Al Side Research Articles

Microstructure and mechanical properties of ultrasonic spot welded Al/Ti alloy joints

Abstract The microstructure, hardness, and tensile properties of solid-state ultrasonic spot welded (USWed) dissimilar joints between Al5754–O and Ti–6Al–4V alloys with or without a pure Al interlayer were studied. Significant difference in the microstructure was observed at the interface of the USWed Al/Ti alloy joints, where the phenomenon of adhesion on each side of the joint with Al interlayer was more obvious than that of the joint without Al interlayer. An asymmetrical hardness profile across the dissimilar joint was observed such that the hardness value increased gradually from the Al side to the Ti side. With increasing energy input, the lap shear strength of the USWed Al/Ti alloy joint with a 75 μm thick Al interlayer first increased and then decreased, with the maximum lap shear strength reaching about 206 MPa at a welding energy of 1000 J. No samples failed at the interface when the energy was above 1000 J or the thickness of Al interlayer was more than 75 μm. The fracture was predominantly characterized by the dimple-like ductile fracture.

Friction Stir Welding of Al-Cu Bilayer Sheet by Tapered Threaded Pin: Microstructure, Material Flow, and Fracture Behavior

The fracture behavior and intermetallic formation are investigated after friction stir welding of Al-Cu bilayer sheets performed by tapered threaded pin. To do so, temperature, axial load, and torque measurements during welding, and also SEM and XRD analyses and tensile tests on the welds are carried out. These observations show that during welding from Cu side, higher axial load and temperature lead to formation of different kinds of Al-Cu intermetallics such as Al2Cu, AlCu, and Al4Cu9. Also, existence of Al(Cu)-Al2Cu eutectic structures, demonstrates liquation during welding. The presence of these intermetallics leads to highly brittle fracture and low strength of the joints. In samples welded from Al side, lower axial load and temperature are developed during welding and no intermetallic compound is observed which results in higher strength and ductility of the joints in comparison with those welded from Cu side.

Microstructure characterization and tensile properties of Mg/Al dissimilar joints manufactured by thermo-compensated resistance spot welding with Zn interlayer

Abstract Thermo-compensated resistance spot welding (RSW) with a Zn interlayer was designed to join AA5052-H12 (Al) aluminum alloy to AZ31B (Mg) magnesium alloy. A stainless steel tape placed between the upper electrode and the Al sheet acts as a heat barrier to prevent heat loss from the spot nugget on the Al side. During welding, more Al was melted to increase the percentage of Al in the liquid nugget. In the resultant Mg/Zn/Al joints produced by thermo-compensated RSW, the formation of Mg–Al brittle intermetallic compounds is restricted. The tensile–shear properties of the weld joint were improved significantly. The failure load of the Mg/Al joints was up to 2199 N, compared with the 833 N and 727 N that is produced by traditional Mg/Al RSW and Mg/Al RSW with Zn interlayer, respectively.

Thermal Stress and Fracture of Friction-Welded Joint Between Pure Ni and Pure Al with Post-weld Heat Treatment

This paper described the thermal stress and fracture of friction-welded joint between pure nickel (Ni) and pure aluminum (Al) with post-weld heat treatment (PWHT). FEM model of the joint with the NiAl interlayer at the weld interface, of which was generated as the intermediate layer consisting of intermetallic compound, was constructed. Then, FEM thermal elastic–plastic analysis was carried out, and the fracture factor of the joint during the cooling process after PWHT was described from the calculation and experimental results. The calculated thermal stresses at the adjacent region of the weld interface for the joint, due to the difference of material properties between both base metals, occurred at the early stage during the cooling process. However, the thermal stress was relatively low and had a little effect on the joint fracture. All thermal stresses of the joint with the NiAl interlayer width of 200 μm were smaller than those of 20 μm. Actually, the joint fractured between NiAl interlayer and Al side, of which was like as disbonding in the experiment. Hence, one of the main reasons for the fracture of the joint was able to be thought that the bonding strength between NiAl interlayer and Al side decreased with increasing NiAl layer width, because the thermal stress was low. Therefore, the fracture portion will be changed according to combinations of both base metals to be joined for dissimilar friction-welded joints.

Direct keyhole laser welding of aluminum alloy AA5754 to titanium alloy Ti6Al4V

The tensile strength of direct AA5754/Ti6Al4V joints performed by high speed Yb:YAG laser welding is found to be determined by morphology and phase content of dissimilar interface formed between contacting Al-rich and Ti-rich melted zones. Three types of contact interfaces were observed: (1) thin (<20μm thick) interface composed mostly by TiAl and formed under 0.2mm beam shift to Al side and linear energy of welding ≥37.5kJ/m; (2) cracked interface (190–300μm thick) composed by Al3Ti and other Al–Ti intermetallics and formed under beam shift at 0.2mm to Ti side and linear energy ≥37.5kJ/m; (3) malaxated interface composed of layers and isles of Ti3Al and TiAl forming in other tested conditions and favored by welding speed >10m/min.Maximal linear tensile force (220N/mm for 2mm thick weld) can be attained when thin contact interface is formed. In this case, the fracture starts in intermetallics-rich zone but propagates mainly in Al-rich melted zone, when in other cases it occurs in brittle intermetallic layers.

Characterization of diffusion-bonded joint between Al and Mg using a Ni interlayer

Aluminum and magnesium were joined through diffusion bonding using Ni interlayer. The microstructure and mechanical performance of the Al/Ni/Mg joints at different temperatures was investigated by means of scanning electron microscope (SEM), electro-probe microanalyzer (EPMA), X-ray diffraction (XRD), Vickers hardness testing, and shear testing. The results show that the addition of Ni interlayer eliminates the formation of Mg–Al intermetallic compounds and improves the bonding strength of the Al/Mg joints. The Al/Ni/Mg joints are formed by the diffusion of Al, Ni and Mg, Ni. The microstructure at the joint interface from Al side to Mg side is Al substrate/Al–Ni reaction layer/Ni interlayer/Mg–Ni reaction layer/Mg substrate multilayer structure. The microhardness of the Mg–Ni reaction layer has the largest value of HV 255.0 owing to the existence of Mg2Ni phase. With the increase of bonding temperature, the shear strength of the joints increases firstly and then decreases. The Al/Ni/Mg joint bonds at 713 K for 90 min, exhibiting the maximum shear strength of 20.5 MPa, which is greater than that of bonding joint bonded directly or with Ag interlayer. The fracture of the joints takes place at the Mg–Ni interface rather than the Al–Ni interface, and the fracture way of the joints is brittle fracture.

Microstructure Characteristic of AZ31/7005 Joints by GTAW with Filler Wire of Mg-Al Alloy

Mg/Al dissimilar materials were welded successfully by GTAW with SAlMg-1 and SAlMg-2 welding wire of Mg-Al system. The nice weld shape and free defects of joints are obtained. The test results indicated that continuous lamellar intermetallic compounds is not found The structure of Mg side in the fusion zone is composed of α-Mg solid solution+ β-Al12Mg17 eutectic structure and precipitates β-A112lMg17 on the grain boundary. The structure in the weld zone is mainly α-Mg solid solution + β-A112lMg17 solid solutions. Mg and Al content are stable in the fusion zone of Mg side. However, in the weld zone of Mg side the Mg content is decreased gradually, and the Al content is increased that reaches a stable level in the weld zone of Al side. As a result, when Mg content in the wire can hold a proper level, the intermetallic compounds will be controlled effectively, and the performance of AZ31/7005 welding joint can be improved.

Molecular dynamics simulation of diffusion bonding of Al–Cu interface

The effects of temperature on diffusion bonding of Al–Cu interface have been investigated by using molecular dynamics (MD) technique with the embedded atomic method (EAM) potentials. The simulated results indicate that the Cu atoms predominantly diffuse into the Al side in the process of diffusion bonding, and the thickness of the interfacial region depends on temperature, with higher temperatures resulting in larger thickness. In the course of diffusion bonding, the interfacial region became disordered. In addition, the Cu atoms diffuse at low ratios but can deeply diffuse into the interior of Al, and the Al atoms diffuse at high ratios but hardly diffuse into the interior of Cu. The results show that the appropriate temperature range for diffusion bonding of Al–Cu interface is 750–800 K, and the diffusion activation energies of Al and Cu are 0.77 eV and 0.50 eV, respectively. Finally, in this work, three diffusion mechanisms of Cu atoms in Al lattice have been found and the main diffusion mechanism is the nearest neighbor hopping mechanism.

A Comparative Study of Friction Stir Brazing and Furnace Brazing of Dissimilar Metal Al and Cu Plates

Friction stir brazing of 5-mm-thick Al and Cu plates in simple lap and stepped lap joint configurations was carried out in air as a modified process for friction stir lap welding of dissimilar metals, in which a pin-free tool and a 0.1-mm-thick Zn braze foil were used to eliminate both pin wear and keyhole and to achieve interface mixing by a metallurgical reaction route instead of vertical plastic mixing, respectively. The microstructure distribution features of friction stir brazing were characterized and compared with traditional furnace brazing to confirm the metallurgical advantages of the new process. For traditional furnace brazing, poor wettability at the Al side for lower brazing temperature or solidification cracking within too thick solidified microstructure (~150 µm) at higher brazing temperature was found. For friction stir brazing, oxide film removal could be achieved well in air without flux by rapid dissolution of the base metals into the molten braze; both solidified microstructure and solidification cracking could be eliminated by extruding excessive liquid phase out of the interface.

Microstructure and Mechanical Properties of Galvanized Steel/AA6061 Joints by Laser Fusion Brazing Welding

Laser fusion brazing welding was proposed. Galvanized steel/AA6061 lapped joint was obtained by laser fusion brazing welding technique using the laser-induced aluminium molten pool spreading and wetting the solid steel surface. Wide joint interface was formed using the rectangular laser beam coupled with the synchronous powder feeding. The result showed that the tiny structure with the composition of α-Al and Al–Si eutectic was formed in the weld close to the Al side. And close to the steel side, a layer of compact Fe–Al–Si intermetallics, including the Al-rich FeAl3, Fe2Al5 phases and Al–Fe–Si τ1 phase, was generated with the thickness of about 10–20 μm. Transverse tensile shows the brittle-fractured characteristic along to the seam/steel interface with the maximum yield strength of 152.5 MPa due to the existence of hardening phases τ1 and Al–Fe intermetallics.

Microstructure and Mechanical Properties in Dissimilar Butt Friction Stir Welding of Severely Plastic Deformed Aluminum AA 1050 and Commercially Pure Copper Sheets

In this study, AA 1050 aluminum alloy and commercially pure copper in annealed and severely plastic deformed conditions were used. The technique used for imposing the severe strain to the sheets was constrained groove pressing (CGP) process. The annealed and severely plastic deformed sheets were subjected to friction stir welding (FSW) at different rotation and traverse speeds. Cu was placed in advancing side. Constant offset of approximately 1 mm was used toward Al side for all welds. A range of welding parameters which can lead to acceptable welds with appropriate mechanical properties was found. For the FSWed CGPed samples, it was observed that the welding heat input caused grain growth and decrease in hardness value at Al side of the stir zone. It was found that, generally the weakest parts of weld joints of annealed and CGPed samples were Al base metal and stir zone, respectively. Further investigations showed that several forms of intermetallic compounds were produced.

Friction stir welding of dissimilar materials between AA6061 and AA7075 Al alloys effects of process parameters

Dissimilar AA6061 and AA7075 alloy have been friction stir welded with a variety of different process parameters. In particular, the effects of materials position and welding speed on the material flow, microstructure, microhardness distribution and tensile property of the joints were investigated. It was revealed that the material mixing is much more effective when AA6061 alloy was located on the advancing side and multiple vortexes centers formed vertically in the nugget. Three distinct zones with different extents of materials intercalations were identified and the formation mechanism of the three zones was then discussed. Grain refinement was observed in all three layers across the nugget zone with smaller grains in AA7075 Al layers. All the obtained joints fractured in the heat-affected zone on the AA6061 Al side during tensile testing, which corresponds very well to the minimum values in microhardness profiles. It was found that the tensile strength of the dissimilar joints increases with decreasing heat input. The highest joint strength was obtained when welding was conducted with highest welding speed and AA6061 Al plates were fixed on the advancing side. To facilitate the interpretation, the temperature history profiles in the HAZ and at zones close to TMAZ were also measured using thermocouple and simulated using a three-dimensional computational model.

Microstructural Evolution and Fracture Behavior of Friction-Stir-Welded Al-Cu Laminated Composites

In this study, we attempt to characterize the microstructural evolution during friction stir butt welding of Al-Cu-laminated composites and its effect on the fracture behavior of the joint. Emphasis is on the material flow and particle distribution in the stir zone. For this purpose, optical microscopy and scanning electron microscopy (SEM) images, energy-dispersive spectroscopy EDS and XRD analyses, hardness measurements, and tensile tests are carried out on the joints. It is shown that intermetallic compounds exist in lamellas of banding structure formed in the advancing side of the welds. In samples welded from the Cu side, the banding structure in the advancing side and the hook formation in the retreating side determine the fracture behavior of the joint. In samples welded from the Al side, a defect is formed in the advancing side of the weld, which is attributed to insufficient material flow. It is concluded that the contact surface of the laminate (Al or Cu) with the shoulder of the FSW tool influences the material flow and microstructure of welds.

Effect of annealing on interface microstructures and tensile properties of rolled Al/Mg/Al tri-layer clad sheets

The aim of this study was to identify the effect of post-roll annealing on the interface microstructure and tensile properties of 1060 pure Al/Mg–0.2Al–1.75Mn–0.75Ce alloy/1060 pure Al tri-layer clad sheets fabricated by a combined hot and cold rolling process. There were no interface reaction phases in the as-rolled clad sheet, and the clad sheet annealed at 200°C for 2h. On annealing at and above 250°C, reaction phases of Al3Mg2 on the Al side and Al12Mg17 on the Mg side were observed to form at the interface. The thickness of interface intermetallic compounds increased markedly with increasing annealing temperature, and exhibited a linear increase with the square root of annealing time, which could be well predicted via diffusion mechanisms. With increasing annealing temperature, the ultimate tensile strength first increased from 200°C to 250°C, where a maximum value of about 160MPa was achieved, then decreased. While the yield strength decreased linearly, the elongation increased significantly with increasing annealing temperature. On annealing at and below 250°C, interface debonding was absent during the tensile tests, while partial debonding occurred via a distinctive mode of zig–zag multiple cracking or fragmentation in the intermetallic compounds in the clad sheets annealed at or above 300°C.

Photoinduced charge injection in the metal/organic interface studied by transient photovoltage measurements with bias

Transient photovoltage of ITO/organic/Al cells is studied under different bias polarities and voltages. It is found that for an ITO/NPB/Al cell, light incidence on the Al side induces more bias-dependent transient photovoltage variation when the photovoltage is positive than when it is negative. However, for an ITO/C60/Al cell, the variation characteristics of transient photovoltage is reversed. These results support the previously proposed mechanism that Al could inject charges into the organic layer upon photon excitation, indicating that the absorption of electrode can also contribute to photovoltaic effect.

Microstructure Characteristics and Properties of Mg/Al Dissimilar Metals Made by Cold Metal Transfer Welding with ER4043 Filler Metal

Abstract AZ31B magnesium alloy and 6061 aluminum alloy were joined in stable welding process by cold metal transfer welding with ER4043 as filler metal. The microstructure, morphology and phase composition of the welded joints were studied by OM, SEM, EDX and XRD. The results show that weld metal and aluminum substrate are combined with a good interface, while weld metal and Mg substrate are combined with a epitaxial solidification area where the intermetallic compounds of Mg 2 Al 3 , Mg 17 Al 12 and Mg 2 Si are generated. The micro-hardness distribution shows a decreasing trend from Mg side to Al side in the weld. The joint is brittle fractured in the fusion zone of Mg side, where plenty of Mg 2 Si, Mg 2 Al 3 and Mg 17 Al 12 are distributed continuously.

An Investigation on Vacuum Brazing of Dissimilar Nonferrous Metals of Cu and Al

The writer successfully obtained brazed Cu-Al joint by using vacuum brazing method, and also conducted an analysis for the microstructure morphology of the joint. The result shows that: The interface of the brazed Cu-Al joint includes three parts---the transition area on the Cu side, the central brazing seam area and the transition area on the Al side. Formed between the brazing seam area and the Cu substrate are the Cu3Al2 and CuAl2 layers, and the average width of the transition area of Cu3Al2 is 12 μm while that of CuAl2 8 μm. The brazing seam area is mainly composed of α-Al solid solution, Cu3Al2 and CuAl2 metal compounds, in addition, the ε-Cu15Si4 phase, the Al-Si phase and CuZn2 phase are also formed. These phases present themselves in the state of acicular compounds, which are dispersed in the brazing seam area.

Microstructural characterization of the Mg/Cu/Al diffusion bonded joint

A vacuum hot-pressed diffusion bonding method was used to prepare an Mg/Cu/Al laminated composite. Both the Mg/Cu and Al/Cu interfaces were investigated by means of scanning electron microscopy, electron probe microanalysis, X-ray diffraction spectrometer system and Vickers microhardness test. The results showed that two kinds of intermetallic compounds, Al4Cu9 adjacent to the Cu side and Al2Cu adjacent to the Al side, were formed in the interface of Al-Cu. Meanwhile, Mg2Cu was formed at the interface of Mg/Cu. The maximum value of shear strength is 13.1 MPa and the fracture of the joints had taken place at the Mg-Cu interface. The microhardness of the interface increased due to the formation of the intermetallic compounds, which is the main cause leading to poor bond properties.

Formation Sequence of Interface Intermetallic Phases of Cold Rolling Cu/Al Clad Metal Sheet in Annealing Process

The formation Gibbs energy of the intermetallic phases at the interface of cold rolling Cu/Al clad metal sheet in annealing process was calculated theoretically. The concept and the calculating method of effective formation Gibbs energy which can predict the formation sequence was proposed. By the means of that theory, the calculated formation sequence of the intermetallic phases at 200-300 was worked out for the cold rolling Cu/Al clad metal sheet in annealing process, i.e. Al2Cu (Al side), AlCu (mid-layer) and Al4Cu9(Cu side). Besides, the boundary layer organizational microstructure of the composite material was analyzed by the means of SEM and XRD. As a result, the annealing temperature is the primary factor which affects the formation of the intermetallic phases of the cold rolling Cu/Al clad metal sheet, while the holding time is the second one. The observed formation sequence of the intermetallic phases of cold rolling Cu/Al clad metal sheet on annealing temperature 250-300 was: Al2Cu (Al side), Al4Cu9(Cu side) and AlCu (mid-side).

듀오캐스트 Al-Mg-Si/Al 하이브리드 합금의 미세조직과 기계적 변형 특성

Al-Mg-Si/Al hybrid alloy was prepared by Duo-casting and the mechanical behavior was evaluated based on their microstructure and mechanical properties. The hybrid aluminum alloy included the Al-Mg-Si alloy with fine eutectic structure, pure Al with the columnar and equiaxed crystals, and the macro-interface existing between Al-Mg-Si alloy and pure Al. The growth of columnar grains in pure Al occurred from the macro-interface. The tensile strength, 0.2% proof stress and bending strength of the hybrid aluminum alloy were almost similar to those of pure Al, and the elongation was much higher than the Al-Mg-Si alloy. The fracture of the hybrid alloy took place in pure Al side, indicating that the macro-interface was well bonded and the mechanical behavior strongly depends on the limited deformation in pure Al side.