Theoretical and Experimental Analysis of the Hot Torsion Process of the Hardly Deformable 5XXX Series Aluminium Alloy

Abstract

This work presents the results of the numerical and physical modelling of the hot torsion of a hardly deformable 5XXX series aluminium alloy. Studies were conducted on constrained torsion with the use of the STD 812 torsion plastometer. The main purpose of the numerical tests was to determine the influence of the accuracy of the mathematical model describing the changes in the yield stress of the tested material on the distribution of strain parameters and on the stress intensity. According to the preliminary studies, in the case of numerical modelling of the torsion test, the accuracy of the applied mathematical model describing the changes in the rheological properties of the tested material and the correct definition of the initial and boundary conditions had a particularly significant impact on the correctness of the determination of the strain parameters and the intensity of stresses. As part of the experimental tests, physical modelling of the hot torsion test was conducted. The aim of this part of the work was to determine the influence of the applied strain parameters on the distribution and size of grain as well as the microhardness of the tested aluminium alloy. Metallographic analyses were performed using light microscopy and the electron backscatter diffraction method. Due to the large inhomogeneity of the deformation parameters and the stress intensity in the torsion test, such tests were necessary for the correct determination of the so-called representative area for metallographic analyses. These types of studies are particularly important in the case of the so-called complex deformation patterns. The paper also briefly presents the results of preliminary research and future directions in which it is planned to use complex deformation patterns for physical modelling of selected processes combining various materials.

Keywords: EBSD analysis; hardly deformable materials; hot torsion test; inhomogeneity of microstructure; metallographic examinations; microhardness; numerical modelling; physical modelling; strain and stress state.

Figure 1

STD 812 torsion plastometer: (a) device chamber: 1—specimen, 2—holders, 3—thermocouples type S, 4—induction solenoid, 5—cooling system jets, 6—pyrometer and 7—sensors for laser measurement of specimen diameter; (b) basic specification.

Figure 2

The 5019 aluminium alloy sample’s technical specification.

Figure 3

Example specimen during welding of the thermocouple with a lateral surface.

Figure 4

Actual temperature distribution along the sample’s length determined by the contact method.

Figure 5

Flow curves of the 5019 aluminium alloy at temperatures of (a) 440 °C; (b) 480 °C; (c) 520 °C; empty symbols—plastometric test data; full symbols—results after approximation using coefficients from Table 1 (Variant 1).

Figure 6

Temperature distribution of the 5019 aluminium alloy calculated numerically using coefficients from Table 1: (a) at the beginning of the torsion—longitudinal section, (b) at the end of the torsion—longitudinal section, (c) at the end of the torsion—cross-section in the centre of the working part of the sample and (d) at the end of the torsion—perspective.

Figure 7

Distribution of the strain intensity of the 5019 aluminium alloy calculated numerically using coefficients from Table 1: (a) longitudinal section, (b) cross-section—centre of the working part and (c) perspective.

Figure 8

Distribution of the strain rate intensity of the 5019 aluminium alloy calculated numerically using coefficients from Table 1: (a) longitudinal section, (b) cross-section—centre of the working part and (c) perspective.

Figure 9

Distribution of the stress intensity of the 5019 aluminium alloy calculated numerically using coefficients from Table 1: (a) longitudinal section, (b) cross-section—centre of the working part and (c) perspective.

Figure 10

Flow curves of the 5019 aluminium alloy at temperatures of (a) 440 °C; (b) 480 °C; (c) 520 °C; empty symbols—plastometric test data; full symbols—results after approximation using coefficients from Table 2 (Variant 2).

Figure 11

Distribution of the strain intensity of the 5019 aluminium alloy calculated numerically using coefficients from Table 2: (a) longitudinal section, (b) cross-section—centre of the working part and (c) perspective.

Figure 12

Distribution of the strain rate intensity of the 5019 aluminium alloy calculated numerically using coefficients from Table 2: (a) longitudinal section, (b) cross-section—centre of the working part and (c) perspective.

Figure 13

Distribution of the stress intensity of the 5019 aluminium alloy calculated numerically using coefficients from Table 2: (a) longitudinal section, (b) cross-section—centre of the working part and (c) perspective.

Figure 14

Changes in the torque and yield stress of the 5019 aluminium alloy—true and calculated values.

Figure 15

Cross-section of the sample with marked directions in which metallographic tests and microhardness measurements were carried out (general diagram).

Figure 16

Microstructure of the 5019 aluminium alloy in initial state, after the homogenisation process (before the deformation process): (a) cross-section; (b) longitudinal section.

Figure 17

Microstructure of the 5019 aluminium alloy in the initial state, after the homogenisation process (before the deformation process): (a) sample centre; (b) sample edge; cross-section, magnification 200×.

Figure 18

Changes in the grain size on the cross-section of the sample made of the 5019 aluminium alloy; the measurements were performed in two perpendicular directions (as shown in Figure 15); P0—the initial state of the material (after homogenisation).

Figure 19

Microstructure of the 5019 aluminium alloy after plastic deformation: (a) cross-section; (b) longitudinal section.

Figure 20

Microstructure of the 5019 aluminium alloy after plastic deformation: (a) centre of the sample; (b) edge of the sample; cross-section, magnification 200×.

Figure 21

Changes in the grain size on the cross-section of a sample from the 5019 aluminium alloy after the deformation process; the measurements were made in two perpendicular directions (as shown in Figure 15); P1—material condition after hot torsion.

Figure 22

Changes in microhardness on the cross-section of the 5019 aluminium alloy samples (measurements made in two perpendicular directions—according to Figure 14): (a) undeformed material; (b) material after plastic deformation.

Figure 23

EBSD analysis results of the sample after homogenisation; (a,b,c) centre of the sample, (d,e,f) distance from the centre = 0.67 r, (g,h,i) distance of the centre = 0.72 r; (a,d,g) EBSD maps showing changes in orientation, (b,e,h) maps showing the types of edges (the edges of a large angle are marked in black, and the edges of a small angle are marked in blue) and a (c,f,i) basic triangle—orientation intensity.

Figure 23

EBSD analysis results of the sample after homogenisation; (a,b,c) centre of the sample, (d,e,f) distance from the centre = 0.67 r, (g,h,i) distance of the centre = 0.72 r; (a,d,g) EBSD maps showing changes in orientation, (b,e,h) maps showing the types of edges (the edges of a large angle are marked in black, and the edges of a small angle are marked in blue) and a (c,f,i) basic triangle—orientation intensity.

Figure 24

EBSD analysis results of the sample after deformation: (a,b,c) centre of the sample, (d,e,f) distance from the centre = 0.67 r, (g,h,i) distance of the centre = 0.72 r; (a,d,g) EBSD maps showing changes in orientation, (b,e,h) maps showing the types of edges (the edges of a large angle are marked in black, and the edges of a small angle are marked in blue) and a (c,f,i) basic triangle—orientation intensity.

Figure 24

EBSD analysis results of the sample after deformation: (a,b,c) centre of the sample, (d,e,f) distance from the centre = 0.67 r, (g,h,i) distance of the centre = 0.72 r; (a,d,g) EBSD maps showing changes in orientation, (b,e,h) maps showing the types of edges (the edges of a large angle are marked in black, and the edges of a small angle are marked in blue) and a (c,f,i) basic triangle—orientation intensity.

Figure 25

Changes in disorientation angles after hot torsion: (a) sample centre, (b) at a distance from the centre of 0.67 r and (c) at a distance from the centre of 0.72 r.

Figure 26

6XXX series aluminium alloy sample: (a) before the friction welding process; (b) after the friction welding process.

Figure 27

Temperature, length and angle of rotation changes over time in the first stage of friction welding of the aluminium 6XXX series—simultaneous torsion with compression.

Figure 28

Changes in the true strain torsion, true stress torsion and true strain rate torsion over time in the first stage of friction welding of the 6XXX series aluminium—simultaneous torsion with compression components resulting from torsion.

Figure 29

Changes in the true strain deformation, true stress deformation and force over time in the first stage of friction welding of the aluminium 6XXX series—simultaneous torsion with compression components resulting from compression.

Figure 30

Temperature and length changes over time in the second stage of the friction welding of the 6XXX series aluminium—compression.

Figure 31

Changes in the true strain deformation, true stress deformation and force over time in the second stage of the friction welding of the 6XXX series aluminium—compression.