粉末冶金泡沫Al-Si-Cu发泡过程的微观结构演变

Microstructure Evolution During Foaming of Al-Si-Cu Foam Produced by Powder Metallurgy Method

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(质量比)混粉,并添加发泡剂2%TiH_(2) (质量分数)和增稠剂1.5%MnO_(2) (质量分数),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、Al_(2)Cu、块状Ti H_(2)和扁片状Mn O_(2)相,发泡后泡沫铝孔壁内存在3类析出相:晶内细小的Si、Al_(2)Cu颗粒;晶界粗大离异共晶Si、Al_(2)Cu相;随机分布的块状Al-Mn相、MnO_(2)相和球形富Ti相。其中富Ti相是由Ti H_(2)分解H_(2)后,与铝液反应产生的,具有2种不同的类型。2类析出相心部都为Ti颗粒,第1类内壳为τ2(Al14Ti33Si53)相薄层,外壳呈现枝晶形貌的τ1(Al_(2)0Ti32Si48)和τ2相;第2类外部为块状交替分布的τ1和(Al, Si)3Ti相。第1类富Ti相的Si成分明显高于第2类,可能是2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。

The microstructure evolution in Al-Si-Cu foam during foaming process was studied by the scanning electron microscope. Through mixing the powder to the composition of Al-6 Si-5 Cu-2 TiH_(2)-1.5 MnO_(2)(wt%), and using the hot pressure process at 500 ℃, the Al foam could be foamed homogeneously at 640 ℃ for 12-20 min. The corresponding microstructure analysis shows that the sample before foaming contains spherical Si, Al_(2) Cu, lump-shaped Ti H_(2) and flat Mn O_(2) phase. After foaming, it shows that the millimeter-scale main hole with the sparse micrometer-scale pores inside the hole wall. The precipitates in hole wall are intragrain small Si and Al_(2) Cu particles, and grain boundary eutectic Si and Al_(2) Cu phases, as well as randomly distributed lump-like Al-Mn phase, MnO_(2) phase and spherical Ti-rich phase. Therein, the Ti-rich phase,formed by the reaction of liquid Al and TiH_(2) after releasing H_(2), exhibits two types of morphology. The first one consists of a Ti core, a thin layer of τ2(Al14 Ti33 Si53) inner shell, and the mixed dendrite-like τ1(Al_(2)0 Ti32 Si48) and τ2 phases outer shell. The second type of morphology consists of Ti core,and a mixed lump-like τ1 and(Al, Si)3 Ti shell. The composition of Si in the first type is much higher than that of the second type. That is mainly because the Si composition in liquid Al is not uniform due to the inheritance of the original microstructure of solid Al and Si, and the two types of Ti-rich phase form in the Si rich and Si poor regions. The microstructure analysis of foaming process can be the foundation for designing the aging strengthening aluminum foam.