THE CONTROL OF GRAIN-SIZE AND DISTRIBUTION OF PARTICLES IN A (6061-ALLOY)(M) (AL2O3)(P) COMPOSITE BY SOLUTIONIZING TREATMENT/

The grain growth during an isothermal treatment at a solutionizing tem perature of 540 degrees C has been studied in a composite containing 6 061 aluminum alloy matrix with Al2O3 particles. The grain growth law i s generally applicable to the composites containing 0.10, 0.15, and 0. 20 volume fraction of the Al2O3 particles (VFAP). It has been observed that the grain growth process involves the disintegration of the aggl omerated particles first and then particles coalesce at longer solutio nizing times in the composite containing 0.20 VFAP. The process of coa lescence has not been observed up to a heating time of 20 hours at thi s temperature in the composites containing 0.10 and 0.15 VFAP. The tra nsmission electron microscopy (TEM) study indicates the generation of a large number of dislocations in both the matrix and the area adjacen t to the particles. The dislocation densities at these two locations i n the composites increase with an increase in VFAP and the particle si ze. The microhardness measurements confirm the microstructural observa tions, and the hardness values for the composite and the matrix appear to be more sensitive to the particle distribution and the particle si ze compared to the grain size.