Mg-6Al-(Sr,Ca)合金的显微组织和蠕变性能

MICROSTRUCTURE AND CREEP PROPERTIES OF Mg-6Al-(Sr, Ca) ALLOYS

系统研究了Mg-6Al-2Sr和Mg-6Al-(1-2)Sr-1Ca合金在水冷模铸造和压铸态下的显微组织、力学及蠕变性能．Mg-6Al-2Sr合金的铸态组织由α-Mg和沿枝晶界分布呈片状的α-Mg+Al4Sr共晶相组成．在Mg-6Al-2Sr基础上加入少量的Ca,合金中的Al4Sr被Mg2Ca取代,且出现了Mg—Al—Sr三元中间相,合金的抗蠕变性能显著提高．对蠕变后试样进行的扫描电镜观察表明, Mg-6Al合金中添加Sr和Ca后形成的中间相均具有很高的热稳定性．Mg-6Al-2Sr合金蠕变后的试样中出现了β-Mg17Al12相的非连续析出;而采用Sr和Ca复合合金化的试样显微组织在蠕变后无明显变化,也未析出β相,因而显著地提高了合金的抗蜗变性能．与水冷模铸造试样相比,压铸试样具有更细的显微组织和更高的室温与高温力学性能,但抗蠕变性能略低．

The microstructure, tensile and creep properties of Mg-6Al-2Sr and two Mg-6Al-（1- 2）Sr-lCa alloys have been investigated. The as-cast microstructure of Mg-6Al-2Sr alloy consists of the dendritic α-Mg and lamellar α-Mg＋Al4Sr eutectic at interdendrites. Ca addition to Mg-6Al-2Sr alloy results in the formations of Mg2Ca compound and a Mg-Al-Sr ternary intermediate phase, and the significant improvement of creep properties. SEM observations for crept samples revealed that the intermetallics in the Mg-6Al alloys with Sr and Ca additions have high thermodynamic stability. Discontinuous precipitation of β-Mg1τAl12 occurred in Mg-6Al-2Sr alloy during creeping, however, no obvious changes have been observed in the microstructure of the alloys with combined addition of Sr and Ca after creeping. The die-cast sample showed finer microstructure and higher tensile properties at room and elevated temperatures, but relatively lower creep resistance in comparison with the samples cast by water cooled mould.