Structure and microhardness of aluminum matrix composite produced by severe plastic deformation

Abstract

The influence of various schemes and modes of deformation on the distribution pattern of reinforcing SiC particles in an aluminum matrix is considered in the work. The severe plastic deformation methods such as high pressure torsion (HPT) and friction stir processing (FSP) were used for research. By means of HPT, chips of pure aluminum and powder of SiC (after ball milling) were consolidated on Bridgman anvils with 12 mm diameter and 0.25 mm depth grooves, at a pressure of 5GPa, 30 revolutions and a strain rate ω=2 rpm. By this way, samples of aluminum matrix composite (AMC) were obtained. In the case of FSP, SiC powder was introduced into AK4-1 (equivalent of the alloy 2618) aluminum alloy. The FSP was conducted with the rotational and traveling speeds of 1000 rpm and 30 mm/min, respectively. The shear deformation during the HPT process was sufficient for the fragmentation of initial SiC particles, but not sufficient to distribute uniformly the fragments in the aluminum matrix. Therefore, initial conglomerates of SiC particles and single fragmented SiC particles were observed. The deformation during FSP was sufficient to fragmentation of initial SiC particles and evenly distribute them in the aluminum matrix to obtain a homogeneous ACM structure, but insufficient to produce a defect-free AMC. The microhardness measured of the obtained aluminum matrix composites changed nonmonotonically and depended on the distribution of SiC particles.