Morphology evolution of Al9(Mn, Ni)2 eutectic phase in Al-4Ni-2Mn alloy during heat treatment at 350 °C

Abstract

The morphology evolution of Al9(Mn,Ni)2 eutectic phase in Al-4Ni-2Mn alloy at 350 °C was examined. Two kinds of morphology evolution trends of Al9(Mn,Ni)2 eutectic phase were observed by using scanning electron microscopy and transmission electron microscopy. The ribbon-like Al9(Mn,Ni)2 eutectic phase taking up a small portion of the eutectic structures gradually changes from ribbon-like morphology to rod-like during the heat treatment. The rod-like Al9(Mn,Ni)2 eutectics, primary eutectic structure in the alloy, become unstable at the transverse sub-boundaries of the eutectic rod when the samples are heat treated at 350 °C, and then split up into short rods with the extension of heat treatment time. Also, the Vickers microhardness test was used to characterize the change of local mechanical properties. The hardness test results indicate that local morphology evolution of eutectic phase has no obvious effect on the local mechanical properties of the alloy. The microhardness of the eutectic area increases slightly when the heat treatment time is extended to 192 h or 360 h.