Influences of Growth Velocity and Fe Content on Microstructure, Microhardness and Tensile Properties of Directionally Solidified Al-1.9Mn-xFe Ternary Alloys

In this study, influences of growth velocity and composition (Fe content) on the microstructure (rod spacing) and mechanical properties (microhardness, ultimate tensile strength and fracture surface) of Al-Mn-Fe ternary alloys have been investigated. Al-1.9 Mn-xFe (x= 0.5, 1.5 and 5 wt. %) were prepared using metals of 99.99% high purity in the vacuum atmosphere. At a constant temperature gradient (6.7 K/mm), these alloys were directionally solidified upwards under various growth velocities (8.3-978 mu m/s) using a Bridgman-type directional solidification furnace. The results show that two kinds of Al-rich alpha-Al phase and Fe-rich intermetallic (Al 6 FeMn) phase may be present in the final microstructures of the alloys when the Fe content increases from 0.5 wt.% to 5 wt.%. Al 6 FeMn intermetallic rod spacing, microhardness and ultimate tensile strength were measured and expressed as functions of growth velocity and Fe content by using a linear regression analysis method. According to experimental results, the microhardness and ultimate tensile strength of the solidified samples increase with increase in the growth velocity and Fe content and decrease in rod spacing. The elongations of the alloys decrease gradually with increasing growth velocity and Fe content.