Effects of trace Mn addition on the elevated temperature tensile strength and microstructure of a low-iron Al–Si piston alloy

The effects of different amount of trace Mn addition on the elevated temperature tensile strength and microstructure of a low-iron Al–Si piston alloy were investigated by tensile testing, EPMA, SEM and EDX. It has been found that with the increase of Mn addition, the elevated temperature tensile strength of the examined alloy exhibits an interesting change: from primary 67.07 MPa, increased to 75.62 MPa and then decreased to 69.67 MPa, 63.72 MPa; finally increased again to 71.92 MPa. Through microstructural analysis, it is found that there occurs an evolution of Mn-bearing intermetallic phases in alloy with the increase of the Mn addition into the alloy. When the amount is 0.15 wt.%, most of manganese exists in the dendritic Al9FeNi phase; further addition of Mn can lead to the formation of plate-like Mn-bearing phases, whose strengthening effect is poor.