超高强CuNiSiMg系合金的相变及其对合金抗应力松弛性能的影响规律

The beryllium-free elastic copper alloys with super-high strength, excellent stress relaxation resistance and good electric conductivity are widely used to manufacture the environmental-friendly relays， which could bear high load and persist much longer time work. We have successfully developed a beryllium-free CuNiSiMg alloys with super-high strength, excellent stress relaxation resistance and good electric conductivity. However, the phase transformation behavior(especially in the early stage of aging)and the effect of phase transformation behavior on stress relaxation resistance in CuNiSiMg alloys dring aging have not been investiagted systematically yet. Three dimensional atom probe (3DAP) and high resolution electron microscopy will be used to investigate the interactions between the solute atom and vacancy and among the solute atoms themselves in the alloy during aging, and to reveal the existing form of micro-alloying elements in the alloy,the effect of micro-alloying elements on precipitating process during aging and structure evolution under normal working condition. In order to discover the mechanism of the excellent anti-stress relaxation properties of CuNiSiMg alloys，the precipitation behavior and the characteristic of precipitates of the alloy (including the characteristic of 'Mg atoms phere',the precipitate size,composition,structure,diffusion and distribution，and orientation relation between precipitates and matrix) during aging, and the interactions between the precipitates (including 'Mg atoms phere' ) and dislocations will be studied with crystallography analysis, thermodynamic and kinetic analysis of phase transformation. A new theory will be established to help developping the novel environmental-friendly elastic copper alloys as substitutes for toxic Cu-Be alloys from this study.

超高强、高抗应力松弛、无铍的导电弹性铜合金是航空、航天、民用电子等工业用高负载、高服役寿命的绿色环保型继电器等的关键材料之一。前期预研中我们成功研制出一种无铍且具有超高强、高抗应力松弛和良好导电性能的CuNiSiMg系合金，但对该合金时效相变规律（特别是时效早期相变规律）及其对合金抗应力松弛性能的影响尚缺乏系统研究。本项目拟采用三维原子探针和高分辨电子显微镜等手段，从原子层面上研究合金时效过程中溶质原子间以及溶质原子与空位间的相互作用，揭示微合金化元素在合金中的存在形式及其对合金的沉淀析出行为和服役过程中组织演变的影响规律；从晶体学结构、相变热力学及动力学的角度分析合金的析出行为和析出相特征（包括镁原子"气团"的特征，析出相大小、成分、结构、位向、弥散度和分布等）及其与位错的相互作用机制，探明合金具有高抗应力松弛性能的机理。通过研究将为替代毒性铍青铜的环保型铜合金开发奠定基础。

本项目对超高强弹性CuNiSiAlMg合金的成分设计、形变热处理、加工工艺参数、时效初期原子分布、沉淀相变行为、析出惯序、高温应力松弛行为等进行了系统的研究和分析，得到的主要结果及相关数据如下：（1）合金的铸锭组织呈树枝状结构，枝晶骨架主要为α-Cu相，第二相粒子主要为Ni2Si相、Ni3Si（Ni74Si26）和Ni3Al相。Al、Mg、Cr元素则均匀地分布在基体中。（2）合金高温压缩变形具有动态再结晶特征，可分为加工硬化、回复和动态再结晶三个阶段，合金适宜的热加工温度范围为850℃~900℃。热变形织构低温下主要为立方织构{001}<100>，高温下主要为Copper织构{112} <111>和 Gauss织构{011} <100>。（3）合金经优化单级时效处理后获得的性能为：硬度341HV，电导率26.5%IACS，抗拉强度1090 MPa，屈服强度 940 MPa，伸长率 3.5%。合金在450℃时效具有很好的抗过时效能力，即使时效20小时后硬度值仍有330.1HV。峰时效态合金在室温、100℃和200℃下加载100小时后的应力松弛率分别为4.05%、6.52%和9.74%。组合时效后有利于合金获得良好的综合性能，硬度372HV，抗拉强度1143MPa，屈服强度1072MPa，电导率26.7%IACS。（4）合金过饱和固溶体时效相变贯序为：过饱和固溶体→团簇→L12有序化（Ni3Si）→β-Ni3Si相→β-Ni3Si相+δ-Ni2Si相。在450℃时效5min后即发生沉淀析出，析出相尺寸约为3~4nm；时效60min后，析出相为β-Ni3Si和δ-Ni2Si相；时效480min后，出现了δ’-Ni2Si相，尺寸为13~15nm。500-550℃时效处理一定时间出现了条带状的不连续胞状析出。600℃时效60min后，δ-Ni2Si分布上出现了存在不同方向的变体。650-800℃时效长时间后析出相长大明显，可达250 nm。（5）固溶处理后，合金的各元素均匀地分布在基体中。时效早期，Al有在界面富集的趋势，其富集阻碍了团簇粒子的长大，使的析出相粒子较细小，提高了合金的应力松弛性能。不论添加Mg与否，冷轧均使时效硬度峰提前；添加Mg的合金时效硬度峰相对滞后，时效峰宽加大。