等温法半固态压铸组织和性能
(西北工业大学 材料科学与工程学院，西安 710071)
摘 要: 研究了Mg-5Al-1.5Ca-0.4Zn-0.2Mn-Sr-Ti合金的等温法半固态压铸组织和性能。 结果表明： 合金相组成为α(Mg)、 (α(Mg)+Al2Ca)共晶和少量球状Mg17Al12。 Sr变质合金在585 ℃等温法处理时， α(Mg)首先分离成核。 随着等温时间加长， α(Mg)由块状向球状转变。 25 min时， 转变为粒径40 μm的均匀球状组织。此后， 球晶发生长大， 进而聚拢合并。 合金等温法压铸实验发现, 组织为均匀细小等轴晶， 粒径25 μm。 合金室温和高温强度较砂铸大幅提高， 塑性略有下降。 这是由于细晶强化作用，以及晶粒细化使得晶界上半连续分布的Al2Ca相更弥散， 这样Al2Ca高温下钉扎晶界的作用更加突出。 等温法半固态压铸合金200 ℃的高温强度优于AZ91压铸合金， 可达140 MPa。
关键字: 半固态等温热处理；半固态压铸； 显微组织； 力学性能； 镁合金
pressure-casting process
（College of Materials Science and Engineering,
Northwestern Polytechnical University, Xi'an 710071, China）
Abstract: 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)+Al2Ca) eutectic and Mg17Al12. When the alloy modified by Sr is heattreated at 585 ℃, the primary α(Mg) phase divorces into lumps. Then the lumps evolve into spheroids gradually with isothermal time increasing. After treated for 25 min, the well-distributed spheroidic semisolid-structure with the average grain diameter of 40 μm 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 140 MPa, better apparently than that of AZ91 die-casting alloy. Homogeneous equiaxied fine grains with the average grain diameter of 25 μm are obtained in experimental alloy by the semi-solid isothermal heat-treatment-die-pressure casting process.
Key words: semi-solid isothermal heat-treatment(SSIT)； SSIT-die-pressure casting； microstructure； mechanical properties; magnesium alloy
