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Abstract. The modification effects of Al-RE (rare earth) and Al-5Ti-1B master alloys on the microstructure and mechanical properties of as-cast 5182 aluminum alloys were studied. Experimental results show that both of the modifications refine the Į-Al grains and the Mg 2 Si and (FeMn)Al 6 eutectics. The Mg 2 Al 3 phases exist in the forms of thin flake (ȕƍ-Mg 2 Al 3 ) and small granule (ȕ-Mg 2 Al 3 ) for the unmodified 5182 aluminum alloy. Modifications with 0.1 wt% Al-5Ti-1B and 0.2 wt% Al-RE yield longer flakes of ȕƍ-Mg 2 Al 3 and small amounts of ȕ-Mg 2 Al 3 granules. The other contents of the modifiers reduce the longer flakes of ȕƍ-Mg 2 Al 3 but facilitate formation of the particles and islands of ȕ-Mg 2 Al 3 . The 0.2 wt% of Al-RE modification yields the finest microstructure and the largest ductility; the 0.2 wt% of Al-5Ti-1B modification has better microstructure and the highest tensile strength.

ABSTRACT The microstructure and mechanical properties of continuously-cast 5182 aluminum alloy ingots with large-sections are not uniform，which depends on the diameter of ingots and the position where the sample locates. For the Φ160 ingot, the outer layer and middle layer have fine and uniform α-Al grains, while the centre appears the coarse α-Al dendrite. In contrary, the middle and centre layers appear the coarse α-Al dendrite, only the outer layer has the fine α-Al grains for the Φ380 ingot. The (FeMn)Al 6 and Mg 2 Si phases coexist in the primary α-Al grain boundaries and the Mg 2 Al 3 phases precipitate in the α-Al grains. By homogenously annealing, the Mg 2 Si and (FeMn)Al 6 phases are broken-up into dispersive islands and particles and the Mg 2 Al 3 phases precipitate more sufficiently in the forms of fine particles and short flakes. The elongation is largely enhanced; while the yield strength, tensile strength and hardness receive much less influence by the heat treatment. However, the homogenous annealing at 495 o C for 24 h is not enough for adjusting the microstructure of the Φ380 ingot.