Effect of Magnesium on Microstructure Refinements and Properties Enhancements in High-Strength CuNiSi Alloys

doi:10.1007/s40195-019-00953-9

Abstract

Abstract:

Microalloying is an effective method to improve the comprehensive properties of copper alloys. The effects of magnesium on the microstructure, mechanical properties and anti-stress relaxation properties of CuNiSi alloys have been investigated. Results demonstrated that magnesium plays significant roles in refining the dendritic microstructure of the as-cast ingot, accelerating the precipitation decomposition, improving the mechanical properties and increasing the anti-stress relaxation properties. The incremental strength increase is due to the Orowan strengthening from the nanoscale Ni₂Si and Ni₃Al precipitates. As compared with the Cu-6.0Ni-1.0Si-0.5Al (wt%) alloy, the ultimate tensile strength of the designed Cu-6.0Ni-1.0Si-0.5Al-0.15Mg (wt%) alloy increases from 983.9 to 1095.7 MPa, and the electrical conductivity decreases from 27.1 to 26.6% IACS, respectively. The stress relaxation rates of the designed Cu-6.0Ni-1.0Si-0.5Al-0.15Mg alloy are 4.05% at 25 °C, 6.62% at 100 °C and 9.74% at 200 °C after having been loaded for 100 h, respectively. Magnesium significantly promotes nucleation during precipitation and maintains small precipitate size.

Key words: Copper alloy, Precipitation, Aging, Mg addition, Strength, Stress relaxation

Tao Xiao, Xiao-Fei Sheng, Qian Lei, Jia-Lun Zhu, Sheng-Yao Li, Ze-Ru Liu, Zhou Li. Effect of Magnesium on Microstructure Refinements and Properties Enhancements in High-Strength CuNiSi Alloys[J]. Acta Metallurgica Sinica (English Letters), 2020, 33(3): 375-384.

Figures/Tables 10

Table 1 Chemical composition of the studied alloys (wt%)

Fig. 1 Optical micrographs of the dendritic microstructure in the as-cast studied alloys. a Cu-8.0Ni-1.8Si; b Cu-8.0Ni-1.8Si-0.15Mg; c Cu-6.0Ni-1.0Si-0.5Al; d Cu-6.0Ni-1.0Si-0.5Al-0.15Mg

Fig. 2 Optical micrographs of the solid solution-treated studied alloys. a Cu-8.0Ni-1.8Si; b Cu-8.0Ni-1.8Si-0.15Mg; c Cu-6.0Ni-1.0Si-0.5Al; d Cu-6.0Ni-1.0Si-0.5Al-0.15Mg

Fig. 3 Properties of the solid solution-treated studied alloys aged at 450 °C for various durations. a Vickers hardness; b electrical conductivity

Fig. 4 Stress-strain curves and fractures of the studied alloys. a Stress-strain curves of Cu-8.0Ni-1.8Si and Cu-8.0Ni-1.8Si-0.15Mg alloys; b fracture of Cu-8.0Ni-1.8Si alloy tensile tested sample; c fracture of Cu-8.0Ni-1.8Si-0.15Mg alloy tensile tested sample; d stress-strain curves of Cu-6.0Ni-1.0Si-0.5Al and Cu-6.0Ni-1.0Si-0.5Al-0.15Mg alloys; e fracture of Cu-6.0Ni-1.0Si-0.5Al alloy tensile tested sample; f fracture of Cu-6.0Ni-1.0Si-0.5Al-0.15Mg alloy tensile tested sample

Table 2 Physical properties of the studied alloys

Fig. 5 Bright-field micrographs of microstructural evolutions in Cu-8.0Ni-1.8Si-(0.15Mg) alloys having been aged at 450 °C for various durations. Cu-8.0Ni-1.8Si alloy: a 15 min; b 60 min; c 300 min. Cu-8.0Ni-1.8Si-0.15Mg alloy: d 15 min; e 60 min; f 300 min

Fig. 6 Bright-field micrographs of microstructural evolutions in Cu-6.0Ni-1.0Si-0.5Al-(0.15Mg) alloys having been aged at 450 °C for various durations. Cu-6.0Ni-1.0Si-0.5Al: a 5 min; b 60 min; c 120 min. Cu-6.0Ni-1.0Si-0.5Al-0.15Mg: d 5 min; e 60 min; f 120 min

Fig. 7 Stress relaxation rate of the studied alloys stress loaded at different temperatures for various durations. a Cu-8.0Ni-1.8Si; b Cu-8.0Ni-1.8Si-0.15Mg; c Cu-6.0Ni-1.0Si-0.5Al; d Cu-6.0Ni-1.0Si-0.5Al-0.15Mg

Fig. 8 Bright-field micrographs of microstructural evolutions in Cu-6.0Ni-1.0Si-0.5Al-0.15Mg alloy samples loaded at different temperatures for different time. a 25 °C/2 h; b 25 °C/20 h; c 25 °C/100 h; d 200 °C/2 h; e 200 °C/20 h; f 200 °C/100 h

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