Structure and mechanical properties of rapidly solidified magnesium based Mg-AI-Zn-RE alloys consolidated by extrusion

Magnesium based Mg-9Al-1Zn-5RE ( RE = La or Nd) alloys were rapidly solidified by chill block melt spinning. The resulting ribbons were cold packed into an aluminium alloy can and extruded at temperatures of 230 and 340°C and ratios of 20:1 or 25:1. Tensile and hardness tests of the extruded and heat treated materials were carried out. The tensile strength and elongation to fracture of the as extruded material were 478 MN m^-2 and 6·5% respectively and those of the material heat treated for 2 h at 350°C were 420 MN m^-2 and 20% respectively. The microstructure of these specimens was studied by X-ray diffraction and transmission electron microscopy. Intermetallics of Al₁₁ La₃ or Al₂Nd were found at grain boundaries and in the matrix which had a grain size of between 0·26 and 0· μm, while Mg₁₇Al₁₂ precipitates were present in the specimens extruded at a lower temperature (230°C). Yield strengths were consistent with the Hall-Fetch relationship with grain size established earlier for this class of material.