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Coarse grain and poor thermal stability of Mg17Al12 are usually present in the as-cast Mg–Al alloys, which are detrimental to the mechanical properties. In this work, the microstructure evolution, and mechanical properties of as-cast AZ31-1Y alloy with different cooling rates (4.0–29.9 °C/s) were systematically investigated by thermal analysis and microstructure characterization. The results show that the addition of Y to AZ31 alloy results in the formation of primary Al2Y and eutectic Al2Y, while suppressing the formation of β-Mg17Al12. The AZ31-1Y alloy with a cooling rate of 29.9 °C/s exhibits the finest grain, with a grain refinement efficiency 40.9 % higher than that of AZ31 alloy with a cooling rate of 4.0 °C/s. After heat treatment, the acicular eutectic Al2Y is modified into a granular shape and numerous nano-sized Al2Y precipitates are observed within the α-Mg matrix. The addition of Y can effectively improve the mechanical properties of AZ31 alloy under high cooling rates, but the mechanical properties deteriorate at slower cooling rates due to stress concentration caused by the agglomeration of large-sized Al2Y particles. The optimal mechanical properties of the AZ31-1Y alloy are achieved at a cooling rate of 29.9 °C/s combined with subsequent heat treatment, and its YS, UTS, and EL reached up to 69 MPa, 293 MPa, and 14.5 %, respectively. Moreover, the related strengthening mechanisms are quantified. It is believed that this work can provide guidance for controlling the microstructure and optimizing the mechanical properties of as-cast Mg–Al alloys.

Martensitic stainless steels are widely used in industries due to their high strength and good corrosion resistance performance. Precipitation-hardened (PH) martensitic stainless steels feature very high strength compared with other stainless steels, around 3-4 times the strength of austenitic stainless steels such as 304 and 316. However, the poor workability due to the high strength and hardness induced by precipitation hardening limits the extensive utilization of PH stainless steels as structural components of complex shapes. Laser powder bed fusion (L-PBF) is an attractive additive manufacturing technology, which not only exhibits the advantages of producing complex and precise parts with a short lead time, but also avoids or reduces the subsequent machining process. In this review, the microstructures of martensitic stainless steels in the as-built state, as well as the effects of process parameters, building atmosphere, and heat treatments on the microstructures, are reviewed. Then, the characteristics of defects in the as-built state and the causes are specifically analyzed. Afterward, the effect of process parameters and heat treatment conditions on mechanical properties are summarized and reviewed. Finally, the remaining issues and suggestions on future research on L-PBF of martensitic precipitation-hardened stainless steels are put forward.