Tem Observation of Precipitates in Al-Mg-Ge Alloys with Different Mg2Ge Contents

It has been known that Al-Mg-Ge alloy shows the similar precipitation sequence to Al-Mg-Si alloy, and its equilibrium phase is β-Mg₂Ge according to its phase diagram. In this study, the precipitation sequence of Al-Mg-Ge alloys containing different contents of Mg₂Ge has been investigated by hardness test, TEM and HRTEM observation to understand the effect of Mg₂Ge contents on age-hardening behavior of these alloys. The hardness of as-quenched and peak-aged samples was improved by increasing Mg₂Ge contents. There was no big difference between peak hardness of the alloys with higher Mg₂Ge contents aged at 423, 473 and 523 K, which was different from the result of the alloys with lower Mg₂Ge contents. The precipitates in the peak-aged samples were classified as some metastable phases, i.e. the β’-phase and parallelogram-type precipitates by HRTEM observation. The relative frequency of these precipitates in the matrix changed with Mg₂Ge contents.