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The limited mechanical properties of Al–Si alloys hinder their application in demanding and extreme conditions. The cracking tendency of high-strength aluminum alloys and high-cost of rare-earth elements pose challenges for the large-scale application of aluminum alloys in additive manufacturing. The novel and practical high-speed scanning remelting proposed in this study enables Al–Si alloys to exhibit significant proportion of fine microstructures and nano-precipitates, surpassing the mechanical properties of aluminum alloys fabricated by normal methods with exceptional strength (496.1 ± 5.8 MPa) and plasticity (21.4 ± 0.9%). This in-situ microstructure control method opens new pathways for the application in demanding engineering contexts. [ABSTRACT FROM AUTHOR]

The microstructure and properties of nickel-based superalloys under thermal exposure are the key basis for evaluating the high-temperature stability and proposing process optimization strategies. This study investigated the microstructural evolution and the corresponding tensile properties of IN738 alloy with different post-processing states under thermal exposure at 700 °C. The results show that the microstructures of IN738 alloys with different post-processing states (i.e., hot isostatic pressing (HIP) and standard heat treatment (SHT)) are significantly different. For the HIPed sample, large cuboidal γ′ and a small number of ultra-fine spheroidal γ′ precipitates are present in the γ matrix. Under thermal exposure, the size and volume fraction of ultra-fine spheroidal γ′ increase with prolonged thermal exposure time. In comparison, the SHTed sample is characterized as a bimodal distribution of γ′, with large primary cuboidal γ′ and small secondary spherical γ′. The size and volume fraction of primary γ′ increase first and then remain steady under thermal exposure. In particular, the tensile properties under exposure depend highly on the post-processing states. The increase of tensile strength after the thermal exposure in the HIPed sample is attributed to the rising fine spherical γ′ volume fraction. The rising size and volume fraction of primary γ′ in the SHTed sample improve the tensile strength during thermal exposure. • Microstructure and mechanical properties of IN738 highly depend on post-processing states. • Increase of strength in HIPed sample is attributed to rising fine spherical γ′ fraction after thermal exposure. • Rising size and fraction of primary γ′ in SHTed sample improve strength during thermal exposure. [ABSTRACT FROM AUTHOR]

Laser powder bed fusion (L-PBF) is a promising technique for fabricating high-performance complex aluminum (Al) alloy components. However, conventional high-strength wrought Al alloys that are processed using L-PBF have limited application owing to their poor cracking resistance. To investigate the cracking mechanism, L-PBF was used to fabricate a 2024Al alloy. The resultant microstructure exhibited severe hot cracking, which occurred at grain boundaries with a high angle in both solidification and liquation cracks. Increasing the scanning speed increased the susceptibility to cracking. The effect of scanning speed on the eutectics content of Al 2 Cu and Al 2 CuMg and the residual stress in as-fabricated samples are discussed. Crack elimination at a low scanning speed could be ascribed to the lower thermal stresses and adequate liquid feeding during the late stage of solidification. In addition, based on the RDG (Rappaz-Drezet-Gremaud) model, a cracking susceptibility map was produced, in which the cracking susceptibility was determined to increase with an increase in the solidification rate, in agreement with experimental observation. • Cracking mechanism in L-PBFed high-strength 2024Al alloy is determined. • Crack elimination at low scan speed is attributed to the low thermal stress and sufficient liquid feeding. • The cracking susceptibility map is established based on RDG model. [ABSTRACT FROM AUTHOR]