Key Engineering Materials Vol. 1048

Abstract: This research explores the effect of elevated extrusion ram speed—achieved through die cooling with liquid nitrogen—on the mechanical behavior of 6060-aluminum alloy profiles. Mechanical characterization was conducted via tensile testing and nanoindentation, with the latter also employed to assess the alloy’s creep response. Results reveal that while the increased ram speed exerts minimal impact on Ultimate Tensile Strength (UTS) and Yield Tensile Strength (YTS), it notably enhances elongation. Furthermore, the study demonstrates a significant influence of ram speed on creep displacement as the dislocations generated by higher ram speeds seems to improve the creep resistance of the material. Keywords: 6060 Aluminum Alloy; Liquid Nitrogen Cooling; Nanoindentation; Tensile Testing; Creep Behavior.

Abstract: The growing use of extruded aluminum components in vehicle structures necessitates both strength and ductility to meet energy absorption requirements. In this study, a new compression calibration method for multi-chamber, hollow sections was developed with the aim of improving dimensional accuracy while enhancing the ductility of AA6061 extruded profiles. The influence of this method on mechanical properties was investigated through uniaxial tensile tests, three-point VDA bending tests, and axial crush tests. The uniaxial tensile test results revealed a reduction in the (logarithmic) strain at necking, while no significant changes were observed in yield and ultimate tensile strengths. On the other hand, the VDA tests showed a systematic increase in the normalized bending angle, indicating improved energy absorption characteristics. Visual inspection and the absorbed energy obtained by axial crush tests supported the findings in the VDA tests, indicating the compression calibration method enhances the crushability of extruded AA6061 profiles, although this improvement is not identified in standard tensile data. Overall, this work introduces a new, industrial calibration method for hollow extrusions that also enhances crushability.

Abstract: Friction Stir Extrusion (FSE), Direct Extrusion (DE) and Indirect Extrusion (IE) are all valid processes for the production of round profiles. However, differences and similarities between them have yet to be analyzed by the scientific community, since with the same geometry, each technology instills specific properties to the extruded product. In this context, the present work proposes an in-depth analysis via QForm UK Finite Element Method (FEM) software of the effect that each process has on a AA6061 extruded wire. Various combinations of rotational speed (200, 400, 600 rpm), feed rate (1, 2, 3, 4 mm/s) and pre-heating temperature (450, 500°C) were analyzed to assess differences and similarities between FSE, DE and IE. The feedstock material for FSE was chosen to be powder, while a solid billet was used for conventional extrusion.

Abstract: This study investigates an adaptive die concept for cold extrusion that actively modulates radial preload during the main forming and ejection phases. A Gaussian process regression (GPR) surrogate, trained on fewer than 400 finite-element simulations, provides a highly data-efficient model capable of accurately predicting geometric tolerances, residual stresses, and process forces. Experimental spot measurements validate the physical trends captured by the surrogate, demonstrating reliable reproduction of the underlying mechanical interactions. The results show that increased preload during forming enables micrometer-level calibration of final diameters, while higher preload during ejection promotes beneficial compressive residual stresses at the cost of elevated ejector forces. A part-to-part control strategy effectively improves accuracy by independently steering two target properties through separate preload adjustments. Furthermore, a reinforcement learning-based controller, enhanced by flow stress estimates derived from hardness measurements, reduces variance and compensates for stochastic fluctuations in material and friction conditions. Overall, the adaptive die system, combined with surrogate-and RL-based control provides a robust foundation for achieving high dimensional precision and stable product properties under future variability scenarios, such as green steel and sustainable lubrication systems.

Abstract: The transition towards sustainable mobility demands lightweight and modular carrier systems for high-voltage batteries and fuel cells that combine structural efficiency with effective thermal management. This study examines the feasibility of producing thin-walled, large-scale aluminum extrusion profiles for modular battery housings using AA6063. Numerical simulations and experimental trials are conducted to optimize die design and define process limits along the relation between circumscribing circle diameter (CCD) and minimal wall thickness t_min. Furthermore, different quenching methods are used to investigate the influence on surface distortion and final mechanical properties. A streamlined die design with reduced mandrel deflection has enabled defect-free extrusion under controlled conditions for the extrusion of a thin-walled, large-scale profile with a CCD-to-t_min ratio of 138. A narrow process window is identified for extrusion of defect-free profiles. Quenching studies have shown that active cooling methods affect surface deformation but have negligible influence on mechanical properties or microstructure due to efficient heat extraction inherent to thin-wall geometries for the investigated alloy. Scaling experiments using an enlarged cross section by a factor of 2.5 have confirmed similar process stability without wall thickness adjustments, achieving up to 38 % weight reduction compared with conventional designs under industrial conditions.

Abstract: Forming processes significantly influence the product properties of a formed workpiece. Next to the effects of work hardening and residual stresses, the influence of ductile damage determines the final performance of a formed component. Thus, precise damage models are crucial for designing new forming process sequences. In general, this is achieved by modelling the evolution of damage as a function of hydrostatic and deviatoric stress, characterized by the stress triaxiality and the Lode-parameter. However, calibrating damage models to the effects of triaxiality and the Lode-parameter is not trivial, since experiments usually represent a combination of both influences. A recent experimental approach by the authors offers the possibility to vary the Lode-parameter in extrusion experiments while keeping the triaxiality constant. This paper aims to use this data of the isolated deviatoric effect on damage to calibrate a damage evolution equation. The model is calibrated to void area fraction measurements obtained by scanning electron microscopy of extruded case-hardening steel 16MnCrS5. For validation, the model predictions for non-constant Lode-parameter histories are compared to corresponding experiments. The model and experiments are in good agreement.

Abstract: Aluminum 7000 series alloys are widely used for aerospace and transportation applications due to their high strength-to-weight ratio. This research investigates the impact of zinc (Zn) and magnesium (Mg) content on the hot extrudability and tribological behavior. Elemental quantities straight away impact flow stress, determining the manufacturing parameters, whereas galling and adhesion frequently degrade tool life. This work illustrates that by assessing essential ram speeds and temperature limits, adjusting Zn and Mg concentrations considerably improves the extrudability limit. A decreasing flow stress during deformation reduces micro-cracking tendency and improves surface quality. The findings provide critical compositional guidelines for high-strength aluminum alloys, effectively balancing processing efficiency with improved surface quality and reduced element adhesion behavior, ensuring better industrial outcomes for advanced structural components.

Abstract: Abstract. Tubes with non-uniform thickness are needed to even out wall thickness in draw bending and provide higher stiffness in specific directions in some applications. Tailored local heating of the tubes in tube sinking operations should reduce the local flow stresses and facilitate differential deformation along the circumference of tubes to form tubes with uneven wall thicknesses. Local heating of tubes prior to entry into the die in tube sinking is implemented in this research to form tubes with higher thickness in desired directions. Initial experiments are conducted using plasma heating by tungsten inert gas (TIG) welding equipment on EN AW 6060 AlMgSi0.5 aluminum tubes. The process window is described by varying the process temperature (weld current between 50 A and 80 A) while altering the degree of deformation, the tube diameter, and tube thickness. Tubes with no defects were formed at 50 A. Increasing the weld current led to a higher wall thickness (up to 25% thickness increase), however, high weld currents also favored the formation of surface defects, wrinkle formation, or burn-through holes depending on the process setup. The process window was larger for tubes with higher wall thickness.

Abstract: Transverse (charge) welds form during billet transitions in aluminium extrusion when incoming material progressively replaces residual metal inside the die, defining the length of extrudate that must be scrapped. This study aimed to quantify charge weld evolution under industrially relevant conditions that are often underestimated in scrap length assessment, including multi-cavity flow imbalance, non-symmetric multi-profile placement, and billet-to-billet thermal stabilisation effects. Three case studies were analysed using finite element simulation in QForm UK: (i) the International Extrusion Benchmark 2023 multicavity die producing three hollow tubes with intentionally varied port and bearing designs, (ii) an industrial two-profile die with translated (non-mirrored) profile positioning to avoid post-extrusion rotation, and (iii) a complex industrial profile extruded over multiple consecutive billets. The benchmark study demonstrated strong agreement between simulation and experimental charge weld evolution for two profiles, supporting the reliability of the predicted cavity-dependent differences driven by port volume. In the translated two-profile configuration, the charge weld cut length required for full purity increased from 1674 mm to 1940 mm (+16.0%), and by +15.9% under the 95% industrial criterion (1458.1 mm vs 1690.7 mm). Billet-to-billet variability was substantial, with charge weld length increasing by +70.1% from the first to the fifth billet (2819.0 mm to 4791.7 mm), before stabilising. Overall, the results show that charge weld length is governed by residence-time differences through ports and flow channels, requiring profile-specific assessment and consideration of process stabilisation. In this context, FE simulation provides an effective means to localise the mixed zone and to support die optimisation strategies aimed at reducing scrap.