Optimisation of mechanical milling process for production of AA 7075/(SiC or TiB 2 ) composite powders

The present work concerns the processing of composite powders based on 7075 aluminium alloy by mechanical milling. A premixed powder (Alumix 431D, Ecka Granules, Germany) was used as the matrix material, and two different ceramic reinforcements (SiC and TiB₂) were chosen as reinforcements. The main objective was to evaluate the effect of the content and addition method of the process control agent as well as the content and type of reinforcement on the microstructural and morphological evolutions of the powder particles during milling process and the as milled properties of the processed materials. Results showed that regardless of the starting composition, alloying took place through three stages, in which deformation, cold welding and fracturing of powder particles were the main mechanisms involved respectively. The mechanically milled composite powders showed a fine and homogenous distribution of reinforcement particles. A higher content of reinforcement resulted in a lower crystalline size for the milled powders (∼18 nm for composite powders containing 15 vol.-% ceramic particles).