Microstructure and mechanical properties of rapidly solidified Al-Mn-Cr-Si alloy foils

Four alloys of Al-3.8 mol%Mn-0.9 mol%Cr-Xmol%Si(X = 0, 1, 2, 4) were rapidly solidified to foils with 60-70 mu m thicknesses and 6 mm width by the planar flow casting method. The effects of silicon addition amount to an Al-3.8 mol%Mn-0.9 mol%Cr alloy have been investigated by examining the microstructures and mechanical properties of the as-solidified and subsequently annealed foils. As for the alloys of Al-3.8 mol%Mn-0.9 mol%Cr-Xmol%Si(X = 0, 1), the precipitation of Al-12(Cr, Mn) occurs on annealing, accompanying the decomposition of supersaturated solid solutions resulting in the increase in hardness. These alloys annealed at 800 K for 7.2 ks, which contain largely grown Al-12(Cr, Mn), have a poor ductility of 0.4% in fracture strain. In the alloys of Al-3.8 mol%Mn-0.9 mol%Cr-Xmol%Si(X = 2, 4), the precipitation of Al-12(Cr, Mn) does not occur on annealing and the gradual decrease in hardness takes place with the increase in annealing temperature. These alloys annealed at 800 K for 7.2 ks, which contain relatively fine particles of Al15Mn3Si2 and Al7Cr, have an improved ductility of more than 1.2% in fracture strain. It is found that regardless of annealing temperature, the alloy containing 2 mol% silicon has good ductilities as well as relatively high 0.2% proof stresses and tensile strengths.