Effect of long term annealing on the microstructure and tensile properties of hpdc AZ91 Mg alloy

This work is aimed to obtain the effect of long term annealing (LTA) on the tensile properties and on the microstructure of a high pressure die cast (hpdc) AZ91 Mg alloy. Tensile tests were performed on as-cast and LTA for 1000 h at 150 and 200 degrees C hpdc castings and the effect of LTA on the tensile properties such as yield strength (YS), ultimate tensile strength (UTS), ductility and fracture strain (FS) are confirmed. Additionally, explanations on micro failure mode of the material are presented to explain the influence of different micro features on failure of the material. The average size, area fraction and clustering tendency of beta(m) (massive) and beta(c+d) (continuous+discontinuous) Mg(17)Al(12) Particles are quantified and their effects on LTA are obtained. The results confirm that the UTS, YS, ductility and FS are mainly influenced by the area fraction, size distribution and spatial arrangement of beta particles. (C) 2007 Elsevier B.V. All rights reserved.