Effect of Mn Addition on the Phase Composition and Strengthening Behavior of AlCuYbZr and AlCuGdZr Alloys

The effects of Mn addition on the microstructure and strengthening of AlCuYbZr and AlCuGdZr alloys were investigated. Novel Al 80-88 Cu 8-12 Yb 3-4 Mn and Al 78-86 Cu 10-15 Gd 3-5 Mn phases solidify in the alloys instead of the Al 8 Cu 4 Yb and Al 8 Cu 4 Gd phases. Alloying by Mn provided novel phase formation and redistribution of Cu between the Al solid solution and the intermetallic phases. Three types of precipitates were identified in the microstructure after heat treatment: Al 3 (Zr,Yb)/Al 3 (Zr,Gd), Al 20 Cu 2 Mn 3 , and θ′(Al 2 Cu). The high Cu content in the Al solid solution with a combination of the Al 20 Cu 2 Mn 3 phase precipitates led to a 60-MPa to 80-MPa increase in YS relative to that of the Mn-free alloys.