Aluminum Alloy Thick Plate Research Articles

면외변형의 영향을 받는 알루미늄합금 일면전단 볼트접합부의 내력평가에 관한 실험적 연구

Many researchers have studied the structural performance of bolted connection with aluminum alloys and design specifications for in-plane fracture (net-section, bearing and block shear fractures) of bolted connection have been improved by their study results. However, it can be known from study results conducted by Kim et al. that curling (out-of-plane deformation) could be negative effect (strength reduction) on ultimate strength of single shear bolted connection fabricated with 3.0mm thick aluminum alloy(6061-T6) plate. Strength reduction for curled single shear specimens obtained from the comparison of test results for double shear bolted connections ranged from 4% to 30%. In this paper, additional experiments are performed in order to investigate the influence of curling on ultimate strength and curling occurrence condition for 4.0mm thick bolted connection. Main variables are end distance and edge distance. In all specimens, strength reduction by curling was observed. Strengths obtained from test results were compared with design strengths predicted by AISI (American Iron and Steel Institute) and AAA (American Aluminum Association) design rules. Bearing factor considering curling effect and hole deformation limit was discussed.

Effect of tool traverse speed on microstructure and mechanical performance of friction stir welded 7020 aluminum alloy

The effect of tool traverse speed on microstructure and mechanical properties of friction stir welded 7020-T6 aluminum alloy was investigated. For this purpose, 5 mm thick 7020-T6 aluminum alloy plates were friction stir welded at traverse speeds of 50, 100, 150, and 200 mm/min and constant rotational speed of 900 r/min. Also, the peak temperatures of the joints during friction stir welding were recorded by accurate thermocouples. Moreover, the microstructure, hardness, tensile properties, and fracture surfaces of the joints were examined. The results showed that increasing the tool traverse speeds from 50 to 200 mm/min decreased the peak temperature from 331 ℃ to 211 ℃, and hence caused to lower heat input during friction stir welding. Furthermore, the higher hardness and ultimate tensile strength of the joints welded at higher traverse speeds was related to the grain boundary, precipitation, and substructure strengthening mechanisms. In addition, the fracture surfaces of the joints welded at higher heat input conditions showed more ductile mode in comparison with those welded at lower heat input condition, which confirmed the lower tensile elongation of the joints welded at higher traverse speeds.

Quench induced residual stress prediction in heat treatable 7xxx aluminium alloy thick plates using Gleeble interrupted quench tests

In this paper, a simple but realistic approach is presented to predict the as-quenched residual stress distribution in thick 7xxx aluminium alloy plates. Instead of modelling precipitation that occurs during quenching, a thermo-mechanical model is used whose parameters are identified using a limited number of tensile tests achieved after representative interrupted cooling paths in a Gleeble machine. The material behaviour law accounts for recovery at high temperature in a simple way and neglects the Bauschinger effect as suggested by a dedicated experiment. The results of this simple approach are compared to residual stress measurements in plates of different thicknesses for two different 7xxx alloys, AA7449 and AA7040.

Effect of tool rotational speed on force generation, microstructure and mechanical properties of friction stir welded Al–Mg–Cr–Mn (AA 5052-O) alloy

Friction stir welding (FSW) between 3 mm thick AA 5052-O aluminum alloy plates was investigated in the present study. Different welded specimens were produced by employing a constant tool traverse speed of 120 mm/min and by varying rotating speeds from 800 to 3000 rpm. The welded joints were characterized by its appearances, microstructural and mechanical properties at room temperature. The measurement of different forces acted on the tool during the FSW of AA 5052-O plates provided a significant insight to determine the quality of the welded joints. From the appearances of the welded joints it was evident that, except the tool rotational speed of 3000 rpm all other rotational speeds produced sound welded joints with smooth surface. The joint produced at 1000 rpm yielded a maximum tensile strength of 132 MPa which was 74% of the base material strength. Field emission scanning electron microscopy (FESEM) and energy dispersive spectroscopy (EDS) analyses on the stir zone suggested that, β-Mg2Al3 intermetallic phases of the base material were mechanically fractured, smeared and mixed to different geometries due to tool stirring. The dissolution and redistribution of β-Mg2Al3 second phase particles in the stir zone had a considerable effect on the reduction of the tensile strength of the welded joints. The reduction in hardness at the nugget zone (NZ) of the welded joints under different tool rotational speeds could be attributed to the dislocation of Mg-rich phases and segregation of Mg solute atoms at grain boundaries, which drew solute Mg atoms away from the α-aluminum matrix.

Deformation Rule of 7150 Aluminum Alloy Thick Plate by Pre-Stress Shot Peen Forming

Pre-stress shot peen forming is a metal forming process widely used in aeronautical industry. The test parts of 7150 Al alloy of different thickness were pre-stress shot peen formed. The deformation rule of those parts was investigated by means of changing the peening coverage. The results show that the radius of curvature of the parts will enhance gradually with increasing of the plate’s thickness. In addition, enhancing peening coverage could raise the deformation in the case of that the thickness and peening parameters are unchanged. Furthermore, the minimum radius of curvature of the 8mm plate after saturation pre-stress shot peen forming could reach 499mm.

Analysis of Quenching and Stretching Processes of Aluminum Alloy Thick Plates

7050 aluminum alloy thick plates are usually heat treated and then aged to improve mechanical properties; however, residual stresses in the plates are developed during quenching. In this study, the influences of non-uniform factors on residual stresses in aluminum alloy thick plates during the quenching and stretching processes are studied. The results show strong inhomogeneity of the residual stress distribution in the plates, and the length of influenced area of the stretched plate is discussed.

Fatigue crack growth behaviour of friction stir welded AA7075-T651 aluminium alloy joints

The aim of the present work is to evaluate the fatigue crack growth behaviour of 12 mm thick AA 7075-T651 aluminium alloy plates joined by FSW. Fatigue crack growth test was carried out on center cracked tensile (CCT) specimens extracted from the FSW joints and unwelded parent metal. Transverse tensile properties of the unwelded parent metal and welded joints were evaluated. Microstructures of the welded joints were analyzed using optical microscopy and transmission electron microscopy. The scanning electron microscope was used to characterize the fracture surfaces. It was found that the ΔKcr of the welded joint is reduced by 10×10−3 MPa·m1/2 in comparison with the unwelded parent metal. Hence, the fatigue life of the friction stir welded AA 7075-T651aluminium alloy joints is appreciably lower than that of the unwelded parent metal, which is attributed to the dissolution of precipitates in the weld region during friction stir welding.

Shear deformation and plate shape control of hot-rolled aluminium alloy thick plate prepared by asymmetric rolling process

Asymmetric rolling (ASR), as one of severe plastic deformation (SPD) methods to make ultra-fine materials with enhanced performance is mainly used to prepare foil and thin strip. The asymmetrical rolling was achieved by adjusting the diameters of the upper roll and the bottom roll and was used to prepare hot-rolled thick plate of 5182 aluminium alloy. The shear deformation and plate shape control were experimentally studied. The experimental results show that asymmetrical rolling has a significant effect on metal deformation stream and can somehow refine microstructure and improve the uniformity of microstructure and properties. The asymmetrical rolling process can also reduce the rolling force. However, bending of rolling plate often happens during asymmetrical rolling process. The factors affecting the bending were discussed.

Non-isothermal retrogression kinetics for grain boundary precipitate of 7A55 aluminum alloy

The retrogression kinetics for grain boundary precipitate (GBP) of 7A55 aluminum alloy was investigated by transmission electron microscopy (TEM) observation. The results reveal that the coarsening behavior of GBP obeys “LSW” theory, namely, the cube of GBP average size has a linear dependence relation to retrogression time, and the coarsening rate accelerates at the elevated retrogression temperature. The GBP coarsening activation energy Qd of (115.2±1.3) kJ/mol is obtained subsequently. Taking the retrogression treatment schedule of 190 °C, 45 min derived from AA7055 thin plate as reference, the non-isothermal retrogression model for GBP coarsening behavior is established based on “LSW” theory and “iso-kinetics” solution, which includes an Arrhenius form equation. After that, the average size of GBP r(t) is predicted successfully at any non-isothermal process T(t) when the initial size of GBP r0 is given. Finally, the universal characterization method for the microstructure homogeneity along the thickness direction of 7A55 aluminum alloy thick plate is also set up.

Effect of tool pin eccentricity on microstructure and mechanical properties in friction stir welded 7075 aluminum alloy thick plate

Four different tools with the pin eccentricity of 0.1mm, 0.2mm, 0.3mm and 0.4mm were designed to friction stir weld 10mm thick AA7075-O plate. The effect of pin eccentricity on microstructure, secondary phase particles transformation and mechanical properties of the joints was investigated. The results show that the nugget area (ANZ) increases firstly and then decreases with increasing the pin eccentricity. When the pin with 0.2mm eccentricity is applied, the ANZ is the largest; meanwhile the grains size is the smallest which is about 3μm and secondary phase particles are the most dispersive in nugget zone compared with other tools. While the grains are coarsened to 7–11μm as the eccentricity is more than 0.4mm, some coarse hardening particles get to cluster in the thermo-mechanically affected zone. The joints produced by the pin with 0.2mm eccentricity perform the highest tensile strength and elongation, which is attributed to better interfaces, finer grains and more dispersive secondary phase particles.

Unifying Monotonic and Hysteresis Material Properties for Notch Plasticity Analysis under Variable Amplitude Loads

This study was performed in support of accurate notch plasticity analysis under variable amplitude loads. Monotonic and cyclic strain-controlled tests were performed on flat dog-bone coupons machined from 6.35mm thick 7075-T651 aluminium alloy plates. The tests with low-high-low strain amplitude transitions revealed both an instant softening following the high strain amplitude cycle and a gradual recovery during the subsequent low strain amplitude cycles. The transition from monotonic-like to hysteresis-like material behaviour was found to be consistent with an overload induced softening and recovery process. A conceptual consideration is thus proposed to unify the characterisation of monotonic and hysteresis material properties. The implications of the present finding on notch plasticity analysis are also discussed.

Improvement in Fatigue Strength of Friction Stir Welded Aluminum Alloy Plates by Laser Peening

Plane bending fatigue testing was performed to study the fatigue properties of friction stir welded (FSW) 3 mm thick AA6061-T6 aluminum alloy plates. Fatigue cracks propagated with bends and curves on the specimens, showing large deviation from a linear line. This might be reflecting the material flow and microstructure in the weld zone. The fatigue strength of the unwelded base material (BM) was 110 MPa at 107 cycles and FSW deteriorated it to 90 MPa. However, laser peening (LP) restored the degraded fatigue strength up to 120 MPa which is higher than that of the BM.

Analysis of Stretching Load in Tension Stretching Process of Aluminum Alloy Thick-Plate by Using Finite Element Method

Tension stretching process is an important link in production of aluminum alloy thick-plate. Exploring the change of load in tension stretching process is important for the structure designing and key component checking of large-scale tension stretcher. In this paper, the changing law of stretching force in the tension stretching process of aluminum alloy 6063 thick-plate has been investigated by numerical simulation method, and the influence of initial thickness of plate and friction condition in clamping area was analyzed. The results indicated that the initial thickness has a notable influence but friction condition has a little influence on stretching load; and the stretching force increases at first and then decreases slightly, and then it is tending toward stability; and the larger the values of thickness and friction, the more stable the stretching force in the process.

Analysis and Comparison of Friction Stir Welding and Laser Assisted Friction Stir Welding of Aluminum Alloy.

Friction Stir Welding (FSW) is a solid-state joining process; i.e., no melting occurs. The welding process is promoted by the rotation and translation of an axis-symmetric non-consumable tool along the weld centerline. Thus, the FSW process is performed at much lower temperatures than conventional fusion welding, nevertheless it has some disadvantages. Laser Assisted Friction Stir Welding (LAFSW) is a combination in which the FSW is the dominant welding process and the laser pre-heats the weld. In this work FSW and LAFSW tests were conducted on 6 mm thick 5754H111 aluminum alloy plates in butt joint configuration. LAFSW is studied firstly to demonstrate the weldability of aluminum alloy using that technique. Secondly, process parameters, such as laser power and temperature gradient are investigated in order to evaluate changes in microstructure, micro-hardness, residual stress, and tensile properties. Once the possibility to achieve sound weld using LAFSW is demonstrated, it will be possible to explore the benefits for tool wear, higher welding speeds, and lower clamping force.

A study on friction stir welding of 12mm thick aluminum alloy plates

Most of the investigations regarding friction stir welding (FSW) of aluminum alloy plates have been limited to about 5 to 6 mm thick plates. In prior work conducted the various aspects concerning the process parameters and the FSW tool geometry were studied utilizing friction stir welding of 12 mm thick commercial grade aluminum alloy. Two different simple-to-manufacture tool geometries were used. The effect of varying welding parameters and dwell time of FSW tool on mechanical properties and weld quality was examined. It was observed that in order to achieve a defect free welding on such thick aluminum alloy plates, tool having trapezoidal pin geometry was suitable. Adequate tensile strength and ductility can be achieved utilizing a combination of high tool rotational speed of about 2000 r/min and low speed of welding around 28 mm/min. At very low and high dwell time the ductility of welded joints are reduced significantly.

Influence of mechanical behavior between the grains on stress fluctuation of aluminum alloy thick plate

The research on fl uctuation and inhomogeneity of internal stress of aluminum alloy thick plate is theoretical and technological base for stress control technology. By using X-ray diffraction technique and mechanical test method, aluminum alloy with typical fine sub-grains, coarse recrystallized grains, and second phase was analyzed; the interactive mechanical model between grains was built for analysis of variation of internal stress within the local micro structure by imitating the actual distribution of grains. The experimental result shows that the mechanical model can effectively explain the reason for fluctuation of microscopic stress, which also proves that the inhomogeneous distribution of metal organization is the cause for the complex distribution of microscopic stress. The model can well describe stress distribution of thick plate caused by thermal deformation. Besides, it well describes mechanism of stress fluctuation.

Effect of retrogression and reaging treatment on the microstructure and fatigue crack growth behavior of 7050 aluminum alloy thick plate

Effect of Retrogression and Reaging (RRA) treatment on the microstructure and fatigue crack growth behavior of 7050 aluminum alloy thick plate was investigated by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD). The results showed that the RRA microstructure is similar to that for T6 treatment inside the grains, but is slightly denser and coarser and more stable in nature. Also grain boundaries precipitates (GPBs) coarsen obviously, distributing discontinuously and isolated. The precipitation free zones (PFZs) are broadened than that of the T6 sample, and narrower than that of the T7451 sample. And maintaining strength equal to that for the T6 peak-aged treatment and enhanced fatigue crack growth resistance to that for the T7451 overaged treatment can be achieved for RRA treatment.

Effect of Welding Speed on CO<sub>2</sub> Laser Beam Welded Aluminum-Magnesium Alloy 5083 in H321 Condition

Laser beam welding of aluminum alloys is expected to offer good mechanical properties of welded joints. In this experimental work reported, CO2 laser beam welding at 3.5 kW incident power was conducted autogenously on 5 mm thick 5083-H321 aluminum alloy plates at different welding speeds. The mechanical properties and microstructural characteristics of the welds are evaluated through tensile tests, micro-hardness tests, optical microscopy and scanning electron microscopy (SEM). Both yield stress and tensile strength of the laser beam welded joint at the optimum welding speed were 88 % of base metal values. Experimental results indicate that the tensile strength and hardness of laser beam welds are affected by the variation of the intermetallic compounds.

Influence of welding parameters and tool pin profile on microstructure and mechanical properties along the thickness in a friction stir welded aluminum alloy

Microstructure, second-phase particles and mechanical properties of the joint along the thickness of plate during friction stir welded 2219 aluminum alloy thick plate using different shapes pin were investigated in this paper. The top presented larger equiaxed recrystallized grain structure and finer second-phase particles compared to the middle and bottom. Thermo-mechanically affected zone and boundary were more optically distinct on the advancing side in comparison with the retreating side. Grain size and particles were much finer and dispersed using the first tool with three spiral flute or at the lower rotational speed of 300rpm. The strength and ductility in top slices was slightly higher than that in middle and bottom, increased with increasing traverse speed from 60 to 100mm/min or the decrease of rotational speed from 500 to 300rpm using the first tool. The mechanical properties using the second tool was lower than that of first tool, which was consistent with the hardness curves.

To Research Residual Stress Using Finite Element Analysis

The residual stress distributions of 7075 aluminum alloy rectangular thick plates after quench-hardening had been simulated firstly, then all the results were presented and compared with each other. Some deep theoretical analyses were also carried out. The results show that complicated residual stress distribution regularities in aluminum alloy thick plates can be obtained by the finite element analysis successfully.