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

Abstract

Al1.5 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 "Mk of sorbital energy level as those of Al1.5Mn0.8 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 (• 0.2 ) of 67 MPa and ultimate tensile strength (• UTS ) of 160 MPa, although there was reduced in fracture strain (¾ 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 "Mk of the alloys. There was a good linear relationship between the nanoindentation hardness or rate of elastic deformation work in the ¡-Al phase and • 0.2 of the alloys. The dislocation density of Al1.5MnxSi alloys increased linearly as the "Mk-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 ¡ in Al1.5MnSi/Mg alloys. As the Mk ¡ changed, the • 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, • 0.2 , work hardening amount and dislocation density was predominantly consistent with that in the Mk ¡ or "Mk ¡ showing the indication of solid solution hardening level of the ¡-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.