Wetting improvement of carbon or silicon carbide by aluminium alloys based on a K2ZrF6 surface treatment: application to composite material casting

Abstract

A surface treatment with aqueous solutions of K2ZrF6 has been carried out to improve, in dramatic manner, the wetting of carbon (or SiC)-base ceramics by liquid light alloys at low temperatures (i.e. within the 700 to 900°C range). The mechanism which is thought to be responsible for the wetting improvement involves two steps: (i) K2ZrF6 reacts with aluminium with the formation of K3AlF6, other complex fluoride species and intermetallics, (ii) K3AlF6 dissolves the alumina thin layer, coating the liquid light alloy and enables the wetting of the ceramics. The mechanism has been worked out from sessile drop experiments, solid state chemistry experiments and composite casting. The K2ZrF6 surface treatment appears to be particularly suitable for processing composite materials made of carbon (or SiC) fibrous preforms and aluminium-base matrices according to techniques directly derived from the light alloy foundry.