Alloy Thick Plate Research Articles

P92钢与Inconel 625合金厚板超窄间隙激光填丝焊接头的组织与性能

P92钢与Inconel 625合金厚板超窄间隙激光填丝焊接头的组织与性能

Calculation and experimental study on heating temperature field of super-high strength aluminum alloy thick plate

Abstract Stepped heating treatment has been applied to aluminum alloy thick plate to improve the mechanical performance and corrosion resistance. Accurate temperature control of the plate is the difficulty in engineering application. The heating process, the calculation of surface heat transfer coefficient and the accurate temperature control method were studied based on measured heating temperature for the large-size thick plate. The results show that, the temperature difference between the surface and center of the thick plate is small. Based on the temperature uniformity, the surface heat transfer coefficient was calculated, and it is constant below 300 °C, but grows greatly over 300 °C. Consequently, a lumped parameter method (LPM) was developed to predict the plate temperature. A stepped solution treatment was designed by using LPM, and verified by finite element method (FEM) and experiments. Temperature curves calculated by LPM and FEM agree well with the experimental data, and the LPM is more convenient in engineering application.

Anisotropy in fatigue crack propagation behavior of Al-Cu-Li alloy thick plate

Anisotropy in fatigue crack propagation (FCP) behavior of Al-Cu-Li-T87 alloy thick plate is investigated by means of optical microscopy (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron back scattering diffraction (EBSD) in the present work. Results show that FCP rates of the three orientations show distinct difference. Grain size and boundary, coarse inclusion particles, precipitates and grain orientations are capable of affecting the fatigue performance, but coarse inclusion particles and T1 precipitates are found to be the main factors in determining the fatigue performance. Grain boundaries of pan-caked grain structure fail to impede the fatigue crack growth effectively because of the coarse inclusion particles and precipitates along grain boundaries. Fatigue cracks easily propagate along the grain boundaries, therefore result in a low FCP resistance. In addition, Brass grains can induce crack deflection due to the relative large twist angle of grain boundaries between Brass grain and neighboring grain when considerable T1 precipitates are observed in Al-Cu-Li alloy.

Microstructural characterization of 5083 aluminum alloy thick plates welded with GMAW and twin wire GMAW processes

Thick plates of 5083 aluminum alloy are welded with GMAW and GMAW-TW processes; the influence of weld pool convection on porosity formation, microstructure, and mechanical property of the welding joints is investigated. The results showed that due to the appearance of outward flow and “push-pull” patterns, and intense mixing and stirring effects in GMAW-TW process, a sound weld seam with less porosity can be obtained. The less probability of bubble formation, the shorter escaping distance of the bubble, the easy splitting of bubble, the higher bubble escape velocity, and lower solidification rate are responsible for porosity suppression. Even though the grain size in GMAW-TW process is larger than that in GMAW process, the ultimate tensile strength of the joints is larger, which is caused by less porosity formation, larger number, and uniform distribution of second-phase particles in the welds. Compared with GMAW process, the GMAW-TW process possesses the advantages of higher efficiency, less weld defects, and higher mechanical property in the welding of 5083 aluminum alloy thick plates.

Precipitation Kinetics Analysis of the Cooling Process Following the Solid Solution Treatment of 7B50 Aluminum Alloy

Based on the TTP curves of 7050 alloy, and the continuous cooling curves of 7B50 alloy at different positions of Φ70 mm improved Jominy specimen, the hardness distribution along the thickness direction of 7B50 alloy thick plates was analyzed and predicted by means of the isothermal precipitation kinetics and the quench factor analysis method. The results show that when 7050 alloy is isothermal treated at 200°C~400°C, the exponent n in its Johnson-Mehl-Avrami equation is close to 1, which indicates that the nucleation process of new precipitates is stable. In this equation the coefficient k is 7.420E-03 at 350°C, which indicates that the nucleation and growth rates of new precipitates are very fast. The hardness distribution along the axial direction of the improved Jominy specimen of 7B50 alloy is predicted by the quench factor analysis method. When the distance is no more than 65 mm from the spraying surface of the improved Jominy specimen, the deviation between the predicted and measured hardness of 7B50 alloy in T6 temper is less than 5%. The quench factor analysis method is feasible to predict the hardness distribution along the thickness direction of 7B50 alloy thick plates after quenching and aging. When the quench factor analysis method is extended to predict the actual water spray quenching process of 7B50 alloy thick plates, the average cooling rate is 21.6°C/s in the quench sensitive temperature range of this alloy, at 15 mm from the spraying surface of the plate. At the same position, the corresponding quench factor is equal to 6 and the predicted hardness is 187.4 HV which is equivalent 98.5% of the Hmax (the maximum hardness) of 7B50 alloy in T6 temper.

Corrosion Behavior of Top and Bottom Surfaces for Single-Side and Double-Side Friction Stir Welded 7085-T7651 Aluminum Alloy Thick Plate Joints

Thick plate joints of 7085-T7451 aluminum alloy were obtained through both single-side and double-side friction stir welding (SS or DS-FSW). The chloride ions effects on the corrosion behavior of the top and bottom surfaces of the joints were examined by cyclic potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM). Results show that the corrosion susceptibility was suppressed significantly in the weld nugget zone, while the base material and heat-affected zone were prone to be corrosion attacked. For the SS-FSWed joint, the top surface showed a higher corrosion resistance than that of the bottom surface, but the larger corrosive heterogeneity was observed between the top and bottom surfaces compared with the two welds of DS-FSWed joint, which was confirmed by the morphology of corrosion attack. A deep insight on the microstructure of the joints indicates that the intermetallic particles played a key role in the corrosion behavior of the FSWed AA7085 aluminum alloy joints in chloride solution.

Microstructure and mechanical properties in friction stir welded 5A06 aluminum alloy thick plate

Friction stir double-sided butt welding was carried out for the joining of 5A06 aluminum alloys with thickness of 108mm, and sound welds with full penetration were produced. Microstructure characterizations of the welding joint were investigated by optical microscopy, electron back-scattered diffraction and transmission electron microscopy (TEM). The results indicate that void defects are observed in shoulder-affected zone (SAZ) and grain size of equiaxed grains in SAZ and weld nugget zone (WNZ) decreases gradually along the thickness direction, while in SAZ the dislocation density is significantly lower and the sub-grain size is much larger than those in WNZ. Microhardness surveys reveal that on the upper part of the joint hardness profile presents a “V” shape and minimum hardness appears in SAZ whereas that in other regions exhibits a “W” shape and the lowest hardness value occurs in the heat-affected zone adjacent to the advancing side. The investigation of tensile properties on the FSW joint indicates the WNZ exhibited superior tensile properties compared with SAZ, and the analysis of fracture surface using the scanning electron microscopy (SEM) demonstrates that fractures in all tensile specimens are ductile fracture due to the presence of dimples with different sizes.

Investigation on Residual Stresses in Pre-Stretching Process of Aluminum Alloy Thick Plate Based on Material Non-Uniformity

A discretization method is used in pre-stretching simulation to separate an aluminum alloy thick plate into layers. When the equivalent plastic strain in each layer is defined according to the residual stresses during quenching, the yield strength model can be developed to estimate its yield strength. Again, the curve of elasticity modulus is fitted in the light of the experimental data, which can reveal how the elasticity modulus changes with plastic deformation. Finally, in consideration of the non-uniformity of yield strength and elasticity modulus, the pre-stretching of the quenched 7075 aluminum alloy thick plate is taken as an example to numerically simulate the value and distribution of residual stresses at the pre-stretching ratio of 1.8%, 2.2% and 2.5%, respectively. It is known from the simulated results that, by using the proposed method in this paper, the obtained results of the distribution and magnitude of the residual stresses are in good agreement with the experimental measurements.

Analysis of temperature asymmetry of aluminum alloy thick plate during snake hot rolling

In order to study the temperature distribution of aluminum alloy thick plate during snake hot rolling, several coupled thermo-mechanical models using finite element method (FEM) were established. Effects of different factors on temperature distribution of the plate and the bending behavior due to temperature difference were analyzed. Temperature asymmetry coefficient was defined in this study. The results show that the temperature distribution of plate is asymmetrical and the temperature of the lower surface is higher than the upper surface during snake hot rolling, in which the maximum α can gd reach 58 °C/m. The asymmetric coefficient was increased with the increase of rolling velocity and speed ratio. Different ways of heat exchange play different roles in the temperature distribution. Friction heat and deformation heat play dominant role in hot rolling process and pass interval time and their weight influences were 47 and 69 %, respectively. The bending curvature is increased with the increase of temperature difference and pass reduction and decreased dramatically with the increase of initial thickness. The FEM results agree well with experimental results.

Study of Pre-stretching Fracture for Aluminum Alloy Thick Plates with Defects

Study of Pre-stretching Fracture for Aluminum Alloy Thick Plates with Defects

Residual stress relief in Al–Zn–Mg–Cu alloy by a new multistage interrupted artificial aging treatment

A novel multistage interrupted artificial aging treatment was designed for reducing residual stresses in quenched Al–Zn–Mg–Cu alloy thick plates. The results show that residual stress magnitudes were reduced significantly and even eliminated completely by this novel treatment while the conventional artificial aging only contributed to a reduction 10%-35%, because an inverse stress was ingeniously employed during rapid heating to release the internal residual stress. Meanwhile, the mechanical properties were maintained, and the corrosion resistance was improved comparing to conventional artificial aging. The maintained mechanical property and improved corrosion resistance were resulted from rearranging of dislocations and precipitates characters in multistage interrupted artificial aged alloys.

Effect of tool rotational speed on residual stress, microstructure, and tensile properties of friction stir welded 6061-T6 aluminum alloy thick plate

In the present study, the effect of tool rotational speed on residual stress, microstructure, and tensile properties of friction stir welded AA 6061-T6 was investigated. AA 6061-T6 plates with a thickness of 16 mm were friction stir welded using three different tool rotational speeds of 500, 700, and 900 rpm and a constant welding speed of 120 mm/min. The results indicate that the longitudinal residual stress distribution is an M-shaped distribution in the transverse direction; in weld region, the tensile longitudinal stress in the advancing side is larger than that in the retreating side. With increasing rotation speed, the values of the tensile longitudinal residual stresses increased slightly, the peak tensile longitudinal stresses appear at the edge of the shoulder in the AS of the joints, and the maximum value of tensile longitudinal residual stress was 153 MPa with the rotation speed of 900 rpm which reaches up to 55 % of the yield strength of AA 6061-T6. Meanwhile, only the appearance of welded joint with 700 rpm is smooth. The grain size in WNZ grows up with increasing the rotation speed. The microhardness variation is determined by microstructure evolution, and the average microhardness decreases with increasing the rotation speed. The welded joint with the rotation speed of 700 rpm performs the maximum tensile strength of 236 MPa which is 76 % of the base material strength.

Influence of Test Temperature on the Tensile Properties along the Thickness in a Friction Stir Welded Aluminum Alloy

The aim of this study was to evaluate microstructures and the influence of test temperature on the tensile properties, strain hardening behavior and fracture characteristics of friction stir welded (FSWed) 2219-T62 aluminum alloy thick plate joints. A fine and equiaxed recrystallized grain structure had no significant change in grains at the top of weld nugget zone (WNZ) at a rotational rate of 500 r/min compared with 300 r/min, but the grains and second-phase particles at the middle of WNZ exhibited obvious coarsening. The yield strength, ultimate tensile strength and joint efficiency were observed to decrease with increasing test temperatures. However, the elongation presented a contrast trend. Compared with the middle and bottom slices, the top slice (216 and 342 MPa) had a higher strength and a lower elongation (8.5%) at different test temperatures. Hardening capacity and strain hardening exponent of bottom slices were higher than those of the top and middle slices. Both of them at room temperature (RT) were bigger than those at higher temperature (HT) and lower temperature (LT). The FSWed joints basically failed in the border area between the thermo-mechanical affected zone (TMAZ) and heat-affected zone (HAZ) of the top slice, and in the HAZ of the middle or bottom slices, while the fracture surfaces exhibited dimple fracture characteristics at different test temperatures.

Through-thickness inhomogeneity of localized corrosion in 7050-T7451 Al alloy thick plate

The through-thickness corrosion inhomogeneity of 7050-T7451 Al alloy thick plate was studied using immersion tests, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), slow strain rate testing (SSRT) technique combined with optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that the through-thickness corrosion resistance is ranked in the order of T/2>surface>T/4. And the 75 mm-thick 7050 alloy plate presents better corrosion resistance than the 35 mm-thick plate. The results are discussed in terms of the combined effect of recrystallization and cooling rate in quenching. Alloy with lower volume fraction of recrystallization and smaller grain aspect ratio displays better corrosion resistance. The lower corrosion resistance caused by the slower cooling rate results from the higher coverage rate of grain boundary precipitates and larger width of precipitate free zone.

Microstructure and mechanical properties of friction stir welded AA7075–T651 aluminum alloy thick plates

Friction stir butt welding of AA7075–T651 plates with thicknesses of 10 and 16 mm was investigated. Defect-free, full-penetration welds were obtained after careful process parameter selection. While the nuggets in both welds exhibited very fine recrystallized grains, and finer grains were observed in welds made on 10 mm thick plates. Microhardness surveys revealed that significant loss in hardness occurs in the heat-affected zone. The reduction in hardness due to the welding process is higher in the case of welds made on 16 mm thick plates. Welds made on 10 mm thick plates exhibited superior tensile properties compared with those made on 16 mm thick plates. Fracture during tensile test occurred in the heat-affected zone in both cases. TEM images of specimens revealed that the heat-affected zone consisted of widened precipitate-free zones along grain boundaries and partial dissolution of precipitates in the grain interiors. It is concluded that defect-free single pass welds can be made on AA7075–T651 thick plates using friction stir welding and the welds made on 10 mm thick plates exhibit high joint efficiency.

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.

404 半連続鋳造法で作製したマグネシウム合金厚板の熱間鍛造(OS4-(1),OS4 オーガナイズドセッション≪材料・組織と加工≫)

This study revealed the possibility of hot forging of AZ131 magnesium alloy thick plate prepared by semi-continuous casting method. Semi-continuous casting process has a beneficial effect on producing thick plate for forging. AZ131 magnesium alloy has high strength and quite small elongation compared the general plastic magnesium alloy, however the forging ability of AZ131 is not clear. Pin type die was used to research the forging ability of AZ131 magnesium alloy. Results are below. It was possible to forge the AZ131 magnesium alloy thick plate prepared by semi-continuous casting. Some cracks were observed on the surface of forging at 350℃. Cracks were free on the surface of forging at 300℃ and the AZ131 magnesium alloy were filled up in the die. It was suggested that forging at lower temperature was effective to prevent the cracking.

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.

Fracture toughness and fatigue crack growth analysis of 7050-T7451 alloy thick plate with different thicknesses

The strength, fracture toughness and fatigue crack growth resistance of 7050-T7451 aluminum alloy plate with different thicknesses (35 mm and 160 mm) were investigated by means of optical microscope, scanning electron microscope and transmission electron microscope. The results show that thicker plate has lower strength and fracture toughness but higher fatigue crack growth resistance, by comparison to the thinner plate. The drop of strength is mainly attributed to grain coarsening in the thicker plate, and the increased degree of recrystallization results in the loss of KIC. However, the coarsened grains in the thicker plate make cracks deflected and closure effect enhanced due to surface roughness increased. For both of plates, in the fracture surface subjected plain strain, a transition from transgranular dimpled fracture to intergranular dimpled fracture is observed during the fracture process.

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.