Affiliation: | Department of Materials Science and Engineering, National Tsing-Hua University, Hsinchu, Taiwan, ROC |
Abstract: | The Al2O3 particles are introduced into the Al-4wt.%Mg melt by the “vortex” method. After being cast, Al2O3-(Al-4wt.%Mg) composites are remelted at 700, 750, 800 and 850°C for different residence times to investigate the formation of MgAl2O4 (spinel). The results show that MgAl2O4 is the unique interface of the Al2O3-(Al---Mg) composites held at 700–850°C. Fine MgAl2O4 crystals grow on the surface of the Al2O3 particle but, as the holding temperature and the residence time increase, some spinels will form themselves into pyramidal shape. The MgAl2O4 grows not only at the matrix-particle interface but also on the surface of the composite specimens. The formation reactions of interfacial MgAl2O4 are as follows: Mg(1) + 2Al(1) + 2O2(g) = MgAl2O4(s)3Mg(1) + 4Al2O3(s) = 3MgAl2O4(s) + 2Al(1) Both of them are equally important. |