The
microstructure and properties of Mg-5Al-1.5Ca-0.4Zn-0.2Mn-Sr-Ti
magnesium alloy by semi-solid
isothermal heat-treatment-die-pressure-casting process were studied. It is found that there are three main phases formed in the
experimental alloy, i.e., α(Mg), (α(Mg)+Al_2Ca) eutectic and Mg_(17)Al_(12). When the
Alloy modified by Sr is heat-treated at 585℃, the primary α(Mg) phase divorces into lumps. Then the lumps evolve into spheroids gradually with isothermal time increasing. After treated for 25min, the well-distributed spheroidic semisolid-structure with the average grain diameter of 40μm is formed, then the spheroids agglomerate and coalesce. It is also found that the room temperature
mechanical properties are improved greatly by semi-solid isothermal heat-treatment-die-pressure
casting process. The elevated temperature strength of experimental alloy at 200℃ is up to 140MPa, better apparently than that of AZ91 die-casting alloy. Homogeneous equiaxied fine grains with the average grain diameter of 25μm are obtained in experimental alloy by the semi-solid isothermal heat-treatment-die-pressure casting process.
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