粉末冶金泡沫Al-Si-Cu发泡过程的微观结构演变

Microstructure Evolution in Powder Metallurgy Al-Si-Cu Foam during Foaming Process

摘要:

本文采用扫描电镜和能谱分析了泡沫Al-Si-Cu合金发泡过程的微观结构演变。将Al粉、Cu粉、Si粉按照89:6:5比例（wt%）混粉，并添加发泡剂2 wt % TiH2和增稠剂1.5 wt % MnO2，经过500℃热压后，泡沫铝可在640℃/12-20min发泡。微观结构分析显示，发泡前泡沫铝呈现球形的Si、Al2Cu、块状TiH2和扁片MnO2相，发泡后泡沫铝孔壁内存在三类析出相：1. 晶内细小的Si、Al2Cu颗粒；2. 晶界粗大离异共晶Si、Al2Cu相；3. 随机分布的块状Al-Mn相、MnO2相和球形富Ti相。其中富Ti相是由TiH2分解H2后，与铝液反应产生的，具有两种不同的类型。两类析出相心部都为Ti颗粒，第一类内壳为τ2(Al14Ti33Si53)相薄层，外壳呈现枝晶形貌的τ1(Al20Ti32Si48)和τ2相；第二类外部为块状交替分布的τ1和(Al,Si)3Ti相。第一类富Ti相的Si成分明显高于第二类，可能是两类富Ti相分别形成于铝液中的富Si和贫Si区造成的。对泡沫铝发泡过程微观结构的分析有助于设计高性能可强化的泡沫铝。

Abstract:

The microstructure evolution in Al-Si-Cu foam during foaming process was studied using the scanning electron microscope. Through mixing the powder to the composition of Al-6Si-5Cu-2TiH₂-1.5MnO₂ wt%, and using the hot pressure process at 500℃, the Al foam could be foamed homogeneously at 640℃ for 12-20min. The corresponding microstructure analysis showed that the sample before foaming contained spherical Si, Al₂Cu, lump-shaped TiH₂ and flat MnO₂ phase. After foaming, the sample showed the millimeter-scale main hole with the sparse micrometer-scale pores inside the hole wall. The precipitates in hole wall were intragrain small Si and Al₂Cu particles, and grain boundary eutectic Si and Al₂Cu phases, as well as randomly distributed lump-like Al-Mn phase, MnO₂ phase and spherical Ti-rich phase. Therein, the Ti-rich phase, formed by the reaction of liquid Al and TiH₂ after release H₂, exhibited two types of morphology. The first one consisted of a Ti core, a thin layer of τ₂(Al₁₄Ti₃₃Si₅₃) inner shell, and the mixed dendrite-like τ₁(Al₂₀Ti₃₂Si₄₈) and τ₂ phases outer shell. The second type of morphology consisted of Ti core, and a mixed lump-like τ₁and (Al,Si)₃Ti shell. The composition of Si in the first type was much higher than that of the second type. That was mainly because the Si composition in liquid Al was not uniform due to the inheritance of the original microstructure of solid Al and Si, and the two types of Ti-rich phase formed in the Si rich and Si poor regions. The microstructure analysis of foaming process could be the foundation for designing the aging strengthening aluminum foam.