Effect of Zr Microalloying on the Microstructures and Strengthening Mechanism of As-Cast Al-Fe-Zr Alloys

The microstructure and mechanical properties of Al-0.35Fe alloys with a series of different zirconium (Zr) additions from 0.1 to 0.4% are investigated by optical microscopy, scanning electron microscopy, transmission electron microscopy and tensile testing. The as-cast structure of the alloys varies with the Zr content. When the content of Zr is 0.1%, Zr dissolves into the aluminum (Al) matrix completely and iron (Fe) concentrates along the boundary in a network of eutectic Al(3)Fe. With the increase in Zr content to 0.2% and above, nanoscale Al(3)Zr particles appear in the alloy. With the Zr content increasing from 0.1 to 0.4%, the grain size of the Al matrix decreases from 73 to 23 μm. The morphology of the eutectic Al(3)Fe phase changes from short rod-like to an agglomerated structure consisting of finer and shorter rod-like shapes. The tensile and yield strengths increase while the total elongation decreases with increasing Zr content. The strengthening mechanism of the alloy can be attributed to the combination of fine-grain, solution and second-phase strengthening.