Effect of Si Addition on Microstructure and Mechanical Properties of Al–1.5%Mn Alloys

Abstract

Al–1.5 mass%Mn was chosen as the base alloy, and 1.0 and 3.3Si were added to the base alloys, keeping the same values in the ΔMk of s-orbital energy level as those of Al–1.5Mn–0.8 and 2.4Mg alloys with superior tensile properties for as-cast applications. The Si addition or increment in the base alloy showed strengthened tensile behavior of the 0.2% proof stress (σ_0.2) of 67 MPa and ultimate tensile strength (σ_UTS) of 160 MPa, although there was reduced in fracture strain (ε_f) to 9%. The increase and decrease in flow stress and strain, respectively, resulted from the increment in degree of solid solution strengthening by the increase of ΔMk of the alloys. There was a good linear relationship between the nanoindentation hardness or rate of elastic deformation work in the α-Al phase and σ_0.2 of the alloys. The dislocation density of Al–1.5Mn–xSi alloys increased linearly as the ΔMk-magnitude increased, compared with that of the base alloy. The behavior in the flow stress variation qualitatively agreed with that of dislocation density. There was a linear relationship between the lattice constant and Mk_α in Al–1.5Mn–Si/Mg alloys. As the Mk_α changed, the σ_0.2 of the alloys also increased and its increment rate was similar in both Si and Mg addition alloys. It may be considered that the trend of change in the lattice constant, σ_0.2, work hardening amount and dislocation density was predominantly consistent with that in the Mk_α or ΔMk_α showing the indication of solid solution hardening level of the α-Al phase, and the effect of difference of third elements such as Si and Mg on their mechanical properties could be ignored in tensile examination procedures in this study.