Granules Of Mg <sub> 2 </ Sub> Si Enhances The Eutectic Al-20% Si-based Composites

Particle reinforced aluminum metal matrix composites have many excellent mechanical properties and physical properties such as high specific strength and specific stiffness,resistant wear,anti-fatigue,low thermal coefficient of expansion,etc.They will increasingly be used in many fields such as aeronautics,astronautics,automobile and electron and so on.In this paper,the Mg₂Si particle reinforced hypereutectic Al-20%Si alloy in-situ composites are manufactured by DMR(Direct Melt Reaction). The most casting technique parameter of Mg₂Si/Al-Si composites has been investigated.The different Mg₂Si content(10%,12%,15%,18%,20%) of Mg₂Si/Al-Si composites has been manufactured by adding different contents of magnesium.The complex modification of 20%Mg₂Si/Al-Si composites has been conducted by adding different contents of P and La.After complex modification,heat treatment was used to the 20%Mg₂Si/Al-Si composites.The hardness and wear resistance of Mg₂Si/Al-Si composites were investigated.The results of the research are as follows:(1) The grains of Mg₂Si and primary silicon in the composites become fine at the pouring temperature 750℃.With the increase of the cooling rates,the microstructure and the hardness and wear resistance of the composite are obviously improved.The optimal casting technique parameter was:the pouring temperature is 750℃,cooling in the water.(2) With the content of Mg₂Si increasing,the morphology of primary Mg₂Si in the Mg₂Si/Al-Si composites has changed from polygon block to characters like and finally become coarse dendrite.(3) The complex modification of P and La has changed the morphology and size of the primary Mg₂Si in 20%Mg₂Si/Al-Si composites.With adding 0.1%P and 0.54%La,the morphology of the primary Mg₂Si in the microstructure has changed from coarse dendrite to small spherical particles,and the size of primary Mg₂Si decreased to about 14μm.(4) The modification mechanism of P was obtained,namely AlP in the melt could be as the nucleus of primary Mg₂Si,which can accelerate the nucleation of primary Mg₂Si and refinement the primary Mg₂Si.The modification mechanism of La was that La could form some white needle phase or some rich area of La,which can absorb in the growth front of the primary Mg₂Si,change the interface energy of primary Mg₂Si and inhibit its anisotropic growth,reach the effect to change the morphology of primary Mg₂Si.(5) Complex modification has improved the hardness and wear resistance of the 20% Mg₂Si/Al-Si composites . The composites with 0.1%P and 0.54%La have the optimal properties.Comparable with the non-modification composites,the hardness and the wear resistance are increased 26.25% and 55.6%,respectively. (6) The optimal heat treatment parameter in this study is:solute at 500℃for 10h and quench in room temperature water,aging at 175℃for 10h.After being treated by optimal heat treatment,the hardness and wear resistance of the composites have been improved,and increased 21.76% and 60.3%,respectively.In a word,the present study improved the structure of microstructure on Mg₂Si/Al-Si composites,enhanced the hardness and wear resistance of the material,which have instructing significance for the application of the Mg₂Si/Al-Si composites.