Effect of Mn Addition on the Mechanical Properties of Al–12.6Si Alloy: Role of Al15(MnFe)3Si2 Intermetallic and Microstructure Modification

Abstract: Effect of manganese (Mn) addition (0.0, 1.0, 2.0 and 3 wt%) on the microstructural morphology, hardness, tensile properties and fracture behaviour of the gravity cast eutectic Al–12.6Si alloy has been studied through XRD analysis, chemical analysis, optical metallography, FESEM analysis, energy dispersive spectroscopy analysis, hardness test, tensile test and quantitative phase analysis. As-cast Al–12.6Si–0.0Mn alloy has a non-uniformly distributed coarser and irregular shape primary and eutectic silicon particles inside the α-Al phase, and both the Si phase have very sharp corners. Whereas, the 1 wt% Mn added alloy has uniformly distributed fine eutectic and primary Si particles with blunt corners. Further, the addition of 1.0 wt% Mn forms very few (0.26 vol %) irregular shape Al<inf>15</inf>(MnFe)<inf>3</inf>Si<inf>2</inf> intermetallic phase within the α-Al phase and eutectic Si phase. But, 2.0 wt% and 3 wt% Mn added alloy has an irregular shape coarse plate-like Al<inf>15</inf>(MnFe)<inf>3</inf>Si<inf>2</inf> intermetallic phase besides the primary and eutectic Si phase. The bulk hardness of the Al–12.6Si alloy is increased with an increase in Mn concentration as the harder Al<inf>15</inf>(MnFe)<inf>3</inf>Si<inf>2</inf> intermetallic phase forms and both the Si phase morphology modify. The microhardness of the constituent phases also varies with the change in Mn concentration in the alloy. The Mn addition improved the ultimate tensile strength, yield strength, and elongation (%) of the alloy. However, fractographs reveal that the brittle mode of fracture has been increased due to the presence of a higher volume of brittle Al<inf>15</inf>(MnFe)<inf>3</inf>Si<inf>2</inf> intermetallic in 2.0 and 3.0% Mn alloy. On the other hand, the amount of brittle and cleavage fracture of Si particles decreased, and ductile fracture with dimples formation increased in 1.0 wt%Mn added alloy. Graphic Abstract: [Figure not available: see fulltext.]