超声波作用下SiCp/Al复合材料焊缝的凝固组织及其断裂特征

摘要

The microstructural characteristics of ultrasonic assisted fabricating bonds in SiCp/Al composites were investigated and the in­situ dynamic tensile process and the fracture surface at room temperature of the resultant bonds were observed by scanning electric microscopy (SEM). The results show that the bond microstructure can be effectively controlled by the application of ultrasonic vibration at different bonding stages. All the bonds rupture instantaneously under the tensile stress before obvious cracks are observed, which belong to a brittle fracture mode. When the bond is free of SiC particles, the flourishing Zn­Al eutectics are weak and serve as the crack sources and the main path of crack propagation. When SiC particles are present in the bond, which are transferred from the base metal and agglomerate in the Zn­Al eutectics, micro­crack initiates at the SiC/eutectics interface and mainly propagates along the Zn­Al eutectics, with a number of cleavage fracture of primary phase β(Zn) occurring in the crack propagation path under the rupture inertia. Primary phaseα(Al) has a significant role in crack resistance.%　　研究超声波作用下SiCp/Al复合材料焊缝的微观组织特征，并采用SEM对室温下焊缝的原位拉伸断裂特性过程及断口形貌进行观察分析。结果表明，在焊接不同阶段经超声波处理，可有效地控制焊缝的微观组织。在拉伸应力作用下所有焊缝在没有观察到明显裂纹生成之前瞬间发生断裂，呈现脆性断裂的特征。当焊缝中无 SiC颗粒时，焊缝中发达的Zn­Al共晶相为焊缝的薄弱相，是裂纹萌生的部位，且是裂纹扩展的主要路径。当母材中的SiC颗粒迁移到焊缝中时，主要聚集于共晶相中，SiC颗粒和共晶组织的结合界面是微裂纹萌生的部位，裂纹主要沿着共晶组织扩展，在强大的脆性断裂惯性作用下，扩展路径上较多的先共晶相β(Zn)发生解理断裂，先共晶相α(Al)具有明显的抗裂作用。