Comparative study of mechanical properties of cast and forged Al-3Mg-MnO(2) and Al-8Mg-MnO(2) composites

The Al-Mg-MnO(2) composite is a MnO(2) particulate reinforced Al metal matrix composite. Its substantial ductility makes it promising composite for study. The Al-3Mg-MnO(2) and Al-8Mg-MnO(2) composites were synthesized by stirring 3, 5, and 8 wt% of MnO(2) particulates in Al-3Mg melt and Al-8Mg melt to study their mechanical properties. Their microstructure shows intermetallic precipitates of Al, Mg, and Mn at dendrites, grain boundaries and within the grains. In both sets of composites, the hardness, and the yield strength increases with increasing MnO(2) content in the cast and forged composites. Both the groups of composites show an increase in tensile strength with increasing particle content from 3 to 5 wt%, a further increase in particle content to 8 wt%, leads to an abrupt decrease in tensile strength in both the group of composites. The percentage elongations in forged composites are lower than those in cast composites, but this decrease is more prominent in Al-8Mg-MnO(2) composites in comparison to Al-3Mg-MnO(2) composites. The J(IC) value decreases as the percentage of MnO(2) particles increases in Al-3Mg-MnO(2) and Al-8Mg-MnO(2) composites. Forging increases J(IC) values in both the class of composites in comparison to their cast counterparts due to work hardening and healing of pores. Crack growth toughness also decreases as the MnO(2) particle content increases in Al-3Mg-MnO(2) and Al-8Mg-MnO(2) composites. Forged Al-3Mg-MnO(2) shows decreased T/E ratio in comparison to their cast counterparts except at 8wt%. However, forged Al-8Mg-MnO(2) shows improved T/E at 3wt% and a drop at 5wt% and 8wt% MnO(2). Variation of crack growth toughness between cast and forged Al-8Mg-MnO(2) is minimal in comparison to that between cast and forged Al-3Mg-MnO(2) composites.