The divorce associate coarse β-Al12Mg17 distributed along the grain boundary will dissolved in the base to form supersaturated solid solution of α- Mg when AZ91HP die casting was heated to 415 ℃ for 8 hours and then quenched. The β - Al12Mg17 will
precipitated as
continuous and non-continuous form during artificial aging. Non - continuous β - Al12 Mg17 precipitates earlier and more than continuous β -Al12Mg17. The
morphology and amount of non- continuous β-Al12Mg17
changed with aging time and had a great effect on the
properties of the alloy. The microstructure observation shown that nucleation of non - continuous β - Al12 Mg17 precipitated as the granules along the grain boundaries first, and then it grew up and changed the morphology into the mixture of block and cell, finally the blocks of β - Al12 Mg17 disappeared and the cells extended into the crystal grains. Along with the course of precipitations its morphology changed and the mechanical properties of AZ91HP were also changed and shown obvious precipitation hardening.
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