Study On The Strengthening Mechanism Of N-SiCp/AZ91D Composites

Based on theoretical calculations, the strengthening mechanism ofnano-sized SiC particles (n-SiCp) reinforced AZ91D magnesium matrixcomposites (n-SiCp/AZ91D) was studied. An analytical modol for predictingthe composites’ yield strength was developed. The n-SiCp/AZ91D compositeswere fabricated by mechanical stirring and high intensity ultrasonic dispersionmethod. Microstructure of n-SiCp/AZ91D composites were analysed byscanning electron microscope (SEM) and optical microscope. The mechanicalpropreties were tested by electronic universal testing machine. And theprediction was in good agreement with the experimental data.The results showed that, the Orowan strengthening, the themal mismatchstrengthening and Hall-Petch strengthening are the main strengtheningmechanism of n-SiCp/AZ91D composites. And the distribution of the particlesin the matrix has an important influence on the enhancement effect. When theparticles completely distributed within the grain, the composites had the beststrengthening effect. Meanwhile the Orowan strengthening and the themalmismatch strengthening were the dominant strengthening mechanism. On thecontrary, the composites showed the least strengthening effect while theparticles distributed along the grain boundary. The main strengtheningmechanism was the Hall-Petch strengthening. When the particles wereintragranular-boundary distribution, the Orowan strengthening, the themalmismatch strengthening and Hall-Petch strengthening all effected. And thestrengthening effect decreased as the proportion between the particle inside thegrain and on the grain boundary decreased. Moreover the strengthening effectswere weakened because of the aggregation and segregation of the particles.The n-SiCp were almost uniformly dispersed in the n-SiCp/AZ91Dcomposites. There were no big aggregates but still small aggregates andsegregation which would decrease the enhancement effect of the particals.Minority n-SiCp was intragranular distribution while most of the n-SiCp weregrain boundary distribution and mainly dispersed around the β-Mg17Al12phase. The grains of the n-SiCp/AZ91D composites were getting finer with theincreasing content of n-SiCp which made the Hall-Petch strengthening effect.As the content of n-SiCp was increasing, the room-temperature mechanicalproperties of the n-SiCp/AZ91D composites were significantly improved. Thetensile strength, yield strength, percentage elongation, reduction of area of thecomposites were always enhancing first and then dropping. The mechanicalproperties reached the maximum when the content of the n-SiCp was1.5wt%,and then dropped with the content of2.0wt%. The experimental data showedgood agreement with the prediction.