Selected the Casting Properties of the Composites AlMg10+Cgr

Abstract

The paper is a review of the previous investigations concerning the influence of graphite particles both on the casting properties of metal matrix composites (MMCs). The work presents the examination results of casting properties (i.e. castability and shrinkage) of the MMCs with matrices of a selected aluminium alloy reinforced with graphite particles. There is also presented the influence of graphite particles on the surface tension and viscosity of the flowing and filling the mould composite suspension. The suspensions containing various percentages of graphite particles (namely 5%, 10%, or 15% in volume) were prepared in order to perform the above mentioned examinations. Castability (fluidity) of these suspensions was measured in two ways, i.e. by means of both the spiral test and the rod test, while their shrinkage was determined with the use of a device designed and assembled in the Department of Foundry Engineering, CUT. The device enables to determine changes in the length of a casting during its solidification with respect to the specified length of the test rod. The surface tension was determined by the wedge casting method consisting in the pouring of metal into an open shell mould with the cavity of wedge geometry, the sharp edge being perpendicular to the free metal surface. The change in viscosity corresponding to the change in graphite particles percentage was calculated from Einstein’s equation. The results of examinations show that the introduction of reinforcing graphite particles results in both a significant increase in the viscosity of the flowing suspension and a considerable decrease in its castability. The greater dimensional stability of castings was observed, i.e. the shrinkage of composite castings was smaller than the shrinkage of matrix alloy itself. An increase in surface tension index value with an increase in volume percentage of graphite particles in composite was also noticed.

Keywords

• aluminium alloys
• metal composites
• graphite particles
• castability
• surface tension