Understanding the relationship between microstructure and mechanical properties of Al–Cu–Si ultrafine eutectic composites

Abstract

Systematic investigations for the influence of the microstructural change derived from compositional tuning in Al-rich corner of Al–Cu–Si system on mechanical properties demonstrate that mechanical characteristic of ultrafine eutectic composites strongly depend on the crystallinity, length scale and volume fraction of constituent phases. Ultrafine eutectic composites can be divided into two categories: 1) whether primary phases exist or not and 2) the types of matrix phases, i.e., single eutectic or bimodal eutectic. The features of primary phases play a principal role on the macroscopic property. Ductile α-Al phase is very effective to improve the plasticity while brittle Al2Cu intermetallic phase deteriorates obviously mechanical performance. In addition, bimodal eutectic matrix alloys composed of eutectics with different length scale and morphology show superior mechanical properties than single eutectic matrix alloys. Based on the microstructural studies, it is believed that high strength is originated from ultrafine scale microstructure and enhanced plasticity is supported by strain gradient plasticity. These results reveal that mechanical properties of the ultrafine eutectic composites can be properly optimized via control of chemical and topological governing factors.