Production and characterization of in-situ Al-Mn-Al2O3 composite produced in Al-MnO2 system

In this research, the fabrication of in situ Al-Mn-Al2O3 composite samples from different composition of Al-MnO2 as starting materials have been made by stir casting method. For this purpose, a mixture of Al and MnO2 powders with weight ratio 1:7 was ball-milled. Then 1, 3, 4 and 7wt% of this mixture along with 5%wt Mg (to improve wettability) have been added to melted aluminum at 900 ° C . The disperstion of added materials in molten of Al was made by using graphite stirrer during 8 minutes. The molten of composite was casted into a preheated steel mold. Differential thermal analysis (DTA) was conducted on starting powder mixtures to study the aluminothermic reaction and the possible other reaction or phase changes. XRD analysis and scanning electron microscopy (SEM) were used to investigate the microstructure and phase composition of composite samples. The results show that the final phase composition for all composites is solid solution of Al-Mn, ceramic phase of alumina and MnAl6 intermetallic compound. The amount of MnAl6 and Al2O3 particles in composite samples were increased by adding higher quantity of MnO2 into molten of Al. Moreover there is an optimal amount of MnO2 in which haighest mechanical properties such as hardness, strength and toughness is obtained for composite samples.