Abstract
A semi-solid microstructure of Mg–10Zn–6.8Gd–4Y alloys is acquired via an isothermal heat treatment process, and the effects of the holding time on the microstructure evolution of Mg–10Zn–6.8Gd–4Y alloys are investigated. The results show that the microstructure of the cast alloy is composed of primary α-Mg dendritic grains with a eutectic structure (W-phase and eutectic Mg) distributed at the grain boundaries. The primary α-Mg dendritic grains grow in size with increasing holding time, and they tend to grow into more globular structures in the initial stage; they then become a bit more dendritic, as small branches grow from the grain boundaries after holding the sample at 580 °C for 10 min. Meanwhile, the interdiffusion of magnesium atoms within the eutectic region, and between the primary α-Mg and eutectic structure, leads to the formation of fine and relatively globular eutectic Mg grains in the eutectic structure after holding for 10 min. The eutectic Mg grains begin to grow, coarsen, coalesce, or be swallowed by the surrounding primary grains, causing fluctuations of the general grain size. Over the whole isothermal heat treatment process, two mechanisms—coalescence and Ostwald ripening—dominate the grain coarsening.
Highlights
Magnesium alloys have become important structural material candidates for applications in the automotive and aerospace industries alongside other fields due to their high specific strength and stiffness, as well as the simplicity of processing them to fabricate products [1]
Owing to the unique properties of rare-earth (RE) elements, their addition can significantly improve the performance of magnesium alloys [5]
Casting defects limit the addition of RE elements into magnesium alloys and restrict the application and development of rare-earth elements in magnesium alloys [8]
Summary
Magnesium alloys have become important structural material candidates for applications in the automotive and aerospace industries alongside other fields due to their high specific strength and stiffness, as well as the simplicity of processing them to fabricate products [1]. Elements has been proven to be a feasible and effective method to strengthen magnesium alloys [2,3,4]. Owing to the unique properties of rare-earth (RE) elements, their addition can significantly improve the performance of magnesium alloys [5]. The solid solubility of gadolinium (Gd) in magnesium can reach 24 wt.%, and this will lead to solid solution strengthening [4,6]. Yttrium has similar characteristics to Gd. Yttrium has similar characteristics to Gd It allows strengthening of magnesium by precipitation strengthening and solid solution strengthening [2]. Casting defects limit the addition of RE elements into magnesium alloys and restrict the application and development of rare-earth elements in magnesium alloys [8]
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