Effect of La,Zr micro-alloying on the microstructure and mechanical properties of Al-5Mg-0.2Ti alloy

Al-Mg-Ti alloys containing La and Zr elements were prepared by cast metallurgy. Effects of La and Zr additions on microstructure and mechanical properties of Al-Mg-Ti alloy were investigated by mechanical property test, optical microscopy, scanning electron microscopy, energy spectrum and X-ray diffraction. The results show that the addition of 0.2%Zr can positively refine the grain size, which indicates the composite refining effect of Ti and Zr is compatible, and the brittle phases of Al₃Zr precipitated in matrix can significantly increase the hardness of the alloys, but weaken the effect of grain refinement on the strength and ductility of the alloy. The combined addition of 0.2%La and 0.2%Zr possesses the excellent grain refining effect, when the average grain size of the alloy drops to only about 55 μm and the addition of La effectively avoids the precipitation and coarsening of brittle phase of Al₃Zr, thus improving the strength and ductility with the hardness changing slightly.