Research On The Fabrication Of In-Situ Aluminun Based Composites By Electroslag Remelting (ESR) Process

A novel technique for preparation of in-situ Al based composites by electroslag remelting (ESR) process has been studied in this paper. The feasibility of in-situ synthesis of TiB2/Al and Al₃Ti/Al composites by ESR process was verified by investigating the microstructure and phases of the composites. Scanning electron microscope(SEM), X-ray diffraction(XRD),Energy Disperse Spectroscopy(EDS) were used to analyze the phase of composites and slag skin and also observe the microstructures of the composites.The effects of the ESR process were systematically studied especially the fluxes composition and the electricity parameters such as the remelting voltage and current.The stability and uniformity for the ESR in-situ reaction were examined and the mechanism of the ESR influences on the in-situ synthesis was probed. The hardness and tensile property were also tested to make sure the reinforcements took effects.The experiments results showed that combination of fluoride salts and the basic fluxs including KCl,NaCl and Na₃AlF₆ were suitable to set up slag pool and supplied heat to melt the electrode.Howere,only the fluoride salts were not good as the ESR slag since they were easily to be oxidized.The TiB2 and Al₃Ti particulates distributed uniformly in the aluminum matrix with much smaller size compared with the conventional casting method. There were mainly three morphologies for Al₃Ti such as blocky,needle-like and flaky particulates with different aspect ratio,which was determined by the Ti concentration and solidification speed, etc.The remelting time decreased while the temperature of the slat pool enhanced with the increase of the remelting current.The electricity system was carefully studied to find the best parameters and good quality TiB2/Al composites ignot could be obtained when the remelting current was 600A with the voltage 15V. The unstability and unsustainability existed during the ESR process since the Ti atom was consumed as the in-situ reaction proceeded so that the Al₃Ti particulates amount decreased from under part to the upper part of the composites ignot.The ESR process was able to increases the molten aluminum surface area in contact with fluoride salts by the contact of end of electrode,aluminum drops,metal molten pool with the slag pool full with fluoride salts.Besides,the electromagnetic and electrodynamic force generated by the ESR system could lead to the movement of slag pool,which definitely updated the slag-metal interface and improved the reaction efficiency.The results of property evaluation of TiB2/Al and Al₃Ti/Al composites showed that the hardness, tensile strength and yield strength enhanced with the increase of the reinforcements while the specific elongation was reduced compared with the pure aluminum.The matrix aluminum grain was refined by the TiB₂ and Al₃Ti,which played important role in improving the strength.However,the comprehensive mechanical properties were not as good as the composites produced by traditional mixed salt reaction process because the slag may enter into the composites.The fracture morphology appeared as ductile fracture as there were many dimples together with few brittle cleavage plane.