Preparation And Characterization Of Al/Mg₂Si Composite Material

Intermetallic compound Mg₂Si is fit for moderate and high temperature structural material and hopeful to be used in aeronautics, astronautics and automotive industry.Because it has many virtues such as low density, high melting point and high specific strength etc.But it is very difficult to process because of its intrinsic embrittlement. So the research of improving the brittleness of Mg₂Si has a far importance at not only theoretical side but also practical application side.In this paper, Al/Mg2Si composite material which was based on intermetallic compound Mg₂Si and added with tenacious phase-Al was prepared by combustion synthesis and solid-state reaction actived by milling.In ideal state the relationships of preheat temperature vs adiabatic temperature and quantity of diluents vs adiabatic temperature were caculated.The results show that with the increasing of preheat temperature the adiabatic temperature of Mg-Si-Al system increases and reaches a flatform finally;with the increasing of quantity of diluents the adiabatic temperature decreases,so dose platform.Influential factors like preheating velocity, pressure of green compact, powder size of Mg, Al(vol)% and the hole in the bottom of the sample during the preparation of Al/Mg2Si composite by combustion synthesis method were disscused about phase and compactness of samples.The investigation indicats that the influences of single factor are different on samples' compactness.But there is a regulation can be gotten, which is:influence of powder size of Mg>influence of preheating velocity>influence of pressure of green compact.In the meantime, the influences of powder size of Mg milling time and process control agent (PCA) had been researched. It is found that the decrease of Mg powder size speeds up the reaction of Mg and Si. When the powder size of Mg ranges from 178μm to 250μm, the amount of Mg₂Si formed is small after milling for 50 hours. It is indicated that ball milling has a low efficiency in mechincal alloying between Mg and Si. In the milling process, with increased milling duration,the grain size of Si powder decreases and the micro-strain increases.Finally they all approach constants as limits. After 50 hours of MA, the MAed powder was annealed. It was found that Mg₂Si was formed at about 180°C .While the green powder, which was not milled, was annealed and the formatiom of Mg₂Si took place at around 530°C.It showed that the temperature of the solid-state reaction milled for 50h was lower 350°C than that of unmilled. So itilluminates that the ball milling can decrease the temperature of solid-state reaction greatly and take a part in mechanical activation. During the annealing process, the growth curve of the nano-Mg2Si grain has two obvious stages: the slow growth stage at low temperature (190°C