Yb和Si对Al-Zr合金析出行为的影响及作用机制

EFFECT OF Si AND Yb ON PRECIPITATION BEHAVIOR OF Al-Zr ALLOYS DURING AGING

采用显微硬度、电导率测试、扫描电镜及三维原子探针等测试手段研究了Al-ZrYb、Al-Zr-Si和Al-Zr-Si-Yb合金的时效析出行为以及Yb和Si的作用机制。结果表明,同时添加Yb和Si能明显提高Al-Zr合金的析出强化性能,两者均可加速Al-Zr合金时效析出,但作用机制不同。时效初期Yb在α-Al中优先扩散,形成Al_3Yb作为Zr析出的异质核心,加速Zr的析出,形成核壳结构的复合析出相Al_3(Zr_(1-x)Yb_x)。Si可以提高Zr在Al基体中的扩散速率,因此添加Si后合金中Al_3Zr的时效析出孕育期缩短,析出相长大速率增大,但同时合金抗粗化能力下降。此外,Si的加入大大降低了Yb在Al基体中的固溶度。因此尽管Yb仍然倾向于偏聚在析出相中心,但原子分数仅约1%,Zr在析出相中几乎均匀分布,Si在基体/析出相界面处略有偏聚,析出相(Al,Si)_3(Zr_(1-x)Yb_x)总体上不呈现核壳结构。

Effects of Yb,Si additions to Al-Zr alloys were investigated to study hightemperature aging properties and precipitation behaviors. Measurements involving Vickers microhardness,electrical conductivity,scanning electron microscope（ SEM） and three dimensional atom probe（ 3 DAP） were employed to demonstrate precipitation behavior of Al-Zr-Yb,Al-Zr-Si and Al-ZrSi-Yb,and mechanism of Si and Yb. Result confirmed that both Yb and Si accelerated aging precipitation in Al-Zr alloys with different mechanisms. Al-Zr-Yb presented Yb-core / Zr-shell structure in Al_3（ Zr_（1-x）Yb_x） precipitates,in which Yb dispersed preferentially into Al_3Yb,acting as heterogeneous nuclei for Zr. Small Si addition evidently accelerated precipitation by enhancing Zr diffusion rate in Al-matrix. Thus, the incubation period of Al_3Zr precipitates was shortened;meanwhile coarsening resistance of the alloy was decreased. Besides,Si addition largely decreased solubility of Yb in Al-matrix,leading to an order of magnitude lower than that of ternary alloys.Therefore,despite that Yb presented segregation at the core,it had much lower concentration of1 at%. Zr distributed evenly in the Al-matrix while Si showed segregation at the interface of precipitateand Al-matrix. There was no obvious core / shell structure in（ Al,Si）_3（ Zr_（1-x）Yb_x）.