Microstructural evolution and deformation behavior of copper alloy during rheoforging process

doi:10.1016/j.jmst.2019.09.036

Abstract

Abstract:

A complete rheo-forming process was carried out to investigate the rheoforging process of C3771 lead brass valve, starting from the semi-solid billet preparation to rheoforging experiments and material performance tests. The near-spherical micro-grains with mean equivalent diameter of 56.3 μm, shape factor of 0.78 were obtained when the raw C3771 lead brass were rotary swaged to a radial strain of 0.22 and then heated to 895 °C for 5 min. The Forge 3D software was used to analyze the temperature, strain and strain rate distribution of copper valve for obtain the reasonable process parameters during the subsequent rheoforging process. The experiment results showed that near-spherical micro-grains were stretched and refined to about 35.7-43.4 μm in different positions due to the dynamic recrystallization during the rheoforging process. The cap thread and nut thread failure torque of the so-produced valve are also discovered to be higher than the traditionally forged copper valve with dendrite micro-grains, with an enhancement of the cap and thread failure torque of 42.2 % and 28 %, respectively.

Key words: Semi-solid, Microstructural evolution, Dynamic recrystallization, Mechanical properties

Miao Cao, Qi Zhang, Ke Huang, Xinjian Wang, Botao Chang, Lei Cai. Microstructural evolution and deformation behavior of copper alloy during rheoforging process[J]. J. Mater. Sci. Technol., 2020, 42: 17-27.

Figures/Tables 21

Fig. 1. Two-dimensional drawing of valve.

Fig. 2. RS machine produced by Xi’an Innovation Precision Instrument Research Institute.

Fig. 3. Rheoforging process flow of copper valve.

Fig. 4. 35 tons hydraulic extruder.

Fig. 5. Cap thread and nut thread.

Fig. 6. Liquid fraction of rotary swaged C3771 alloy: (a) DSC vs. temperature curve; (b) liquid fraction vs. temperature curve.

Fig. 7. True stress-strain curves of RSSIMA-processed C3771 at 900 °C.

Fig. 8. Geometry of the rheoforging die.

Fig. 9. Metal flow in rheoforging process.

Fig. 10. Simulation results in the last simulation step at rheoforging temperature at 900 °C with the rheoforging speed of 30 mm/s and the die temperature of 300 °C: (a) temperature distribution of copper valve; (b) equivalent strain distribution of copper valve; (c) strain rate distribution of copper valve.

Fig. 11. Temperature distribution of copper valve in the last simulation step at rheoforging temperature at 900 °C, the speed of 20 mm/s and the die temperature of 300 °C.

Fig. 12. Temperature change with rheoforging timee of the tracking pionts: (a) 30 mm/s; (b) 20 mm/s.

Fig. 13. Forging force variation with the calculation step during the rheoforging process.

Fig. 14. Temperature field distributions at different rheoforging temperatures of semi-solid billet: (a) 895 °C; (b) 890 °C.

Fig. 15. Microstructures of C3771 copper alloy: (a) as-cast; (b) rotary swaged.

Fig. 16. Rotary swaged C3771 microstructures at different IHT conditions: (a) 890 °C holding for 5 min; (b) 895 °C holding for 5 min; (c) 900 °C holding for 5 min; (d) 900 °C holding for 10 min.

Fig. 17. (a) Semi-finished rheoforged valve and (b) finished rheoforged valve.

Fig. 18. (a) Sampling position in rheoforging valve, (b) microstructure of IHT copper alloy with a radial strain value of 0.3 at 895 °C holding for 6 min and microstructures in rheoforging valve for (c) sampling position a, (d) sampling position b and (e) sampling position c.

Table 1 Cap thread and nut thread failure torque of semi-solid copper valve.

Number	1	2	3	4	5
Cap thread damage torque (N m)	50	52	62	65	59
Nut thread breaking torque (N m)	55	56	53	55	55

Table 2 Cap thread and nut thread failure torque of traditionally forged copper valve.

Number	1	2	3	4	5
Cap thread damage torque (N m)	37.5	35	44	40	46
Nut thread breaking torque (N m)	47	45	43	42	37

Fig. 19. Vickers hardness of semi-solid forged valve and conventional forged valve.

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