The Research On Synthesis And Mechanism Of Combustion Synthesis Of Al/Mg₂Si Composites

Because of its unique advantages,the self-propagating high-temperature synthesis(SHS) has become novel technology of producing compounds and composite materials.However,the knowledge of the reaction process and mechanism during combustion is extremely limited because of unique Mg-Si system and the rapid reaction process and high synthesis temperature.So the research on the mechanism of self-profection combustion syhthesis composite materials of toughening Al/Mg₂Si has its important significance in both the study on the combustion method itself and practical application and theoretical resrarch of Al/Mg₂Si.In this paper,a relatively general research on the weak exothermic reaction system of Al-Mg-Si has been made from thermo dynamics and structure dynamics. According to the thermodynamics theories,reaction free energy in Al-Mg-Si system have been calculated.The standard generationed free energy variation curve on each reaction of may occurring has been drawn.Through to the calculation of the adiabatic temperature in the ideal state reaction,the relationships between the preheating temperature,addition quantity of Al and adiabatic temperature has been made cleer.The dynamic parameters of combustion synthesis reaction system has been obtained which bases on the nonisothermal thermal analysis.Using the aluminum powder and mg powder as the raw material,the composite materials Al/Mg₂Si are syhthesis successfully by self-propagating combustion mode. The effect of different technical parameters in preparation on the phase compose and morphology of product has been studied,these parameters include poressrue,Al additive,Mg granularity.So the best scheme of preparing composite materials Al/Mg₂Si was summarized.The experiment of Combustion Front Quenching was brought to study the synthesis mechanism in reaction.Through to the scanning electron microscopy(SEM) and X-ray diffraction(XRD) on the microstructure transition in all reaction regions, the micro formation pross of the composite materials Al/Mg₂Si self-propagating high-temperature synthesis was exposed and the reaction mechanism was studied.The proliferation of dissolution precipitation was proposed as the chang mechanisms of self-propagating high temperature synthesis of composite materials Al/Mg₂Si.(l)When the temperature is low,Al,Mg,Si are solid-state,and the small amount phase of Mg₂si was generated basing on the diffusion between Mg and Si.This is the so-called solid-solid proliferation regime.(2) With increasing temperature,Al,Mg particles start melting and formate(Al,Mg,Si) Mg₂Si eutectic.And this process is the proliferation solid dissolved mechanism.(3)When the Mg,Si atoms in the liquid phase reach saturation,Mg₂Si phase precipitates from the liquid phase and grew up outside.And this process is dissolution precipitation mechanism.