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Analysis of the influence of dies geometry on the process extrusion force and properties of the extrudate obtained in the process of cold extrusion of 7075 aluminum alloy by the KOBO method

Marek Zwolak

Marek Zwolak

Department of Materials Forming and Processing, The Faculty of Mechanical Engineering and Aeronautics, Rzeszów University of TechnologyRzeszów, Poland
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Zwolak, Marek
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Romana Śliwa

Romana Śliwa

Department of Materials Forming and Processing, The Faculty of Mechanical Engineering and Aeronautics, Rzeszów University of TechnologyRzeszów, Poland
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Śliwa, Romana
  
22. Mai 2024
Analysis of the influence of dies geometry on the process extrusion force and properties of the extrudate obtained in the process of cold extrusion of 7075 aluminum alloy by the KOBO method's Cover Image
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Online veröffentlicht: 22. Mai 2024
Seitenbereich: 92 - 106
Eingereicht: 29. Dez. 2023
Akzeptiert: 24. Apr. 2024
DOI: https://doi.org/10.2478/msp-2024-0008
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© 2024 Marek Zwolak et al., published by Sciendo
This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

Fig. 1.

Schematic of KOBO extrusion process: 1- container sleeve, 2- butt, 3- die, 4- billet
Schematic of KOBO extrusion process: 1- container sleeve, 2- butt, 3- die, 4- billet

Fig. 2.

2500 kN KOBO extrusion press
2500 kN KOBO extrusion press

Fig. 3.

Macrostructure of the longitudinal section of the test material in the initial state (annealed 7075 aluminum alloy)
Macrostructure of the longitudinal section of the test material in the initial state (annealed 7075 aluminum alloy)

Fig. 4.

Microstructures of 7075 aluminum alloy initial condition, cross-section (a) and longitudinal section (b), 500x mag
Microstructures of 7075 aluminum alloy initial condition, cross-section (a) and longitudinal section (b), 500x mag

Fig. 5.

Sketch of characteristic features of dies for KOBO process
Sketch of characteristic features of dies for KOBO process

Fig. 6.

Dies used for experimental research
Dies used for experimental research

Fig. 7.

Graph of the extrusion force as a function of stem displacement
Graph of the extrusion force as a function of stem displacement

Fig. 8.

Graph of stress-strain relationships in static tensile test of extruded products – samples taken from three areas along the length of the extrudate – series 1
Graph of stress-strain relationships in static tensile test of extruded products – samples taken from three areas along the length of the extrudate – series 1

Fig. 9.

Graph of stress-strain relationships in static tensile test of extruded products – samples taken from three areas along the length of the extrudate – series 2
Graph of stress-strain relationships in static tensile test of extruded products – samples taken from three areas along the length of the extrudate – series 2

Fig. 10.

Graph of stress-strain relationships in static tensile test of extruded products – samples taken from three areas along the length of the extrudate – series 3
Graph of stress-strain relationships in static tensile test of extruded products – samples taken from three areas along the length of the extrudate – series 3

Fig. 11.

Macrostructure of 7075 alloy: front, 200x mag.; middle, 100x mag.; and end extrusion stages, 100x mag. Visible shear lines in the near-surface area
Macrostructure of 7075 alloy: front, 200x mag.; middle, 100x mag.; and end extrusion stages, 100x mag. Visible shear lines in the near-surface area

Fig. 12.

Macrostructure of alloy 7075 after conventional extrusion: front, middle and end extrusion stages, 100x mag. No clear shear lines, visible peripheral disruption of the alloy microstructure due to flow
Macrostructure of alloy 7075 after conventional extrusion: front, middle and end extrusion stages, 100x mag. No clear shear lines, visible peripheral disruption of the alloy microstructure due to flow

Fig. 13.

Microstructure of 7075 alloy: cross-sectional view of the near-surface area (a) and the area inside the bar (b), and longitudinal section of the near-surface area (c) and the area inside the bar (d), 500x mag
Microstructure of 7075 alloy: cross-sectional view of the near-surface area (a) and the area inside the bar (b), and longitudinal section of the near-surface area (c) and the area inside the bar (d), 500x mag

Fig. 14.

Microstructure of 7075 alloy typical of all tested KOBO samples in the near-surface zone (a and c, 200x mag.) and beyond (b and d, 1000x mag.). Longitudinal section, SEM
Microstructure of 7075 alloy typical of all tested KOBO samples in the near-surface zone (a and c, 200x mag.) and beyond (b and d, 1000x mag.). Longitudinal section, SEM

Fig. 15.

Microstructure of 7075 alloy, test NG (F): cross-section of the near-surface area (a) and the area inside the bar (b) and longitudinal cross-section of the near-surface area (c) and the area inside the bar (d), 500x mag
Microstructure of 7075 alloy, test NG (F): cross-section of the near-surface area (a) and the area inside the bar (b) and longitudinal cross-section of the near-surface area (c) and the area inside the bar (d), 500x mag

Fig. 16.

Microstructure of the extrudate, sample NG (F): longitudinal cross-section, visible inhomogeneity due to the banded structure of the rod, SEM, (a) 1000x mag., (b) & (c) 3000x mag
Microstructure of the extrudate, sample NG (F): longitudinal cross-section, visible inhomogeneity due to the banded structure of the rod, SEM, (a) 1000x mag., (b) & (c) 3000x mag

Mechanical properties of extrudate determined by static tensile test – series 1

Rp0.2 Rm A50
MPa MPa %
G8D1F 194.3767 319.763 16.82835
G8D1M 182.0377 325.0069 15.53416
G8D1E 191.4832 351.6311 17.21147
G8D2F 191.682 329.3694 16.09939
G8D2M 184.0032 325.3811 17.21048
G8D2E 174.6589 327.0506 14.48359
G8D3F 191.8396 326.371 18.55923
G8D3M 179.7999 322.9885 17.81401
G8D3E 187.1591 344.8309 14.46475

Mechanical properties of extrudate determined by static tensile test – series 2

Rp0.2 Rm A50
MPa MPa %
G6D1F 139.9892 375.7772 18.3135
G6D1M 203.2703 351.6911 15.75259
G6D1E 203.6512 357.1238 15.73096
G10D1F 219.1892 359.8165 17.40554
G10D1M 213.132 362.4292 17.7133
G10D1E 211.7307 372.7265 15.55199
G12D1F 228.0526 372.5014 16.29631
G12D1M 204.0853 361.9522 17.48726
G12D1E 217.7237 377.1663 13.81927

Mechanical properties of extrudate determined by static tensile test – series 3

Rp0.2 Rm A50
NG_KOBO F 227.5532 363.6127 11.61306
NG_KOBO M 210.6277 368.3837 37.3797
NG_KOBO E 194.2238 354.8399 16.83634
NG F 178.6093 314.8302 12.87594
NG M 178.4273 318.8969 27.68791
NG E 179.8115 303.1239 9.513819

Dimensions of the characteristic features of the dies used for experimental research

Code Number of grooves Grooves depth [mm]
G8D1 8 1
G8D2 8 2
G8D3 8 3
G6D1 6 1
G10D1 10 1
G12D1 12 1
NG – –

Maximum recorded extrusion forces in the KOBO process using different die types

Test Maximum extrusion force [kN] Comment
G8D1 2086 No container sleeve cleaning before test
G8D2 1962
G8D3 1962
G6D1 1924
G10D1 1906
G12D1 1890
NG KOBO 1923 Flat face die
NG 1458 Conventional extrusion at 450° C
Butt 79 Butt pushing force while cleaning container sleeve
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