Search Results (868)

The continuous joining of aluminum alloys to engineering thermoplastics has emerged as a promising manufacturing path for lightweight hybrid structures, yet the influence of polymers’ mechanical behavior on friction stir joining remains poorly understood. This work investigates the role of melt rheology on the morphology, joining interface, and mechanical strength of dissimilar joints that combine AA6082-T6 with two engineering-grade thermoplastics, Noryl^® GFN2 and SustaPEEK^®. Two joining strategies were assessed under identical processing conditions: conventional friction stir joining (FSJ) and through-slot friction stir joining (TS-FSJ), the latter incorporating thin titanium strips intended to reduce heat transfer to the polymer. Joint morphology was assessed by optical and scanning electron microscopy, mechanical performance was evaluated through quasi-static tensile-shear testing, and the rheological behavior of both polymers was characterized by steady shear and oscillatory measurements. Conventional FSJ produced defect-free aluminum–Noryl joints, with a mechanical strength of 111.3 ± 8.4 kN/m, whereas aluminum–PEEK joints exhibited localized polymer overflow, poor surface finish and scattered strength performance of 116.7 ± 77.2 kN/m. Rheological measurements showed that PEEK exhibited higher melt viscosity and viscoelastic moduli, restricting polymer flow and promoting unstable interface formation. Although titanium inserts reduced heat transfer in TS-FSJ, their deformation reduced the effective joining area, resulting in lower tensile strength. Polymer rheology was identified as one of the key factors governing material flow, defect formation, process stability, and the joints’ mechanical performance, emphasizing the importance of tailoring the processing parameters reflecting the rheological characteristics of each polymeric base material. Full article

Continuous bending under tension (CBT), also known as cyclic bending under tension, is an experimental deformation technique capable of achieving large plastic strains under relatively low tensile loads. However, the broader application of CBT testing remains dependent on the availability of dedicated experimental setups and the suitable adaptation of conventional mechanical testing systems. This study presents the design and development of a CBT testing device intended for integration with conventional universal testing machines. The proposed system consists of four main subsystems: specimen grips, a roller train, a motor system, and a supporting structure. The developed device was experimentally assessed using DP600 advanced high-strength steel and AA6022-T4 aluminum alloy sheets with nominal thicknesses of 1.5 and 2.0 mm, respectively, under selected CBT operating conditions. The system successfully performed CBT tests, enabling the acquisition of force–elongation responses, cycles to fracture, and post-test specimen observations. The experimental results reproduced the characteristic CBT response, showing significantly higher total elongation compared with uniaxial tensile testing while requiring substantially lower tensile forces. The developed device demonstrated operational and mechanical stability, providing a practical platform for laboratory-scale investigations of sheet metal deformation behavior under CBT loading conditions. Full article

This study investigates the influence of joining technology on the microstructural evolution and mechanical properties of joints produced from extruded AA2017 aluminum alloy rods. Rotary Friction Welding (RFW) was compared with conventional TIG welding to evaluate the effects of solid-state and fusion-based joining mechanisms. The joints were characterized using scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), electron backscatter diffraction (EBSD), hardness measurements, tensile testing, and fracture analysis. TIG welding produced a coarse-grained cast microstructure within the fusion zone, whereas RFW generated a fine-grained microstructure formed through intense thermomechanical deformation accompanied by crystallographic texture evolution. These distinct microstructural characteristics resulted in markedly different mechanical behavior. The RFW joints achieved an ultimate tensile strength of 247 MPa and an elongation to failure of 12.5%, compared with 160 MPa and 1.7%, respectively, for the TIG-welded joints. The results demonstrate that the joint formation mechanism is the primary factor governing the microstructural evolution and mechanical performance of AA2017 alloy joints. Full article

The increasing demand for lightweight and corrosion-resistant structures has accelerated the use of AA5083 aluminium alloy in automotive, aerospace, marine and transportation industries owing to its excellent corrosion resistance, weldability and favourable strength-to-weight ratio. However, the fabrication of complex AA5083 components remains challenging because of limited formability, localised thinning, fracture and springback associated with conventional forming processes. Robotic incremental sheet forming (RISF) has emerged as a promising dieless manufacturing technology capable of producing complex and customised components with reduced tooling requirements. Recent developments in assisted RISF, particularly heating-assisted and hydro-assisted approaches, have further enhanced process capability. The reviewed literature consistently demonstrates that heating-assisted RISF improves formability by reducing flow stress and fracture tendency, whereas hydro-assisted RISF provides superior thickness distribution, deformation stability and dimensional accuracy. Despite these advances, significant challenges remain, including the lack of standardised processing conditions, limited comparative studies between cold and assisted RISF, insufficient understanding of hydro-assisted RISF for AA5083, and the absence of comprehensive process–structure–performance correlations. This review critically summarises the principles of ISF, RISF and assisted RISF technologies, evaluates their technical developments, industrial potential and economic considerations, and identifies the major research gaps limiting industrial implementation. Future research should focus on standardised processing methodologies, predictive modelling, integrated process optimisation and comprehensive material characterisation to facilitate the wider adoption of assisted RISF for manufacturing advanced lightweight AA5083 components. Full article

The paper is the first to highlight what appears to be a unique and unusual failure mechanism that is associated with cracks that nucleated from corrosion pits in aluminium alloy (AA) 7085-T7452 specimens that were tested under a variable amplitude load spectrum. In this study, cracks initially nucleated at corrosion pits and first grew as would be expected, namely at ninety degrees to the surface and perpendicular to the applied load. However, after reaching a depth of approximately 2 mm, these various Mode I cracks transformed into what can be best described as interlayer cracks with their surfaces at an angle of approximately ninety degrees to the initial fatigue crack surface. Analysis of the failures revealed that the maximum value of the stress intensity factor at which this phenomenon occurred, which we have defined as K_IL, was substantially less than the fracture toughness for this material. As such, failure was not due to classical Mode I failure, but rather due to K exceeding what we will term K_IL. Despite the unusual failures, it was found that, up to the point where this phenomenon occurred, the crack growth versus cycles histories could be reasonably accurately predicted using the small crack growth equation developed by the authors in a prior study on AA 7085-T7452 specimens with a fastener hole. Full article

This paper investigates the microstructural evolution and mechanical performance of dissimilar friction stir-welded (FSW) T-joints produced from AA5083-H111 and AA7020-T651 aluminium alloys. The study focuses on the effects of tool rotational speed, traverse speed, and tool pin length on joint quality and mechanical strength. Welding experiments were conducted at two rotational speeds (400 and 700 rpm) and three traverse speeds (50, 100, and 200 mm/min) using two Triflute tools with pin lengths of 4.8 mm and 6.8 mm. The welded joints were examined by macro- and microstructural observations, microhardness measurements, and bending tests performed under pull-out loading conditions. The results showed that the use of the longer pin significantly improved material mixing and reduced the extent of internal defects, resulting in higher bending strength. Increasing the traverse speed improved the mechanical performance, whereas an excessively high rotational speed reduced joint strength due to increased heat input and unfavourable microstructural changes. Microhardness profiles showed no reduction in hardness within the heat-affected zones relative to the base materials and indicated localised hardening in the stir zone. For the investigated material configuration and tool geometries, the highest joint strength was obtained at a rotational speed of 400 rpm and a traverse speed of 200 mm/min using the longer-pin tool. The study confirms the critical role of process parameter optimisation and tool geometry in producing high-quality dissimilar FSW T-joints suitable for lightweight structural applications. Full article

AA6061-T6 undergoes work hardening, dynamic recovery, and progressive flow softening during hot torsion, yet a systematic single-campaign dataset with quantified experimental uncertainty is absent from the literature. Gleeble hot torsion tests were conducted at eleven conditions from 250 to 450 °C and 0.91 to 9.07 s⁻¹. With the stress multiplier fixed a priori at α = 0.045 MPa⁻¹ from compression literature on this alloy, a two-stage calibration determined the remaining Garofalo–Arrhenius constants: the temperature-slope stage anchors Q = 151.1 kJ mol⁻¹ (consistent with Al lattice self-diffusion), and a global Zener–Hollomon regression conditional on Q yields n = 1.371 and A = 3.51 × 10¹⁰ s⁻¹; a fully simultaneous three-parameter fit is shown to be practically unidentifiable on the three-level matrix. Training AARE = 15.5% (R = 0.908); leave-one-out cross-validation gives AARE = 23.0%, bounding the predictive uncertainty. The Prasad instability map identifies 400–450 °C at 0.91–2.72 s⁻¹ as the optimal hot-forming window; flow instability is predicted at 350 °C (outright at 2.72 and 9.07 s⁻¹, with the 0.91 s⁻¹ condition at the map boundary), and macroscopic fracture was observed in all three specimens tested there. Optical microscopy in specimen T1 (ε_eq = 3.69) shows elongated subgrains at the gauge center and fine-grained zones near the fracture surface consistent with localized geometric dynamic recrystallization. The activation energy, smooth post-peak softening, and subgrain wall morphology identify dynamic recovery as the likely dominant restoration mechanism. Adiabatic heating and a 24% peak-stress repeatability scatter at the single repeated condition (450 °C, 9.07 s⁻¹) are quantified and propagated into the constitutive model uncertainty bounds. Because the training-to-cross-validation error gap (15.5% versus 23.0% AARE) reflects the limited three-level strain-rate matrix, the calibrated equation is recommended for interpolation within the tested window of 300 to 450 °C and 0.91 to 9.07 s⁻¹ (noting that 300 °C was tested only at 0.91 s⁻¹, so higher-rate predictions at that temperature are extrapolations) and for forming-window identification, not for extrapolation beyond this domain without additional validation data. Full article

In this study, isothermal annealing of AA8014 aluminum alloy burst vents was performed at 250–500 °C for 10 s to 2 h, and Johnson–Mehl–Avrami–Kolmogorov (JMAK) kinetic analysis was employed to determine the recrystallization parameters at 300 °C. An Avrami exponent of n = 1.87 and an apparent activation energy of Q = 156 kJ/mol were obtained, revealing a recrystallization mechanism driven by high stored energy and synergistically regulated by particle-stimulated nucleation at coarse second-phase particles and Zener pinning by fine Al(Fe,Mn)Si dispersoids. The burst pressure evolution was highly temperature-dependent: annealing at or below 300 °C led to sluggish recrystallization and a gradual pressure decline, whereas annealing at 350 °C and above resulted in recrystallization completion within 10 s and a sharp pressure drop to a stable plateau of approximately 0.92 MPa. The Al(Fe,Mn)Si dispersoids showed no significant differences in size distribution or grain-boundary pinning after 1 h at both 300 °C and 500 °C. This invariance across the tested range rendered the microstructure and burst performance insensitive to process variations. A quantitative predictive model correlating the recrystallized fraction with the burst pressure was established, with prediction errors less than 4.1%. The 300–350 °C interval is identified as the critical temperature window for regulating recrystallization kinetics and burst pressure, providing a rational basis for the heat-treatment design of burst vents. Full article

In this study, AA7068 aluminum matrix composites reinforced with TiB₂/TiC were fabricated via mechanical alloying and microwave sintering to investigate the influence of reinforcement content and sintering temperature on microstructure, mechanical properties, and dry sliding wear. Mechanical alloying refined powders, reducing D₅₀ from 51.5 µm (AA) to 22.5 µm (AC9) and enhancing dispersion and retention of TiB₂/TiC particles. XRD confirmed α-Al as the dominant matrix phase, preserved TiB₂ and TiC phases, and limited MgAl₂O₄/ZnAl₂O₄ spinel formation. Crystallite refinement and increased lattice microstrain were observed with the addition of reinforcement. Microhardness increased with reinforcement content and sintering temperature, reaching 122.2 HV_0.05 in AC9-2. At the same time, the highest compressive strength was observed in AC6-2 (431.05 MPa), indicating that optimal load-bearing depends on densification and interfacial integrity rather than hardness alone. AC9-2 exhibited the best wear resistance, with a cumulative specific wear rate of 2.723 × 10⁻⁴ mm³/Nm over 1000 m. SEM-EDS analysis revealed oxide-rich tribolayers, mechanically mixed layers, TiB₂/TiC fragments, and Fe-rich third-body debris, indicating wear is predominantly hardness-controlled but strongly influenced by microstructural factors. Overall, TiB₂/TiC hybrid reinforcement improves AA7068 wear resistance through combined hard-particle load-bearing, reduced penetration, tribolayer stability, and third-body effects, offering insight for high-performance hybrid aluminum composites. Full article

The effects of accumulative roll bonding (ARB) on the microstructure and mechanical properties of an AA 1060/Y₂O₃ nanocomposite are investigated. AA 1060 alloy sheets that had been pre-rolled to a thickness of 1 mm were annealed at 430 °C, stacked with Y₂O₃ nanoparticles, and roll-bonded with a 50% thickness reduction per pass up to five passes. FESEM images, tensile testing (ASTM E8), and Vickers hardness measurements were used to characterize the material. With an increasing number of ARB passes, the dispersion of the Y₂O₃ particles within the AA 1060 sheets improved, as indicated by the increasing value of the dispersion index D (from 0.35 at pass 1 to 0.81 at pass 5); the ultimate tensile strength of the nanocomposite sheets increased from 77.5 MPa for the as-annealed sheets to 187 MPa for the sheets after five passes of roll bonding, and the hardness of the sheets reached 57.5 HV after five passes of roll bonding (≈2.4× the hardness of the annealed sheets). Furthermore, the elongation of the nanocomposite sheets decreased sharply after the first pass of roll bonding but then stabilized between 3.5 and 5%. A physics-guided saturation model is fitted to the measured UTS data, and leave-one-out cross-validation is used to assess its limited predictive capability. Full article

This study investigates the effect of Gas Metal Arc Welding (GMAW) parameters on solidification cracking and mechanical behavior of AA6061 and AA7075 aluminum alloys, which are widely used in automotive, aerospace, and battery-related applications due to their low density, corrosion resistance, and high specific strength. The influence of filler metals, ER4043 and ER5356, welding speed, wire feed speed, and calculated heat input was evaluated using the Circular Patch Test (CPT). Surface and internal cracking were examined by X-ray inspection, while microstructural evolution, phase formation, hardness, tensile behavior, and local strain distribution were analyzed using optical microscopy, SEM/EDS, XRD, microhardness testing, micro-tensile testing, and Digital Image Correlation (DIC). The results show that cracking susceptibility depends on the combined effects of welding speed, heat input, filler-metal chemistry, and dilution. The observed cracking behavior is associated with local compositional variations, weld defects, and the formation of low-melting/eutectic or secondary constituents within the fusion zone, rather than being attributed to a single factor. ER5356 showed favorable cracking resistance for AA7075 under the selected conditions, while ER4043 generally improved cracking resistance for AA6061. The mechanical response and fracture behavior were also influenced by filler composition and local weld microstructure. These findings provide useful guidance for selecting welding parameters and filler metals to improve weld quality and reduce solidification cracking in AA6061 and AA7075 aluminum alloys. Full article

Accurate prediction of surface roughness and cutting forces in milling aluminum alloys remains challenging under data-scarce conditions, where limited experimental data restricts the application of conventional machine learning models. This study addresses this gap by developing a systematic machine learning framework using 108 milling experiments (repeated to 216 tests) on aluminum alloys AA2024-T351 and AA6061-T6. Five primary machining inputs—material type, spindle speed, feed rate, depth of cut, and tool coating—were used. Through feature engineering, 35 interaction features were generated to capture non-linear relationships. A two-step preprocessing strategy was applied: Winsorization at the 5th and 95th percentiles to handle outliers, followed by hybrid scaling combining RobustScaler and MinMaxScaler. Eight machine learning algorithms, including XGBoost, NGBoost, LightGBM, CatBoost, Random Forest, MLP, SVR, and Least Squares Boosting, were developed and hyperparameter-optimized using the Optuna framework with Tree-structured Parzen Estimator. Models were evaluated using R², MAE, and RMSE on a 70/15/15 train–validation–test split. Results demonstrate that XGBoost achieved the highest predictive accuracy for surface roughness (Ra) (R² = 0.99829) and for resultant cutting force (FN) (R² = 0.997). Feed rate was identified as the dominant machining parameter, accounting for 87.7% of the total importance in predicting surface roughness. SHAP analysis confirmed that engineered interaction features—particularly Feed_Coating and Material_Feed—carry strong physical relevance. Additionally, NGBoost enabled probabilistic regression, providing uncertainty estimates. The proposed framework proves highly effective for multi-output prediction in machining under limited data, offering a robust, interpretable, and industry-ready solution for quality control in aluminum alloy milling operations. Full article

Chromate-free conversion coatings are increasingly investigated as environmentally acceptable alternatives to conventional chromate conversion coatings for corrosion protection of aluminum alloys. In the present study, the electrochemical behaviour and long-term corrosion stability of several commercial conversion coating systems based on trivalent chromium (TCP), zirconium (ZrCC) and zirconium/titanium (Zr/TiCC) were systematically evaluated on AA3003 aluminum alloy and compared to chromate conversion coating (CCC) CR614. Three TCP coatings (ST650, MC1300 and B30002), two ZrCC (MC1700 and MC160/161), and one Zr/TiCC (B2040) were investigated. Coatings were prepared at pre-selected pH and concentration, but at varying conversion times. The protective performance of the coating was then tested across various exposure conditions using potentiodynamic polarization measurements: (i) after 24 h of exposure to air, (ii) after 24 h of immersion in 3.5 wt.% NaCl solution and (iii) simulated acid rain solution, and (iv) after exposure in a salt spray chamber for 500 h. The protective performance strongly depended on both the conversion conditions and the exposure environment. The optimal conversion times ranged between 40 s and 18 min, depending on the coating type. Differences between the investigated systems remained relatively limited when investigated after exposure to air and immersion in the simulated acid rain solution. However, in chloride-containing environments, substantially greater differentiation between the coatings was observed. Among the investigated systems, TCP coatings exhibited the most favourable overall corrosion performance, particularly after prolonged salt spray exposure, where ST650 and B30002 polarization resistance values were approximately 8800 and 5300 kΩ cm², respectively, together with corrosion current densities as low as 0.0004 and 0.001 μA cm⁻². ZrCC systems MC1700 and MC160/161 also provided significant corrosion protection, achieving polarization resistance values around 2700 and 2400 kΩ cm² after 500 h of salt spray exposure, whereas the Zr/TiCC coating B2040 exhibited poorer long-term performance. The results further demonstrated that prolonged salt spray exposure provides considerably more realistic evaluation of long-term coating protectiveness than short-term electrochemical measurements alone. Overall, optimized TCP and ZrCC systems provided corrosion protection under chloride-containing conditions comparable to or superior to the investigated conventional chromate conversion coating CR614 deposited on AA3003 alloy. Full article

The development of lightweight aluminum matrix composites with improved mechanical performance and thermal stability using sustainable reinforcement materials remains a significant challenge in structural materials engineering. Although ceramic-reinforced aluminum composites exhibit enhanced strength and thermal resistance, the potential of bio-derived snail shell particles as environmentally sustainable reinforcements remains insufficiently explored. In this study, snail-shell-reinforced AA6061 aluminum matrix composites were fabricated by stir casting to investigate their microstructural characteristics, mechanical behavior, phase composition, and thermal stability. Snail shell particles, predominantly composed of CaCO₃, were processed to particle sizes of 50–75 µm before incorporation into the molten aluminum matrix. Characterization was performed using scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), tensile and hardness testing, thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The results revealed relatively uniform particle dispersion and satisfactory matrix–reinforcement interfacial compatibility. The tensile strength increased from 155 ± 5 MPa for the unreinforced alloy to 211 ± 4.8 MPa for the reinforced composite, corresponding to an improvement of approximately 36%, while elongation increased from 2.4 ± 0.2% to 4.6 ± 0.4% (92%). XRD analysis confirmed the presence of Al, CaCO₃, Mg₂Si, and minor CaO phases, indicating successful reinforcement incorporation and strengthening phase formation. Thermal analysis demonstrated enhanced thermal stability, increased residual mass retention, and improved resistance to thermal degradation. This work demonstrates that bio-derived snail shell particles are viable and environmentally sustainable reinforcements for lightweight aluminum matrix composites intended for structural engineering applications. Full article

Laser powder bed fusion (LPBF) of high-strength aluminum alloy 7075 (AA7075) is severely limited by hot cracking. However, the underlying mechanisms, particularly the coupling between thermal fields, solidification microstructure, and cracking behavior, remain insufficiently clarified. This study elucidates these mechanisms by integrating experimental characterization with thermal simulation to investigate the temperature field, microstructure, and cracking relationships in both AA7075 and a crack-resistant 7075-Er-Zr alloy. Results show that coarse hot crack morphology is highly dependent on linear energy density E_L. In AA7075, E_L < 450 J/m promotes laterally inclined cracks (short, narrow cracks extending from the melt pool boundary toward the track center), whereas E_L higher than that value leads to the continuous centerline cracks (long, wide cracks along the track center). Fine microcracks are also observed at melt pool boundaries. The 7075-Er-Zr alloy demonstrates superior crack resistance. At E_L = 600 J/m, longitudinal centerline cracks still penetrate along the track, but the alloy achieves crack-free tracks at 200 W with scanning speeds above 1000 mm/s, otherwise exhibiting only short discontinuous cracks. Microcracks at melt pool boundaries are markedly suppressed in the modified alloy. The enhanced crack resistance is attributed to Er/Zr-induced grain refinement and a transition to an equiaxed grain structure, which disrupts intergranular gaps. Critically, thermal simulations identify an annular region with a peak temperature gradient. In AA7075, this region develops aligned columnar grains that facilitate both microcracks and centerline cracks. In the 7075-Er-Zr alloy, microcracks are fully eliminated within this region. However, a residual crystallographic texture persists in the annular region, which promotes the continued occurrence of centerline cracks under high energy density (e.g., E_L = 600 J/m). The annular region remains a critical weak link, and its microstructural control determines the prevailing crack type. This work provides a fundamental understanding of the thermal-microstructural origins of cracking and offers a theoretical foundation for developing crack-resistant aluminum alloys via LPBF. Full article