Effect of Magnesium Microalloying on Microstructural Strengthening and Mechanical Properties of Beryllium Bronze

Abstract

To address the critical bottlenecks of traditional beryllium bronze, such as poor strength-ductility synergy and susceptibility to high-temperature softening caused by its reliance on a single precipitation strengthening mechanism, a 0.08% Mg micro-alloying modification strategy is proposed in this study. By systematically investigating the effects of aging treatments on the microstructure, as well as the room-temperature and medium-to-high-temperature mechanical properties of the Mg-containing beryllium bronze, the strengthening role of Mg and the underlying mechanisms for microstructural stabilization are thoroughly revealed. The results indicate that the introduction of trace amounts of Mg yields a significant grain refinement effect, reducing the average grain size of the alloy from 25~40 μm to 15~25 μm. The Mg atoms exhibit a globally uniform solid solution state without grain boundary segregation. Without interfering with the normal nucleation of the γ'-Be₂Cu precipitates, a ternary synergistic strengthening system comprising "grain refinement, solid solution, and precipitation" is successfully established. Regarding the room-temperature mechanical properties, after a peak aging treatment at 330 °C for 2 h, the tensile strength of the alloy reaches 1211 MPa, while the elongation is robustly maintained at 8.98%. This strength-ductility synergy is significantly superior to that of traditional Mg-free beryllium bronzes. In terms of medium-to-high-temperature performance, tests demonstrate that after holding at 300 °C for 15 min, the tensile strength remains as high as 1119 MPa with an outstanding strength retention rate of 92.4%, exhibiting exceptional high-temperature thermal stability. Notably, when benchmarking the high-temperature performance against the commercial C17200 alloy, it is found that the uniformly dissolved Mg atoms kinetically suppress the coarsening rate of the strengthening precipitates through a strong "solute drag" effect. Within the core service temperature range of ≤300 °C, the microstructural stabilization efficacy provided by merely 0.08% of inexpensive Mg perfectly achieves functional equivalence to that of 0.2%~0.4% of costly and scarce strategic cobalt (Co). While significantly enhancing the comprehensive performance of beryllium bronze, this study provides a novel pathway to overcome the limitations of high-cost cobalt resources and to develop highly cost-effective, heat-resistant copper-beryllium alloys.