Improvement of particle-reinforced composites by metal forming aided by cyclic shear stress

There are numerous defects that can be found in cast metal composites, such as pores, voids as well as nonhomogenous location, sedimentation and agglomeration of homophase and hetherophase reinforcement particles in a matrix of composite. Moreover, weak wetting of ceramic particles by liquid matrix material is the additional factor that contributes to worsening of properties of composite manufactured by classical casting processes. The paper presents a new method for altering the microstructure of cast composites reinforced with different kind of ceramic particles. The method consists in compression aided by additional shear stress caused by transverse motion of a punch. As the result, severe plastic deformation is possible without heat treatment between subsequent steps of plastic deformation. A series of experiments was conducted for previously casted Al-Mg-Cu matrix composites with three reinforcement variations. Silicon carbide particles, glassy carbon particles and the mixture of SiC particles and glassy carbon particles were used as the reinforcement. The mass percentage of reinforcement in every kind of composite was set to 15 wt%. It was found that the applied method allowed to eliminate the microstructure defects of initial as-cast microstructure. In addition, it enabled to refine the particles to the ultra-dispersed size with a good-quality conjunction on the particle-matrix interface and, in consequence to improve mechanical properties of the investigated composites.