped to rationalize the microstructural observations. The hardness profiles across the weld reflected the microstructure formed during welding and correlated well with the temperature changes predicted by the numerical model. Tensile specimens consistently fractured in the cast alloy near the weld nugget.

Tensile Properties and Microstructure of Friction Stir Welded Cast Al-Mg-Sc Aluminum Alloy

The mechanical behavior of Friction Stir (FS) welds made under the most favorable choice of parameters was determined using tensile tests and was correlated to the microstructures of the FS welded cast Al-Mg-Sc alloy plate and the base metal. FS Zones in the Cast Al-Mg-Sc specimens were much harder than the cast base metal. The global joint fractured in the base metal, and thus possessed greater tensile strength than the base metal. Component part joint samples with lesser gage length failed at the weld nugget. Microstructural evaluation of the alloy plates revealed that due to FS welding, fine and fragmented dynamically recrystallized grains have been formed in the weld nugget. The fine fragmented microstructure of the weld nugget was responsible for better tensile properties than the cast base metal. These results clearly show that FS welding is an optimum/suitable welding process for cast Al-Mg-Sc alloys.

Investigation of Microstructure in Friction Stir Welded Al-Cu-Li Alloy

It is well known that the addition of Li to aluminum alloys offers an attractive combination of low density and high modulus, which are useful for lightweight structures of aerospace vehicles. However, microstructure of Al-Li alloys are complex, which consist of a number of equilibrium and metastable phases. In addition, Al-Li alloys are weldable but the weldability is not as good as that of other aerospace alloys. This is due to the reactive property of element Li during melting and causes porosity, cracking and low joint efficiency. In friction stir welding (FSW), rotating welding tool generates frictional heat and by keeping the tool rotating and moving speed, the heat from friction causes the plate to soften without melting. Therefore, this solid state welding is adequate to Al-Li alloys. The friction stir welded joint was divided into 9 regions and each microstructure was investigated in detail to present the microstructure evolution and material flows during friction stir welding process. The recrystallized structure is observed in nugget zone and the evidence of initiation of dynamic recrystallization is found around the boundary between thermo-mechanically affected zone (TMAZ) and nugget region. This paper describes the results of a study to investigate the microstructure change of Al-Cu-Li alloy during the friction stir welding process.

Tensile Properties and Microstructure of Friction Stir Welded Joints 2195-T8 Aluminum Alloy

Friction stir welding is a widely used welding process for aluminum alloys because it avoids many of the problems of conventional fusion welding. This process is beneficial especially for lithium containing aluminum alloys in which the reactive property of element Li causes porosity and hot cracking during melting and solidification. In friction stir welding process, each region undergoes different thermo-mechanical cycles and produces a non-homogeneous microstructure. In the present study, the mechanical properties and microstructure of a 2195-T8 aluminum alloy joined with friction stir welding were investigated. The change in microstructure across the welded joint was found to correspond to microhardness measurement. The microstructure was characterized by the presence of severely deformed grains and fine recrystallized grains depending on the region. Tensile tests shows the optimum condition was obtained at the tool rotating speed of 600rpm and the traveling speed range from 180 to 300mm/min.

Effects of Heat Transfer on Microhardness and Microstructure of Friction Stir Welded AA 6061 Aluminum Alloy

In this research work, the effects of heat transfer on microhardness, microstructures of friction stir welded AA 6061-T6 Aluminum alloy butt joints advancing side and retreating side are analyzed. A three dimensional finite element model is developed to study the thermal history in the butt welding of AA 6061 aluminum alloy using ANSYS package. Solid 70 elements are used to develop the model and a moving co-ordinate has been introduced to model the three-dimensional heat transfer process because it reduces the difficulty of modeling the moving tool. In this model, the main parameter considered is the heat input from the tool shoulder and tool pin. As a result, the temperature distributions of the weld at a welding speed of 1.25mm/sec were obtained.

The evolution of precipitation and microstructure in friction stir welded 2195-T8 Al–Li alloy

Precipitate and microstructure evolution in friction stir welding of 2195-T8 aluminum alloy was characterized by transmission electron microscopy. The results show that precipitations in the base metal primarily consist of T1 (Al2CuLi) platelets and small amounts of θ′ (Al2Cu) and τ2 (Al7Cu2Fe) phase. In the heat affected zone (HAZ), these precipitations dissolve during welding, allowing the re-precipitation of δ′ (Al3Li) and β′ (Al3Zr) during cooling. δ′ and β′ phase are the major strengthening phase in the weld nugget zone (WNZ), which results in the observed lower microhardness of the nugget region. Differential scanning calorimetry (DSC) curve is used to confirm and interpret the results provided by the microscopy.

Effect of Preheat Temperature on Friction Stir Welded Aluminum Alloy 5052 Joints

The effects of preheat temperature on mechanical properties and the microstructure of friction stir welded (FSW) aluminum alloy 5052 joints were studied in the present work. Heated air from Hot Gun was applied in front of the FSW tool to give the preheat on friction stir welding process. Preheat temperature was set 150°C, 250°C and 300°C. Mechanical properties were correlated and analyzed according to tensile strength, macro and microstructure. Defect free weldswere obtained at all preheat variations. The increasing preheat temperature produced the coarser grain size, it influencedthe little decrease both the tensile strength and hardness of joints.

Microstructure of friction stir welded joints of 2017A aluminium alloy sheets

The present study examines a friction stir welded 2017A aluminium alloy. Transmission electron microscope investigations of the weld nugget revealed the average grain size of 5 microm, moderate density of dislocations as well as the presence of nanometric precipitates located mostly in grains interiors. Scanning electron microscope observations of fractures showed the presence of ductile fracture in the region of the weld nugget with brittle precipitates in the lower part. The microhardness analysis performed on the cross-section of the joints showed fairly small changes; however, after the artificial ageing process an increase in hardness was observed. The change of the joint hardness subject to the ageing process indicates partial supersaturation in the material during friction stir welding and higher precipitation hardening of the joint.

Study of PM2000 microstructure evolution following FSW process

The materials reinforced by oxides dispersion, usually called ODS (Oxide Strengthened Dispersion), have a vast applicability because of their excellent mechanical resistance at medium and high temperatures. Their weldability is one of the technological issue which remain today. The Friction Stir Welding process is a means of welding which would make it possible to preserve the oxides dispersion in the metal matrix. As a solid-state joint process, Friction Stir Welding (FSW) joins metals by locally introducing frictional heat and plastic flow by rotation of the welding tool with resulting local microstructure changes. The local microstructure determines the weld mechanical properties. Therefore, it is important to investigate the relationship between the microstructure and the mechanical properties. In this work, the PM2000 steel microstructure in friction stir (FS) weld was studied by neutron scattering. The oxides size distribution evolution between the bulk and the weld was analyzed by SANS. Crystallographic texture variations during friction stir processing were investigated by neutron diffraction. Indeed, heating and severe plastic deformation can significantly alter the original texture and then affect the physical and mechanical properties. The texture was studied in different zones: in the bulk, in the thermo-mechanically affected zone (TMAZ) and is the heat-affected zone (HAZ) of the PM2000 alloy. Lastly, the stresses distribution after welding is a crucial parameter for the mechanical properties. Their variation prediction under FSW, taking into account of the microstructure evolution which occur during the process, is very delicate. The neutron diffraction allowed characterizing the distribution of the stresses in the different zones.

Crystallography of transformed β microstructure in friction stir welded Ti–6Al–4V alloy

The electron backscattering diffraction technique was employed to study the crystallography of the transformed β microstructure developed in a friction stir welded Ti–6Al–4V alloy. Direct orientation measurements in the α and β phases together with analysis of the misorientation distribution in the α phase showed that β-to-α phase transformation was governed by Burgers orientation relationship.

Superplastic Properties and Microstructure of Friction Stir Welded Joints of Zn-22wt.%Al Alloy

Deformation mechanism of room-temperature superplasticity in Zn-22wt%Al alloy was investigated by the direct observation during deformation. It was revealed that the dominant deformation mechanism of room-temperature superplasticity was grain boundary sliding. Also, superplastic properties and microstructure of friction stir welded Zn-22wt.%Al alloy were investigated, where Friction Stir Welding (FSW) has received a great deal of attention as a new solid-state welding technique. A sound jointing material was obtained successfully, and extremely fine and equiaxed grains were created in the stir zone. In addition, it was indicated that superplastic forming of the FSWed Zn-22wt.%Al alloy could be feasible. However, the tensile strength and elongation of the joint at room temperature were lower than that of the base material.

Relation between Strength and Microstructure in Friction Stir Welded Joints of A383 and A5052 Aluminum Alloys

Friction stir welding (FSW) was applied to joints of ASTM-A383 (Al- 11 %Si- 3%Cu-0.3Mg alloy) die casting and 5052 (Al- 2.5%Mg alloy) rolled sheets. A tensile specimen of FSWed A383 and 5052-0 alloys was broken in the base metal part of the latter alloy. Its tensile strength was about 195MPa, which was equal to that of 5052-0. On the other hand, a tensile specimen of FSWed A383 and 5052-H34 alloys was broken in heat affected zone (HAZ) or thermo-mechanical affected zone (TMAZ) of FSWed 5052 side. The joint showed the tensile strength of 220MPa, which was somewhat lower than the latter alloy strength, 245MPa. Vickers hardness test result showed that tensile specimens were broken at a portion of the lowest strength in the joint.

Microscopic Observations of Friction Stir Welded 6061 Aluminum Alloy

As the automotive industry trends towards increased use of aluminum, the friction stir welding process offers many potential benefits for joining of aluminum. In this study, the microstructure in friction stir welded 6061 aluminum alloy was observed by metallographic technique, electron backscatter diffraction pattern (EBSD) and optical microscopy. The microstructure in the heat affected zone (HAZ) was significantly different from that in a thermo-mechanically affected zone (TMAZ). EBSD indicated that many more low-angle grain boundaries in TMAZ, i.e., subgrains with a recovered granular structure, were observed than in HAZ. Friction heating and plastic flow during friction stir welding created fine recrystallized grains and recovered grains in the TMAZ. The friction stir welding process produced a softened region in the 6061 Al welded alloy. In the stir zone, equiaxed grains were created and the grain size was smallest in the bottom area.

Relationship between mechanical properties and microstructure in friction stir welded Al alloys

Relationship between mechanical properties and microstructure in friction stir welded Al alloys

Relationship between mechanical properties and microstructure in friction stir welded Al alloys

Relationship between mechanical properties and microstructure in friction stir welded Al alloys

Ａｌ合金ＦＳＷ部の機械的特性とミクロ組織

Ａｌ合金ＦＳＷ部の機械的特性とミクロ組織

Microstructure of Friction Stir Welded Joints in AA5182

Two 2.5 mm thick hot mill stock sheets of AA5182 aluminum alloy were pretreated differently before friction stir welding, one was cold rolled by 20% reduction in thickness whereas the other was 20% cold rolled then recovery annealed at 230 °C for 100 hours. After friction stir welding of these two sheets, a uniform dynamic recrystallized microstructure of fine grain size with no evidence of abnormal grain growth in the heat affected zone of the weld was obtained. X-ray pole figure study showed that the weld zone comprised of triclinic texture components which were recognizably of rotated cube texture and could be quantitatively analyzed. The predicted sheet formability of the weld zone is better than that of the start material.