Processing of magnesium based in-situ metal matrix composites

Abstract

Magnesium matrix composites having combination of their indispensable and superior properties has drawn an outstanding attention for various implementations especially in automotive and aerospace industries. The main objective of the present study was to develop a furnace and a set-up for the synthesis of Mg composites by in-situ reactive infiltration process and finally synthesis of in-situ composites and characterize the composites synthesized. A vertical furnace, an inert perplex chamber for powder mixing and an inert stainless steel chamber for preform infiltration were manufactured in the laboratory using locally available materials. Magnesium matrix in-situ composites were synthesized using commercially pure Mg and Mg alloy ingot, coarse Ti and B4C powder. Ti and B4C powders were taken with zirconia balls in a plastic bottle in Ar atmosphere and mixed by ball milling. The resulting mixture of these powders were compacted into a cylindrical preform. The Ti-B4C preforms were infiltrated with pure Mg and Mg based alloy by capillary forces under Ar atmosphere in the newly fabricated or build electric resistance furnace at temperatures of 800oC and 900oC for different holding time. Then the samples were prepared for phase identification and microstructural investigation. Microstructure of all Mg based in-situ composites were investigated with an optical microscope and a field emission scanning electron microscope (FESEM). The phases formed during infiltration were analyzed using X-ray diffraction technique with Cu K radiation and morphology of the structure was investigated using FESEM equipped with Energy dispersive X-ray (EDX). Differential Thermal Analysis (DTA) was used to determine the solidus, liquidus melting temperature and solidification range of the Mg in-situ composites. To determine the mechanical properties, Brinell hardness tests were carried out. Relative density and porosity of the in-situ composites were also measured. In addition, the parametric studies revealed that the processing conditions such as temperature, holding time and green compact relative density had influenced significantly the in-situ reaction and the fabrication of the in-situ composites. It was observed from the SEM and EDX investigation that the Ti particles dissolution increased with increasing infiltration temperature and time. XRD study revealed that TiC, TiB2, TiB, MgB2, MgB4 and B13C2 compounds were formed during infiltration in Mg in-situ composites. A new compound Ti2AlC was found to form in Mg alloy in-situ composites. The presence of Ti, B4C and intermediate compounds TiB, MgB2, MgB4 and B13C2 in the in-situ composites indicated that the reactions were incomplete. The bulk density of pure Mg and Mg alloy in-situ composites was found to change with the increase of infiltration temperature and time. The melting temperature and the solidification range of the Mg based in-situ composites were observed to change with the processing temperature and time. No significant trend of the effect of processing parameters on the change of hardness was observed.