Preparation and compression property of Mg-5Al-xGd solid solution alloys

The solidification microstructure of the Mg-5Al alloy is controlled by the Gd content (0.00%, 0.25%, 0.50%, 0.75%, 1.00%, mass fraction, the same below) and high pressure (3 GPa), and the correlation between microstructure and compressive properties at room temperature was studied. The results show that the microstructure is single solid solution only when the the content of Gd is 0.75%, for the Mg-5Al-xGd alloys solidified under atmospheric pressure graphit mold casting. In the Mg-5Al-0.75Gd alloy, no eutectic phase form at the grain boundaries, granular Al2Gd phase is dispersed on the matrix, and the average grain size is about 85 μm. Moreover, the compressive strength and the maximum compressive strain of the Mg-5Al-0.75Gd alloy solidified under atmospheric pressure are 379 MPa and 33.46% respectively, which are higher than those of alloys with intergranular second phase. For the Mg-5Al-xGd alloys solidified under 3 GPa pressure, the microstructure is single solid solution when the Gd content is ≤ 0.25%, and there are eutectic phase Al2Gd at the grain boundaries (among dendrites) when the Gd content is ≥ 0.50%. In addition, the grain sizes of the Mg-5Al-0.25Gd and Mg-5Al-0.75 Gd alloys solidified under 3 GPa pressure are 74 μm and 38 μm respectively. However, the compressive strength and the maximum compressive strain of the Mg-5Al-0.25Gd alloy are 402 MPa and 33.61% respectively, which are superior than that of the Mg-5Al-0.75Gd alloy with the compressive strength of 341 MPa and the maximum compressive strain of 25.12%. Therefore, the existence form of Al and Gd at grain boundaries is an important factor affecting the mechanical properties of the Mg-5Al-xGd alloys.