Cast and age hardening behaviour of Al6061 alloy reinforced with an in-situ ceramic composite prepared by carbo thermal reduction of fly ash in plasma reactor

Abstract

An in-situ ternary ceramic composite material is developed indigenously by carbo thermal reduction of fly ash in a plasma reactor. X-ray diffraction (XRD), Scanning electron microscopy (SEM)-Energy dispersive x-ray (EDX) analyses of the developed ternary mixture has revealed in-situ conversion of SiO2 to SiC in the vicinity of Al2O3, present in the fly ash material. Presence of carbon in the form of graphite is also confirmed by XRD and EDX analyses. The morphology of the fly ash powder particles is changed from irregular to rod shaped particles with the presence of whiskers (diameter approximate to 0.2 mu m, length 8-20 mu m). Metal matrix based (Al6061) ceramic composites are prepared with the plasma synthesized fly ash and untreated fly ash composites by stir casting method with different volume fractions of ceramic powders of both the category. Progressive reductions of grain size by increasing volume fractions with segregation of ceramic particles at the grain boundaries are salient features of microstructures. Remarkable improvement in strength and wear resistance is the two significant features of the novel Al6061alloy based composite developed with plasma treated fly ash. Results are presented on the ageing behaviour of the alloy composite for both the categories and mechanical properties of age hardened alloy based composites are compared with monolithic alloy. Accelerated ageing behaviour is observed for alloy based composites, which is found to depend on the morphology of the incoherent dispersed phases. Accelerated precipitation during ageing has been confirmed by hardness versus time as well as by differential scanning calorimetry analysis. Sequences of precipitation for all materials are shown in differential scanning calorimetry thermogram.