Self-Propagating High-Temperature Synthesis And Characterization Of Al/Mg₂Si Compounds

Intetmetallic compound Mg₂Si is valued and researched as a new potential moderate and high temperature structural material as well as function material in aeronautics,astronautics and automotive etc.industry, because of low density, high melting point and high specific strength etc.But it is very difficult to process because of itsintrinsic brittleness at room temperature.So the research of improving the brittleness of Mg₂Si has a importance on theoretialside and practial application side.In this paper, a research on the weak exothermic reaction system of Al/Mg₂Si has been made from thermodynamics and structure dynamics.In ideal state the relationships of preperatue vs adiabatic temperature and quantity of Al vs adiabatic temperature were caculated. The results show that with the increasing of preheat temperature the adiabatic temperature of Al-Mg-Si system increases and reaches a flatform finally; with the increasing of quantity of Al the adiabatic temperature decreases, so does platform.The Al/Mg₂Si composite are synthesized by self-propagating combustion mode and thermal explosion mode respectively, between which a comparison of the reaction process has been made, and the different technical demands are definite. The effect of different technical parameters in preparation for Al/Mg₂Si composite during self-propagating combustion reaction mode on the phase compose and morphology of product has been studied, these parameters include mechanical-activation, preheat temperature, preheating velocity, pressure, Mg granularity and quantity of Al. on this basis, an optimal technical parameters scheme of combustion systhesis the Al/Mg₂Si composite has been summed up.A experiment of Combustion Front Quenching was brought to success in cylindrical steel mould by adding some Al-Ti-C powder, which is accepted high exothermic system on the top of Al-Mg-Si samples. The physical-chemical changes of all region in the quenched samples during the combustion systhesis were followed by XRD, SEM and EDS. The mechanism of synthesis Al/Mg₂Si composite could be described with a solid-state diffusion and dissolution-precipitation mode. The result show that the process of synthesis Al/Mg₂Si composite can be expressed as(1) solid combustion in the preheat phase, the combustion reaction between Mg,Al,Si particles started with the solid-state diffusion firstly; (2) liqid combustion in the combustion process, the solid-state diffusion reaction between Mg and Si particles led to the partial melt of Mg ,Al particles on the Mg,Si boundary; (3) cooling and crystal of the product after the reaction, the Mg₂Si grains precipitated from eutectic at the process .