Effect of ball milling on densification and alloying in SiCp/Al powder metallurgy processes

Abstract

In this study, unprocessed raw Al, Cu, Mg powders, and SiC particles were mixed and subjected to high-energy ball milling (HEBM) to mitigate the negative effects of the oxide film on the quality of the pressureless sintering billets. Comparative experiments including pores and intermetallics examination were performed on both the mixed and HEBM powders across various preparation stages, including cold isostatic pressing, sintering, and hot extrusion of the 15vol.%SiC/Al-Cu-Mg. The pore structure and degree of alloying were analyzed using X-ray synchrotron radiation tomography. The results indicate that the brief HEBM process led to excellent mechanical properties in aluminum matrix composites after pressureless sintering and hot extrusion. The composites using ball-milled powder was relatively denser and complete alloying after sintering and extrusion, resulting in a density of up to 0.995 and a uniform distribution of Cu elements. The HEBM SiCp/Al had a tensile strength of 573 MPa and a fracture strain of 5.1 % which were higher than that of the mixed SiCp/Al. The results indicate that diffusion of alloy elements such as Cu was hindered by the interfaces between powders, led to Cu segregation and lower density of only 0.982 even after extrusion. Therefore, the composites using mixed powder had a lower tensile strength of 483 MPa and a fracture strain of 3.5 %. The study concluded that reducing the number and types of inter-particle interfaces could enhance the alloying and pore bridging processes.