International Journal of Lightweight Materials and Manufacture最新文献

The main purpose of this study is to investigate the influence of retrogression and re-aging post weld heat treatment (RRA-PWHT) on potentiodynamic corrosion (PC) and stress corrosion cracking resistance (SCC) of stir zone (SZ) of AA7075-T651 alloy butt joints developed using friction stir welding (FSW). FSW was employed to overcome the problems in fusion welding of AA7075-T651 alloy such as solidification cracking, heat affected zone (HAZ) softening, grain coarsening, dissolution of strengthening precipitates and inferior mechanical performance. The SZ of joints were subjected to potentiodynamic corrosion test in 3.56 wt% NaCl solution. The circumferential notch tensile (CNT) specimens were subjected to SCC test at various conditions of axial stress level in 3.56 wt% NaCl solution. The microstructural features of butt joints SZ were characterized using optical (OM), scanning electron (SEM) and transmission electron microscope (TEM). The results disclosed that RRA-PWHT joints exhibited greater PC and SCC resistance compared to as-welded joints. The threshold stress level for the failure of CNT specimens of parent metal, as-welded joints and RRA-PWHT joints was 242 MPa, 175 MPa and 198 MPa, respectively. The threshold stress level of RRA-PWHT joints and as-welded joints is 81.81% and 72.31% of parent metal threshold stress level. It is correlated to increase in vol% and coarsening of grain boundary precipitates with enrichment of copper at the grain boundaries.

Nowadays, surface modification techniques are a big part of making metals and alloys better on the outside. Even though various metals and alloys are coated using surface modification techniques, improving the surface properties of the light alloys is difficult. To improve the surface properties of light alloys, electro-thermal techniques, namely electro discharge deposition (EDD), are suitable. Hence, in this investigation, a fly ash (FA)–copper (Cu) composite coating was developed on AA7075 using electro discharge deposition. The FA–Cu composite electrodes were manufactured by the powder metallurgy method. The effects of discharge current, pulse on time, and pulse off time on deposition rate (DR) and coating roughness (CR) have been studied. Tests were carried out according to the design matrix generated by central composite design in response surface methodology (RSM). An ANOVA was performed to determine the optimum parametric conditions for the responses. Pulse off time was the dominating parameter followed by discharge current and pulse on time for attaining the best response. Higher values of current, pulse on time, and pulse off time led to higher DR and CR values. Higher discharge current produced sufficient spark strength that melted both the tool electrode and the workpiece. The lower setting of parameters offered smooth roughness due to the even spark distribution. At a current of 8 A, bigger craters were observed due to the higher spark intensity that made the surface hard. The uneven mass was produced with a deeper shallow crater, resulting in a poor surface.

In this paper, a novel method was proposed to improve the production efficiency and formability of titanium alloy, which was named triple-layer sheet hot stamping with a cold die cooling (THF). The titanium alloy sheet was clamped by two steel sheets with no adhesive added, then heated, transferred and formed together. In order to verify the ability in enhancing formability of this process, spherical part forming tests were carried out to study the formability under the single-layer sheet hot stamping (SHF) and THF. Finally, a plug socket part was formed to verify the practicability of the novel forming process. The finite element (FE) model was established to analyze the forming process finding that the formability of the parts were significantly improved after using THF process. Comparing with SHF process, the stamping depth increases by 135.7% at 900 °C in the THF process. The forming limit strain increases from 0.18 of the single-layer sheet to 0.51 of the triple-layer sheet. The forming limit strain obtained by the THF process is close to that of isothermal forming. The friction state is one of the main reason for improving formability. Moreover, for plug socket parts, there is almost no thinning of the part in the THF process at 900 °C. In conclusion, it has great advantages in improving the formability of titanium alloy using the THF process.

This study investigates the optimization of 3D printing and CO₂ laser cutting parameters by the design of experiments (DOE) and response surface methodology (RSM). In fused filament fabrication (FFF) process, the surface quality of printed curves is poor due to the stairstep defects. The aim is to determine how the laser cutting parameters affect the surface morphology of surface finishing polylactic acid (PLA) samples. A total of 13 cube shape samples are 3D-printed with a cone-shaped hole in the middle. Then, post-processing CO₂ laser cutting with a maximum power of 1 kW is used to cut the 3D-printed products. Infill percentage (IP) and extruder temperature (ET) in 3D printing, and laser power (LP), scanning speed (SS), and top edge in CO₂ laser cutting are the main parameters in this study. Regression equations are obtained by doing an analysis of the experimental findings using statistical software to examine the impacts of process factors on surface conditions. Results show that the infill percentage and extruder temperature have an extraordinary effect on 3D-printed products' surface quality. 30% infill percentage and 190 °C extruder temperature result in the lowest surface quality with a value of 2.151 μm using DOE and RSM optimization. Also, the lowest value of the top edge is achieved at 275 μm with 300 W laser power and a 5 mm/s cutting speed. The proposed methods can be used to reduce material consumption in the product development.

Magnesium composites are next-generation lightweight materials for aerospace and military industries. However, the complex shape components of magnesium composites cannot be designed at ambient temperature, therefore, they need to be processed at elevated temperatures. Generally, material at elevated temperatures displays superplasticity. It is more interesting that magnesium composites exhibite high strain rate superplasticity compared to aluminum alloys. Therefore, this review article sheds light on the superplastic deformation behavior of magnesium composites fabricated by different routes. Further, the stress-energy, cavitation nucleation and its impact on the elongation to fracture have been explored. At the end of the review article, some terrifying unresolved subjects have been addressed, so that their potential use can be enhanced as complex shape components.

Free bending forming (FBF) is a flexible forming technology that gained significant attention recently because of its broad applications in critical industries such as the automotive, aerospace, and nuclear industries. Thus, this paper aims to present a comprehensive review of FBF technology and its flexibility in manufacturing thin-walled complex-shaped metallic tubes with variable curvatures. First, the historical development and state of the art of FBF technology were reviewed and discussed its importance in tube forming recently. Then, the fundamental principles, theoretical modelling, deformation mechanisms during complex bending, critical process parameters, and forming defects with a discussion of the recent research and technological developments of FBF technology under three-, five- and six-axis processes were explained. After that, the system dies and tools design of the FBF machines and the trajectory control of the bending die were presented. Afterwards, the mechanisms of manufacturing spiral and involute hollow metallic tubes and outstanding solutions for critical issues during tube manufacturing, such as springback, cross-section deformation, over-thinning (even cracking), and wrinkling instability were introduced. Finally, the paper is concluded by providing the discussions on the system, die and tool design methodology, and outlook of the FBF technology.

Conventional drilling has been widely used for making holes in structural materials. However, drawbacks like high cutting forces, poor surface finish, high cutting temperatures, excessive tool wear, and undesirable burr formation while drilling magnesium alloys have necessitated the development of alternative hole-making methods. Lately, the helical milling process has attracted interest in facilitating hole-making for assembly applications. However, the machinability of magnesium alloys using the helical milling process needs more investigation. Therefore, the presented work analyzed the influence of axial pitch, tangential feed, and spindle speed on cutting forces and surface integrity while milling AZ31 magnesium alloy. Axial feed was the most crucial factor contributing to the thrust force (71.8%), followed by tangential feed (13.2%). All three process variables impacted the radial force. Spindle speed was the most influential variable affecting the surface roughness (48.7%), followed by axial pitch (31.4%) and tangential feed (12.5%). Microhardness closer to the free surface of the hole was higher than the subsurface hardness. Moreover, microhardness showed an upward trend with the rise in axial pitch and tangential feed; however, it reduced with increased spindle speed.

Study on segregation, microstructure and mechanical properties of Al–6Si–3Cu–0.4Mg alloy was achieved by controlling the filling length in semisolid die casting. Results show that the microstructure is comprised of globular α–Al, eutectic Si, θ–Al₂Cu, Q–Al₅Cu₂Mg₈Si₆ and Fe–rich phase. After solution–ageing treatment, abundant θ–Al₂Cu and Q–Al₅Cu₂Mg₈Si₆ phases dissolve into the matrix. The liquid difference between the edge and middle area is 21.3% for 1/3 filling length, which is much higher than that of 15.0% for full filling length. As the filling length decreases, the increment of segregation degree at the bottom of the sample is detected. This segregation behavior leads to the strength and ductility both decreases from 425.0 MPa and 6.5% for 1/3 filling length to 405.3 MPa and 4.4% for full filling length, respectively. Besides, along with the formation of abundant fine θ–Al₂Cu phase and higher liquid fraction at the edge area, the ultimate tensile strength and elongation reaches 443.5 MPa and 5.2%. While in center area, the occurrence of coarsen θ–Al₂Cu phases leads to the tensile properties dramatically reducing to 378.7 MPa and 1.9%.

The ceaseless exploration for the improvement of ceramic materials has created a lot of techniques, all aimed at producing ceramic materials that can withstand environmental conditions and other factors. Most of thecommon techniques have their advantages and drawbacks. Some of the techniques involve the addition of a reinforcing phase to monolithic ceramic, the application of diverse sintering routes for the fabrication of ceramic products, and the preparatory methods for producing powder materials which cannot be jettisoned. These processes have been evaluated to influence the final ceramic products. Undoped/monolithic/single-phase ceramic has had some limitations in its processing, densification, and mechanical properties limiting its wide application in all circumstances. Hence, the incorporation of reinforcing phase, which can sometimes be called the secondary phase in the ceramic matrix, has significantly evolved into one of the possible means to nullify these challenges posed by undoped ceramics. This review consciously highlights and pinpoints all routes that have been taken to improve the properties of undoped SiC via the introduction of reinforcing phase, processing techniques, sintering techniques, etc. Finally, the possible prospects for future directions, advancement, and opportunities in the production of ceramic materials are concluded.

To improve the stretch-bend forming precision of aluminum alloy profiles with complex open sections, the relationship stress–strain distribution and the spring-back radius variation were analyzed under different stretch-bend stages. Numerical simulation was performed on the auxiliary mold stretch-bend and spring-back process for the L-section aluminum alloy profile with variable curvature. The effects of cover plate pressure and baffle gap on residual stress, section deformation and spring-back value after forming were investigated. The results show that the stretch-bend warpage can be avoided by setting the cover plate on the straight section of the profile web plate. With the increase of the cover plate pressure, the section distortion of the vertical plate increases by 82%, and the maximum spring-back increases by 71%. A baffle plate was added to the outside of the vertical plate, and the baffle gap is proportional to the amount of section distortion and inversely proportional to the spring-back value. The critical cover force (1 kN) and the critical baffle gap (1 mm) obtained by numerical analysis are used in the stretch-bend forming experiment, and the maximum error between the two results is 2.39%. The numerical simulation has a certain reference value for the rational design of the auxiliary mold stretch-bend process parameters.