Acta Polytechnica https://doi.org/10.14311/AP.2025.65.0349 Acta Polytechnica 65(3):349–360, 2025 © 2025 The Author(s). Licensed under a CC-BY 4.0 licence Published by the Czech Technical University in Prague IMPACT OF PROCESS PARAMETERS ON THE MECHANICAL AND SURFACE PROPERTIES OF AA6082 Bilgehan Tuncaa,∗, Bahadır Karacab a Sistem Alüminyum, Department of R&D Center, Tekirdağ, Turkey b Zahit Alüminyum, Department of R&D Center, Adana, Turkey ∗ corresponding author: bilgehantnca@gmail.com Abstract. This study investigates the effects of chemical composition, heat treatment, and processing parameters on the mechanical properties, microstructure, and surface quality of AA6082 aluminium alloy. Three castings with varying Mg and Si content were subjected to homogenisation at 580 °C for 8 and 10 hours, followed by extrusion and artificial ageing at 180 °C for 6, 8, and 10 hours, yielding 18 samples. Tensile testing, microstructural analysis, SEM examination, and anodic oxidation (18 V, 26–32 minutes) were conducted to assess performance. Results revealed that the highest tensile strength (361 MPa) and yield strength (332 MPa) were achieved with 8-hour homogenisation and ageing (B2 sample), attributed to optimal β′′ precipitate formation, finer grain sizes, and a favourable composition (Mg: 0.92 %, Si: 1.09 %). The surface quality and hardness were enhanced by water shock and nitrogen gas cooling during extrusion, while the 10-hour homogenisation reduced porosity but increased the risk of over- ageing. SEM analysis confirmed ductile fracture in high-strength samples, and anodising produced thicker (11.7 µm), glossier coatings with longer processing times. These findings highlight the critical interplay of heat treatment duration, cooling strategies, and surface finishing in optimising AA6082 for industrial applications, with implications for process design and alloy development. Keywords: Aluminium alloy, AA6082, heat treatment, aluminium casting, extrusion. 1. Introduction The use of aluminium alloys is increasingly prevalent across various application areas due to their excel- lent physical and mechanical properties. Additionally, aluminium alloys, which are distinguished by their varying chemical compositions, are preferred in indus- trial applications for their superior machinability [1]. The improvement of their machinability and perfor- mance, tailored to specific application domains, has been extensively investigated within the framework of material improvement and development [2]. A criti- cal aspect of the aluminium alloy production process involves determining the appropriate chemical compo- sition based on the alloy specifications. Furthermore, heat treatment, conducted at varying temperatures and durations, plays an essential role in achieving a homogeneous microstructure. This heat treatment process directly influences extrusion capabilities and contributes to enhancing the mechanical properties of extruded aluminium profiles [3]. The 6XXX aluminium alloy series, defined as the Al-Mg-Si system, exhibits high fabricability. The chemical and microstructural composition of these alloys significantly impacts their functional properties and application suitability. Research has indicated that the mechanical properties of 6XXX-series alu- minium alloys, subjected to heat treatment with T6 tempers, are strongly dependent on both the chemical composition and the ageing duration. In addition, the formation of β′′ precipitates, which are closely linked to the hardness of aluminium alloys, increases with higher Mg and Si content in the alloy’s chemical com- position [4]. Numerous studies have focused on the effects of heat treatment and casting parameters on the mechanical and microstructural properties of alu- minium alloys. It has been reported that intermetallic phases, such as Al-Fe, Al-Fe-Si, and Al-Fe-Mn-Si, with varying morphologies and physical properties, form depending on the casting conditions such as cooling rate and the alloy’s chemical composition. Moreover, β-Mg2Si phase precipitates, which are responsible for the strength of aluminium alloys, develop during cool- ing following the homogenisation [5]. Prabhukhot and Prasad (2015) [6] investigated the effect of heat treatment on the hardness of AA6082-T6 aluminium alloy. Artificial ageing was conducted at 175–220 °C for 2–10 hours, with some samples pre- treated with solution heat treatment at 500 °C. Hard- ness was measured on the Rockwell E scale. Results showed that both processes altered the grain structure, reducing hardness, with brittle Mg2Si phase increasing notably above 200 °C. Ma et al. (2015) [7] examined the effect of solution heat treatment (SHT) on the mechanical properties and fracture behaviour of AA6082 aluminium alloy sheets. Using a central composite design, specimens underwent SHT at 440–575 °C for 1.7–58 minutes, followed by water quenching and artificial ageing at 190 °C for 3 hours. Tensile tests revealed that ulti- mate tensile strength (UTS) increased and ductility de- creased with higher SHT temperatures and time. Re- 349 https://doi.org/10.14311/AP.2025.65.0349 https://creativecommons.org/licenses/by/4.0/ https://www.cvut.cz/en Bilgehan Tunca, Bahadır Karaca Acta Polytechnica sponse surface models were developed, and the NSGA- II algorithm optimised these parameters, showing UTS and ductility ranging between 201–252 MPa and 32–30 %, respectively, at 510–534 °C and 12–28 min- utes. Scanning electron microscopy analysis indicated ductile fracture, with dimples becoming shallower as the SHT temperature and time increased. Meredith et al. (2002) [8] investigated the inter- metallic phase selection during the solidification of Al-Fe-Si(-Mg) alloys, focusing on 1XXX and 6XXX series compositions. Using directional solidification (20–120 mm min−1) and varying Si (0.1–0.9 wt %) and Mg (0–3.5 wt %) content, they analysed phase transi- tions via microscopy, X-ray diffraction, and thermo- dynamic modelling. Results showed that increasing Si shifted phases from binary Al-Fe (e.g. Al6Fe) to ternary Al-Fe-Si (e.g. α-AlFeSi, β-AlFeSi), while Mg (> 1.0 wt %) favoured AlmFe and altered the primary aluminium morphology from columnar to dendritic, mirroring grain refiner (Al-Ti-B) effects. These shifts were linked to thermodynamic stability and kinetic factors, such as solidification velocity and primary phase morphology. The formation of these intermetallic phases based on Fe content is directly affected by the cooling rate and the Fe to Si ratio in the matrix [9]. The Al-Mg responsible for precipitation hardening can be signifi- cantly improved by rapid solidification after the plastic deformation process. The hot extrusion process can be combined with rapid solidification for obtaining an aluminium profile with high mechanical proper- ties [10]. The extrusion process, recognised as a form of plastic deformation, enables the transformation of an aluminium billet’s dimensions under conditions of high temperature and high pressure. In this process, parameters, such as die temperature (°C), extrusion speed (mm s−1), press pressure (bar), and press du- ration (s), are critical and significantly influence the extrusion performance of high-strength aluminium alloys. These parameters directly govern the alloy’s shaping process and the mechanical properties of the final product. Precise adjustment of these factors is es- sential for aluminium alloy types containing different primary elements, as each alloy exhibits unique chem- ical compositions, flow characteristics, and melting behaviour [11]. The plastic deformation technique reveals that alu- minium alloy groups with different chemical compo- sitions exhibit distinct metal flow behaviour. For in- stance, an increase in extrusion temperature improves the alloy’s fluidity and facilitating shaping, however, excessively high temperatures can lead to surface de- fects (e.g. hot cracking) or undesirable grain growth in the microstructure. Conversely, if the tempera- ture is not high enough, the material loses fluidity, resulting in increased press pressure and potential die wear. On the one hand, raising the die temper- ature can reduce friction between the material and the die, yielding a smoother surface, however, if this temperature becomes excessive, the dimensional accu- racy of the profile can be compromised. On the other hand, a decrease in die temperature hinders the flow and heightens the risk of surface scratches or shape irregularities. When extrusion speed (mm s−1) is increased, pro- duction pace may accelerate, however, excessively high speeds can cause inconsistencies in the flow and the development of internal stresses. If the speed is too low, the process duration extends, reducing energy efficiency. Elevating press pressure (bar) facilitates the shaping of harder alloys, however, this can im- pose excessive strain on the die, shortening its service life. The press duration (s) must align with other parameters; if too brief, shaping may remain incom- plete, while if overly prolonged, it risks energy waste and material fatigue. Moreover, one of the key con- siderations is the precise control of material flow in high-strength aluminium alloys during extrusion, as this fundamentally determines both product quality and process effectiveness [12]. 2. Material and methods In this study, three different castings of the AA6082 al- loy were performed. Subsequently, these three castings were subjected to homogenisation annealing processes at a constant temperature of 580 °C for 8 and 10 hours. As a result of these processes, six different samples were obtained. The samples were then put through an extrusion process to produce aluminium profiles. Afterwards, for the artificial ageing process, the pro- files were kept in an environment with a constant temperature of 180 °C for three different durations: 6, 8, and 10 hours. Subsequently, the profiles under- went an anodising process for anodic oxidation coating. Throughout this process, a total of eighteen samples were produced. To examine the differences in the homogenisation process after casting, microstructure analyses were conducted on the billets. Following the artificial ageing process, tensile test samples from the profiles were analysed to investigate the differences. Finally, SEM analyses were performed to examine the coating following the anodic oxidation process. 2.1. Billet casting process It has been reported that the chemical composition of a casting alloy and the casting parameters play a critical role in the formation of intermetallic phases within an aluminium matrix [8]. The casting process for the AA6082 aluminium alloy was carried out in induction furnaces. The chemical composition was analysed using a spectrometer. Aluminium billets with a diameter of 127 cm and a length of 80 cm were produced. Table 1 presents the chemical composi- tion of AA6082 in accordance with standards. The chemical composition of the AA6082 aluminium alloy billets produced is provided in Table 2. The casting parameters used are detailed in Table 3. 350 vol. 65 no. 3/2025 Impact of process parameters on the mechanical and surface . . . Alloy Si Fe Cu Mn Mg Cr Zn [%] [%] [%] [%] [%] [%] [%] AA6082 0.7–1.3 0.50 0.10 0.40–1.0 0.6–1.2 0.25 0.20 Table 1. Standard chemical composition of AA6082. Cast Si Fe Cu Mn Mg Cr Zn [%] [%] [%] [%] [%] [%] [%] A 1.03 0.32 0.11 0.37 0.90 0.21 0.16 B 1.09 0.39 0.12 0.37 0.92 0.227 0.15 C 1.10 0.46 0.10 0.40 0.89 0.22 0.09 Table 2. Chemical analysis of AA6082. Cast Melting Casting Cooling water temperature [°C] speed [mm s−1] temp. [°C] A 701 119 24 B 699 120 25 C 711 115 25 Table 3. Casting parameters of AA6082. 2.2. Heat treatment process The 6XXX aluminium alloy series, defined as the Al- Mg-Si system, contains magnesium (Mg) and silicon (Si) as major elements. These key elements contribute to the formation of multiple phases. The multiphase structures that develop within the aluminium matrix influence the mechanical and physical properties of the alloy [13]. Solution heat treatment is recognised as the process responsible for the formation of precipi- tate phases in aluminium matrices. These precipitate phases directly affect the mechanical properties [5]. Heat treatment of AA6082 is typically conducted at a sub-eutectic temperature of 580 °C for a specific du- ration to promote the formation of precipitate phases in aluminium matrices [14]. Two different combina- tions of temperature and time were used during the heat treatment process. The parameters of the heat treatment process are provided in Table 4. Şahbaz M. [15], has studied the effect of the change of microstructure and mechanical properties of AA6082 aluminium alloy. Different cooling pro- cesses were performed on the annealed aluminium billet samples. It was reported that the grain size decreases depending on the cooling rate after the heat treatment process. This decreasing of the grain size is directly related to the strength of the sample. Also, the type of phases formed in the aluminium matrix was affected by cooling rate and cooling type. 2.3. Extrusion process One of the most critical factors in improving the sur- face quality and mechanical properties of aluminium profiles is the optimisation of extrusion process pa- rameters, such as aluminium billet and die temper- ature (°C), extrusion speed (mm s−1), and cooling Temperature [°C] Time [hour] 580 8 580 10 Table 4. Heat treatment of AA6082. conditions. These parameters are essential due to their role in continuously improving the microstruc- ture. The extrusion process is typically conducted at temperatures between 500 °C and 520 °C [16]. Ex- trusion is also defined as a thermomechanical process that involves the application of high temperature and pressure. The temperature applied is crucial to ensure an isothermal extrusion process [17]. Table 5 presents the extrusion process parameters used. Water shock cooling was also implemented during the extrusion process to enhance the mechanical prop- erties of the aluminium profiles. It is well-known that water shock cooling directly influences the mechanical properties and surface quality of extruded aluminium profiles. Additionally, a nitrogen gas cooling system was used in the extrusion process of AA6082, with cooling channels positioned on the extrusion steel die. This cooling system helps to prevent uncontrolled oxidation on the surface of the aluminium profile. 2.4. Artificial ageing process The ageing process is the final stage for improving the mechanical properties of the extruded aluminium profile. Table 6 shows the artificial ageing process parameters. 351 Bilgehan Tunca, Bahadır Karaca Acta Polytechnica Alloy Press [ton] Billet Billet Die Press Press Press Cooling systemlength temperature temperature speed pressure time [mm] [°C] [°C] [mm s−1] [bar] [s] AA6082 2 500 540 480 450 3.7 210 132 on Table 5. Extrusion process parameters. Temperature [°C] Time [hour] 180 6 180 8 180 10 Table 6. Artificial ageing parameters. 2.5. Anodic oxidation process The efficacy of the extrusion process plays a critical role in determining the quality of the surface finishing process and the surface quality of the extruded alu- minium profile. The anodic oxidation process, a sur- face finishing technique, is performed to induce a con- trolled form of oxidation on the aluminium surface. Anodic oxidation, also defined as an electrochemi- cal process, utilizes various chemical solutions, volt- age (V), and current (A). This process is widely used to improve aluminium surface quality and expand its use in industrial applications [18]. Table 7 presents the parameters of the anodic oxidation process. At this stage, a pre-surface finishing process was conducted to prepare the aluminium surface for an- odic oxidation. This pre-surface finishing process dissolves the uncontrolled oxide layer, which typically has a thickness of less than 1–2 µm [19]. Different anodic oxidation parameters were applied to investi- gate the thickness of the aluminium profile coating. The process parameters, specifically time and volt- age, directly influence the thickness of the aluminium coating. 3. Results and discussion 3.1. Mechanical test Mechanical tests were conducted on all samples with varying chemical compositions using a ZwickRoell ma- chine with a capacity of 20 tonnes. Tensile strength, yield strength, and percentage elongation were deter- mined. Three different chemical compositions were used in the production of the AA6082 series aluminium alloys. Additionally, each chemical composition was subjected to two distinct homogenisation processes, involving specific temperatures (°C) and durations (h. Subsequently, the homogenised samples were sub- jected to three different ageing processes, also defined by temperature (°C) and time (h). Mechanical testing was conducted on selected samples, with the reported values representing the mean of five measurements for each sample. Table 8 presents the results of the mechanical test, with the highest tensile strength (Rm) of 361 MPa observed for sample B2. Several factors contribute to this superior performance, stemming from the com- bined effects of casting conditions, heat treatment parameters, and microstructural characteristics. The chemical composition of Cast-B, from which B2 is derived, includes slightly higher Mg (0.92 %) and Si (1.09 %) contents compared to Cast-A (Mg: 0.90 %, Si: 1.03 %) and Cast-C (Mg: 0.89 %, Si: 1.10 %), as shown in Table 2. These elements are critical in the Al-Mg-Si system for forming β′′ (Mg2Si) precipitates, which improve precipitation hardening and thus con- tribute to strength. Although the compositional dif- ferences are subtle, they likely provided a marginal ad- vantage in strengthening B2. Additionally, the casting parameters for Cast-B (Table 3) reveal a higher casting speed (120 mm s−1) and a lower pouring temperature (699 °C) compared to Cast-A (119 mm s−1, 701 °C) and Cast-C (115 mm s−1, 711 °C). The elevated cast- ing speed likely reduced solidification time, promoting finer grain sizes, which are known to increase strength according to the Hall-Petch relationship. The lower pouring temperature may have further prevented ex- cessive grain growth, optimising the microstructure. The homogenisation process for B2, conducted at 580 °C for 8 hours, appears to have struck an optimal balance. In contrast, samples subjected to 10-hour homogenisation (e.g. B4–B6) consistently exhibited lower tensile strengths (e.g. B6: 313 MPa), possibly due to over-ageing or coarsening of precipitates. This suggests that the 8-hour duration preserved the size and distribution of β′′ precipitates effectively. Simi- larly, the artificial ageing process at 180 °C for 8 hours produced ideal conditions for precipitation hardening. Samples aged for 6 hours (e.g. B1: 298 MPa) showed insufficient hardening, while those aged for 10 hours (e.g. B3: 351 MPa) approached but did not surpass B2, indicating that 8 hours is optimal for precipitate formation without leading to over-ageing. Microstructural analysis (Section 3.2) further sup- ports these findings, as B2 exhibited smaller, more homogenised grain sizes and fewer inclusions com- pared to samples such as A1, C1, and C2. The rapid water shock cooling and nitrogen gas cooling applied during extrusion (Table 5) likely enhanced this effect by maintaining precipitate solubility and promoting a refined microstructure, which translated into supe- rior mechanical properties during ageing. In summary, the highest tensile strength of 361 MPa in B2 is attributed to a synergy of factors: a slightly 352 vol. 65 no. 3/2025 Impact of process parameters on the mechanical and surface . . . Solution Voltage Time [g L−1] [V] [minutes] 180 g L−1 sulfuric acid (H2SO4) 18 26 180 g L−1 sulfuric acid (H2SO4) 18 32 Table 7. Anodic oxidation parameters. Samples Homogenization Hardness [HB] Aging Yield Tensile Elongation [%]parameters parameters strength Rp0.2 strength Rm [°C – hour] [°C – hour] [MPa] [MPa] A1 580 °C – 8 h 103 180 °C – 6 h 308 331 11.5 A2 580 °C – 8 h 103 180 °C – 8 h 319 342 12.6 A3 580 °C – 8 h 103 180 °C – 10 h 307 318 10.4 A4 580 °C – 10 h 105 180 °C – 6 h 292 309 9.7 A5 580 °C – 10 h 105 180 °C – 8 h 288 304 9.2 A6 580 °C – 10 h 105 180 °C – 10 h 272 296 9.1 B1 580 °C – 8 h 103 180 °C – 6 h 281 298 9.3 B2 580 °C – 8 h 103 180 °C – 8 h 321 361 13.0 B3 580 °C – 8 h 103 180 °C – 10 h 332 351 12.8 B4 580 °C – 10 h 105 180 °C – 6 h 292 311 9.6 B5 580 °C – 10 h 105 180 °C – 8 h 284 318 9.9 B6 580 °C – 10 h 105 180 °C – 10 h 292 313 9.6 C1 580 °C – 8 h 103 180 °C – 6 h 317 322 10.3 C2 580 °C – 8 h 103 180 °C – 8 h 299 319 9.9 C3 580 °C – 8 h 103 180 °C – 10 h 287 307 9.4 C4 580 °C – 10 h 105 180 °C – 6 h 288 302 9.4 C5 580 °C – 10 h 105 180 °C – 8 h 272 296 9.1 C6 580 °C – 10 h 105 180 °C – 10 h 267 289 8.9 Table 8. Mechanical test results. favourable chemical composition, a higher casting speed leading to finer grains, an 8-hour homogenisa- tion process preventing precipitate coarsening, and an 8-hour ageing process optimising β′′ precipitate forma- tion. These conditions collectively outperformed other samples, such as A2 (342 MPa) and B3 (351 MPa), where variations in casting speed or ageing duration were less optimal, and C-series samples, which suffered from slower casting speeds and larger grain sizes. Chen et al. [20] reported that 6XXX series alu- minium alloys tend to exhibit lower strain rate sen- sitivity compared to 7XXX series aluminium alloys. Heat treatment directly affects the mechanical prop- erties of aluminium alloys. Oosterkamp et al. [21] found that AA6082, in T6 and T79 temper conditions, displayed low strain rate sensitivity. Jadhav et al. [22] investigated the effect of various artificial ageing tem- peratures (ranging from 150 °C to 210 °C) on the me- chanical properties of AA6082. Their study reported that the peak strength was achieved at a temperature of 170 °C. 3.2. Microstructure analysis The microstructures and grain sizes of the six sam- ples exhibiting the highest tensile test results were analysed. For the microstructural analysis, the sam- ples were not etched, whereas etching was performed for grain size evaluation. All microstructure images were observed at 100× magnification. Grain size ex- aminations were conducted at various magnifications. Figure 1 presents the images of samples A1, A2, and B2, while Figure 2 displays the images of samples B3, C1, and C2. In the sample examinations, grain sizes between 110 and 205 µm were examined. The best results were obtained for samples A2, B2 and B3. Inclusion formations in their microstructures are lower than in the other three samples (A1, C1 and C2) and grain sizes are more homogenised and smaller. Figure 3 shows the grain size. When examining grain sizes, a significant difference was observed between samples A2 and C2. A detailed analysis suggests several potential reasons for this disparity. Firstly, when the homogenisation process parameters – temperature and duration – were evalu- ated, both appeared consistent and identical for the two samples. This indicates that the homogenisation conditions are unlikely to directly contribute to the observed variation in grain size. Similarly, an analysis of the chemical compositions, measured using spectro- scopic techniques (e.g. XRF or ICP-OES), revealed no significant differences in elemental content, suggesting 353 Bilgehan Tunca, Bahadır Karaca Acta Polytechnica (a). Structures of sample A1. (b). Structures of sample A2. (c). Structures of sample B2. Figure 1. Microstructure and grain sizes of the samples. that the chemical composition alone cannot account for the observed discrepancy. However, more pronounced clues emerge when ex- amining the casting conditions. The C2 sample, asso- ciated with the Cast-C process, had a pouring tem- perature of 711 °C, which is lower than that of the Cast-A and Cast-B processes. Furthermore, the cast- ing speed for Cast-C was observed lower compared to the other two casting processes (Cast-A and Cast-B). It is well-established that parameters such as casting speed and temperature directly influence the solidifi- cation kinetics and microstructure formation of liquid metal. Specifically, a lower casting speed extends the solidification time, potentially promoting grain growth, as slower cooling rates allow more time for dendritic structures to develop. Indeed, the grain sizes of samples from Cast-A and Cast-B were observed to be smaller than those of Cast-C, supporting the hy- pothesis that differences in casting conditions impact grain size. Nevertheless, casting conditions alone may not fully explain this variation. The possibility of a localised 354 vol. 65 no. 3/2025 Impact of process parameters on the mechanical and surface . . . (a). Structures of sample B3. (b). Structures of sample C1. (c). Structures of sample C2. Figure 2. Microstructure and grain sizes of the samples. temperature increase during casting should not be overlooked. For instance, irregularities in the molten metal’s flow dynamics within the mould or an uncon- trolled rise in mould temperature could lead to uneven advancement of the solidification front, resulting in grain size heterogeneity. Additionally, a reduction in the amount of AlTiB (Aluminium-Titanium-Boron) alloy used as a grain refiner may have contributed to this effect. AlTiB facilitates grain refinement by providing TiB2 particles that act as nucleation sites within the molten metal. If the AlTiB dosage in the C2 sample’s casting was insufficient or inadequately distributed, this could have resulted in larger grain sizes. Verifying this hypothesis would require moni- toring the AlTiB dosage and its mixing homogeneity during the process. In conclusion, while variations in casting tempera- ture and speed appear to be the primary contributors to the grain size differences, factors such as temper- ature fluctuations and potential deficiencies in grain refiner quantity should also be considered. For future studies, a systematic experimental design is recom- 355 Bilgehan Tunca, Bahadır Karaca Acta Polytechnica Figure 3. Graph of grain size. mended to control and optimise these parameters com- prehensively. For example, casting temperature could be incrementally increased from 700 °C to 750 °C, cast- ing speed could be tested at varying flow rates, and AlTiB dosage (e.g. from 0.5 kg ton−1 to 2 kg ton−1) could be systematically adjusted, with its impact on grain size analysed using statistical methods such as ANOVA. Furthermore, advanced microstructural char- acterisation techniques, such as optical microscopy or EBSD (Electron Backscatter Diffraction), could be used to provide a more detailed examination of grain size distribution and crystallographic orientation. Such an approach would establish a more precise re- lationship between process parameters and grain size outcomes. 3.3. SEM analysis SEM analysis was conducted to investigate the sur- face characteristics following the homogenisation heat treatment. The analysis was performed on samples A2, B2, and B3, which exhibited superior mechan- ical properties. Figure 4 presents SEM images of these different samples. Figure 5 displays the SEM analysis of the anodic oxidation surface. The examina- tions were carried out using an FEI Quanta 650 Field Emission SEM under vacuum conditions at various magnifications at the Çukurova University Central Research Laboratory. Additionally, SEM analysis was performed to examine the fracture surfaces of these samples. When a comparative analysis of SEM (Scanning Electron Microscopy) images was conducted, it was clearly observed that the fracture surface of the B3 casting sample exhibits a significantly more ductile microstructure than the other SEM images analysed. This ductile character is evident from the presence of pronounced plastic deformation traces on the fracture surface and the predominance of microscopic features typically associated with ductile fracture such as dim- ple formations. In contrast to the other samples, this distinction in the fracture surface of B3 reflects a variation in the material’s mechanical behaviour. Consequently, it can be predicted that this ductile behaviour is directly related to the material’s key me- chanical properties, such as toughness and strength. Specifically, a ductile microstructure generally indi- cates a higher energy absorption capacity and the ability of the material to undergo greater deforma- tion prior to fracture, suggesting that the B3 sample may possess superior fracture toughness compared to the others. The underlying reasons for this difference could stem from factors, such as casting conditions, chemical composition, or heat treatment parameters, warranting a more detailed investigation to elucidate the contributing factors. 4. Conclusion This study explored the influence of chemical compo- sition and heat treatment processes on the mechanical and microstructural properties of AA6082 aluminium alloy, with a focus on optimising these properties for industrial applications. Three distinct chemical compositions were subjected to homogenisation heat treatment at 580 °C for 8 and 10 hours, followed by artificial ageing at 180 °C for 6, 8, and 10 hours. The resulting 18 samples were analysed through tensile testing, microstructural examination, SEM analysis, and anodic oxidation assessments to evaluate the ef- fects of these parameters. Additionally, the anodising process was conducted with two sets of parameters (18 V for 26 and 32 minutes) to investigate the quality of the surface coating. The mechanical test results demonstrated that the highest tensile strength (361 MPa) and yield strength (332 MPa) were achieved for samples A2, B2, and B3, with B2 exhibiting the peak tensile strength af- ter 8 hours of homogenisation at 580 °C and 8 hours of ageing at 180 °C. This superior performance is at- tributed to a synergy of factors, including a slightly elevated Mg (0.92 %) and Si (1.09 %) content in Cast- B, a higher casting speed (120 mm s−1), and a lower pouring temperature (699 °C), which promoted finer grain sizes and optimal β′′ (Mg2Si) precipitate distri- bution. In contrast, samples homogenised for 10 hours 356 vol. 65 no. 3/2025 Impact of process parameters on the mechanical and surface . . . (a). SEM images of the A2 sample. (b). SEM images of the B2 sample. (c). SEM images of the B3 sample. Figure 4. SEM images of the samples. showed reduced strength, likely due to over-ageing, while the 8-hour homogenisation and ageing durations struck an ideal balance for precipitation hardening. Microstructural analysis revealed that the 10-hour ho- mogenisation process resulted in fewer shrinkage gaps along grain boundaries and reduced surface poros- ity compared to the 8-hour treatment, indicating im- proved microstructural homogeneity with extended heat treatment time. The extrusion process, improved by direct wa- ter shock cooling, positively impacted surface qual- ity and hardness. Post-extrusion surfaces exhibited a smoother, more homogeneous texture, attributed to rapid cooling that preserved precipitate solubility and refined the microstructure. The use of a nitrogen gas cooling system during the extrusion further reduced thermal fatigue in the die steels, despite their high thermal conductivity, thereby improving surface qual- ity and extending the die longevity. These findings underscore the critical role of cooling strategies in achieving high-quality aluminium profiles. The SEM analysis of the fracture surfaces revealed that samples with the highest mechanical properties, such as B3 (yield strength: 332 MPa), exhibited more 357 Bilgehan Tunca, Bahadır Karaca Acta Polytechnica (a). SEM images of the A2 sample. (b). SEM images of the B2 sample. (c). SEM images of the B3 sample. Figure 5. SEM images of the anodic oxidised surfaces of samples. ductile behaviour, characterised by less dense fibrous structures and wider grain size distributions. This duc- tility correlates with improved toughness, influenced by the temperature and duration of the homogenisa- tion process, which directly shaped the grain structure and precipitate morphology. Conversely, samples with shorter ageing times (e.g. 6 hours) showed insufficient hardening, while prolonged ageing (10 hours) risked over-ageing, highlighting the need for a precise param- eter control. The anodizing process, leveraging aluminium’s natu- ral oxide-forming tendency, produced controlled oxide layers with thicknesses ranging from 10.6 to 11.7 µm and improved gloss. The thickest and brightest coat- ings were achieved at 18 V for 32 minutes, particularly for samples homogenised at 580 °C for 8 hours and aged at 180 °C for 8 hours (e.g. B2). This suggests that the homogenisation and ageing processes not only enhance mechanical properties but also influence the surface treatment quality, likely by affecting the alloy’s surface reactivity and microstructure prior to anodising. The coating thicknesses and gloss of the samples as a result of the anodic oxidation process are given in Table 9. 358 vol. 65 no. 3/2025 Impact of process parameters on the mechanical and surface . . . Sample Homogenization Aging Voltage [V] Time [minutes] Coating GlossParameters Parameters Thickness [°C – h] [°C – h] [µm] A2 580 °C-8 h 180°C-8 h 18 26 10.8 53 32 11.4 54 B2 580 °C-8 h 180 °C-8 h 18 26 10.6 51 32 11.6 55 B3 580 °C-8 h 180 °C-10 h 18 26 10.9 52 32 11.7 57 Table 9. Anodic oxidation results. In summary, the mechanical properties, microstruc- tural integrity, and surface quality of AA6082 alu- minium alloy are governed by a complex interplay of chemical composition, heat treatment duration, cooling techniques, and anodising parameters. The optimal conditions identified, which are 8-hour ho- mogenisation at 580 °C, 8-hour ageing at 180 °C, and rapid cooling during the extrusion, yielded the highest strength (361 MPa) and ductility, as observed for B2, while also supporting superior anodic coating. Future research could further refine these outcomes by sys- tematically varying casting and cooling parameters, exploring grain refiner effects (e.g. AlTiB dosage), and using advanced techniques such as EBSD to deepen the understanding of microstructural evolution. These advancements could significantly improve the perfor- mance of high-strength aluminium profiles in indus- trial applications. Key takeaways (1.) Optimal Heat Treatment Parameters: Homogeni- sation at 580 °C for 8 hours followed by artificial ageing at 180 °C for 8 hours yielded the highest me- chanical properties for AA6082, with a peak tensile strength of 361 MPa (B2 sample), demonstrating the importance of balanced heat treatment dura- tions to maximise precipitation hardening without over-ageing. (2.) Influence of Chemical Composition and Casting: Slight increases in Mg (0.92 %) and Si (1.09 %) content, combined with a higher casting speed (120 mm s−1) and lower pouring temperature (699 °C), improved grain refinement and β′′ pre- cipitate formation, significantly boosting strength and ductility. (3.) Cooling Benefits in Extrusion: Direct water shock cooling and nitrogen gas cooling during extrusion improved surface smoothness, hardness, and mi- crostructural homogeneity while reducing die ther- mal fatigue, highlighting cooling as a critical factor in profile quality. (4.) Microstructural Effects: Compared to 8 hours, longer homogenisation (10 hours) reduced shrinkage gaps and porosity. However, optimal mechanical properties were associated with smaller, more uni- form grain sizes and ductile fracture surfaces, as observed in B2 and B3 via SEM analysis. (5.) Anodizing Performance: Anodizing at 18 V for 32 minutes produced thicker (up to 11.7 µm) and glossier oxide layers, with surface quality linked to prior homogenisation and ageing processes, empha- sizing their role beyond mechanical enhancement. Acknowledgements The authors would like to express their gratitude to Za- hit Alüminyum and Sistem Alüminyum companies for supporting this paper. References [1] A. Mozalev, A. Poznyak, I. Mozaleva, A. W. Hassel. The voltage-time behaviour for porous anodizing of aluminium in a fluoride-containing oxalic acid electrolyte. Electrochemistry Communications 3(6):299–305, 2001. https://doi.org/10.1016/S1388-2481(01)00157-6 [2] Q. Li, J. O. Jensen, N. J. Bjerrum. Chemistry, electrochemistry, and electrochemical applications: Aluminum. In Encyclopedia of Electrochemical Power Sources, pp. 695–708. Elsevier, United Kingdom, 2009. https://doi.org/10.1016/B978-044452745-5.00951- 5 [3] P. Schempp, C. E. Cross, C. Schwenk, M. Rethmeier. Influence of Ti and B additions on grain size and weldability of aluminium alloy 6082. Welding in the World 56(9):95–104, 2012. https://doi.org/10.1007/BF03321385 [4] G. Mrówka-Nowotnik. Influence of chemical composition variation and heat treatment on microstructure and mechanical properties of 6XXX alloys. Archives of Materials Science and Engineering 46(2):98–107, 2010. [5] G. Mrówka-Nowotnik, J. Sieniawski. Influence of heat treatment on the microstructure and mechanical properties of 6005 and 6082 aluminium alloys. Journal of Materials Processing Technology 162–163:367–372, 2005. https: //doi.org/10.1016/j.jmatprotec.2005.02.115 [6] A. R. Prabhukhot, K. Prasad. Effect of heat treatment on hardness of 6082-T6 aluminum alloy. International Journal of Scientific & Engineering Research 6(12):38–42, 2015. 359 https://doi.org/10.1016/S1388-2481(01)00157-6 https://doi.org/10.1016/B978-044452745-5.00951-5 https://doi.org/10.1016/B978-044452745-5.00951-5 https://doi.org/10.1007/BF03321385 https://doi.org/10.1016/j.jmatprotec.2005.02.115 https://doi.org/10.1016/j.jmatprotec.2005.02.115 Bilgehan Tunca, Bahadır Karaca Acta Polytechnica [7] W. Ma, B. Wang, L. Yang, et al. Influence of solution heat treatment on mechanical response and fracture behaviour of aluminium alloy sheets: An experimental study. Materials & Design 88:1119–1126, 2015. https://doi.org/10.1016/j.matdes.2015.09.044 [8] M. W. Meredith, J. Worth, R. Hamerton. Intermetallic phase selection during solidification of Al- Fe-Si(-Mg) alloys. In Aluminium Alloys 2002 – ICAA8, vol. 396–402 of Materials Science Forum, pp. 107–112. Trans Tech Publications Ltd, 2002. https://doi.org/ 10.4028/www.scientific.net/MSF.396-402.107 [9] G. Sha, K. O’Reilly, B. Cantor, et al. Effect of grain refiner on intermetallic phase formation in directional solidification of 6XXX series wrought Al alloys. In Aluminium Alloys – Their Physical and Mechanical Properties, vol. 331–337 of Materials Science Forum, pp. 253–258. Trans Tech Publications Ltd, 2000. https://doi.org/10.4028/www.scientific.net/MSF. 331-337.253 [10] T. Tokarski. Thermo-mechanical processing of rapidly solidified 5083 aluminium alloy – structure and mechanical properties. Archives of Metallurgy and Materials 60(1):177–180, 2015. https://doi.org/10.1515/amm-2015-0028 [11] P. K. Saha. Thermodynamics and tribology in aluminum extrusion. Wear 218(2):179–190, 1998. https://doi.org/10.1016/S0043-1648(98)00210-5 [12] O. Engler, S. Miller-Jupp. Control of second-phase particles in the Al-Mg-Mn alloy AA5083. Journal of Alloys and Compounds 689:998–1010, 2016. https://doi.org/10.1016/j.jallcom.2016.08.070 [13] P. S. Mohanty, J. E. Gruzleski. Mechanism of grain refinement in aluminium. Acta Metallurgica et Materialia 43(5):2001–2012, 1995. https://doi.org/10.1016/0956-7151(94)00405-7 [14] O. Güven. Structural analysis of Al-Si-Mg casting alloy. Master’s thesis, Istanbul Technical University, 2005. [15] M. Şahbaz. Effect of artificial aging and cooling rate on microstructure and mechanical properties of AA6082. European Journal of Science and Technology (28):300–305, 2021. https://doi.org/10.31590/ejosat.998077 [16] T. Björk, R. Westergård, S. Hogmark. Wear of surface treated dies for aluminium extrusion – A case study. Wear 249(3–4):316–323, 2001. https://doi.org/10.1016/S0043-1648(01)00550-6 [17] O. Olaseinde, B. Adewuyi. Effect of ceramic powder coatings on low carbon steel. Materials Sciences and Applications 7(5):221–231, 2016. https://doi.org/10.4236/msa.2016.75022 [18] E. Cirik, K. Genel. Effect of anodic oxidation on fatigue performance of 7075-T6 alloy. Surface and Coatings Technology 202(21):5190–5201, 2008. https://doi.org/10.1016/j.surfcoat.2008.06.049 [19] M. Ardelean, S. Lascău, E. Ardelean, A. Josan. Surface treatments for aluminium alloys. IOP Conference Series: Materials Science and Engineering 294(1):012042, 2018. https://doi.org/10.1088/1757-899X/294/1/012042 [20] Y. Chen, A. H. Clausen, O. S. Hopperstad, M. Langseth. Stress-strain behaviour of aluminium alloys at a wide range of strain rates. International Journal of Solids and Structures 46(21):3825–3835, 2009. https://doi.org/10.1016/j.ijsolstr.2009.07.013 [21] L. Djapic Oosterkamp, A. Ivankovic, G. Venizelos. High strain rate properties of selected aluminium alloys. Materials Science and Engineering: A 278(1–2):225–235, 2000. https://doi.org/10.1016/S0921-5093(99)00570-5 [22] S. Jadhav, R. Singh, V. Pawar, S. Mane. Influence of heat treatment on mechanical properties and microstructure of EN AW 6082 aluminum alloy. In 2017 8th International Conference on Mechanical and Aerospace Engineering (ICMAE), pp. 184–187. 2017. https://doi.org/10.1109/ICMAE.2017.8038639 360 https://doi.org/10.1016/j.matdes.2015.09.044 https://doi.org/10.4028/www.scientific.net/MSF.396-402.107 https://doi.org/10.4028/www.scientific.net/MSF.396-402.107 https://doi.org/10.4028/www.scientific.net/MSF.331-337.253 https://doi.org/10.4028/www.scientific.net/MSF.331-337.253 https://doi.org/10.1515/amm-2015-0028 https://doi.org/10.1016/S0043-1648(98)00210-5 https://doi.org/10.1016/j.jallcom.2016.08.070 https://doi.org/10.1016/0956-7151(94)00405-7 https://doi.org/10.31590/ejosat.998077 https://doi.org/10.1016/S0043-1648(01)00550-6 https://doi.org/10.4236/msa.2016.75022 https://doi.org/10.1016/j.surfcoat.2008.06.049 https://doi.org/10.1088/1757-899X/294/1/012042 https://doi.org/10.1016/j.ijsolstr.2009.07.013 https://doi.org/10.1016/S0921-5093(99)00570-5 https://doi.org/10.1109/ICMAE.2017.8038639 Acta Polytechnica 65(3):349–360, 2025 1 Introduction 2 Material and methods 2.1 Billet casting process 2.2 Heat treatment process 2.3 Extrusion process 2.4 Artificial ageing process 2.5 Anodic oxidation process 3 Results and discussion 3.1 Mechanical test 3.2 Microstructure analysis 3.3 SEM analysis 4 Conclusion Acknowledgements References