For Pechiney/CRV (France): to identify the fundamentals of the elaboration of particulate reinforced aluminium matrix composites by the rheocasting route. For INTA (Spain): to measure and analyse the mechanical properties of the composites made at Pechiney. For Delft University (Netherlands): to acquire viscosity data on liquid or semi-liquid alloys or composites.
The objective of the project was to assess the potential of a compocasting route for making aluminium matrix composites and acquire a scientific knowledge of the rheology of the metallic slurry. A Couette viscosimeter was used to study the rheology of semiliquid metal and composites, as well as a micro compocasting pilot. The viscosity of fully liquid composites is about 50 to 300 times higher, depending on silicon carbide content, than that of the fully liquid matrix, but relatively low when compared to the partially solidified matrix. In both cases shear thinning properties were measured. As sudden changes of shear rates were imposed, a time dependency was observed, called thixotropy. Interaction between ceramic particles and solid phase coalescence in the semisolid aluminium alloy reduces the thixotropic tendency of the composite, by comparison with the semisolid alloy alone. A system has been developed for particle introduction into (semi) liquid metal based on a hollow rotor principle. Partial optimisation and upscaling of the system from 3kg up to a 50 scale have been carried out. 70mm diameter and 2 to 3 metre long billets of AS7G or 6061 aluminium alloy reinforced with 15% of 10 to 50um silicon carbide or alumina particulates were made, direct chill cast and extruded. The mechanical properties show encouraging levels.
THE MAIN OBJECTIVE OF THE RESEARCH PROJECT IS TO DEVELOP AL-MATRIX COMPOSITES REINFORCED WITH A DISCONTINOUS CERAMIC PHASE (SIC PARTICLES OR WHISKERS) WHICH CAN BE PRODUCED BY RHEOCASTING.
THE COMPOSITES SHOULD HAVE SPECIFIC STATIC MECHANICAL PROPERTIES FOR APPLICATIONS IN PARTS FOR WHICH WEIGHT SAVINGS, HIGH SPECIFIC MODULUS AND GOOD THERMAL PROPERTIES ARE REQUIRED.
COMPARABLE MMC'S HAVE ALREADY BEEN MADE BY SQUEEZE-CASTING BUT RHEOCASTING OFFERS A MORE FLEXIBLE AND CHEAPER ALTERNATIVE IF PROBLEMS OF SUFFICIENT VOLUME FRACTION OF CERAMIC REINFORCEMENT, OF WETTING AND OF EXTENDING THE PROCESS TO WHISKERS CAN BE SOLVED AND IF THE RESULTING MICROSTRUCTURE PROVES TO BE ADEQUATE.
Funding SchemeCSC - Cost-sharing contracts