Imparting high-temperature grain stability to an Al-Mg alloy

Al alloys, despite their excellent strength-to-weight ratio, cannot be used at elevated temperatures because of microstructural instability owing to grain growth and precipitate coarsening, thus, leading to a drastic loss in their strength. In this work, we have attempted to address the issue of grain growth by introducing in-situ formed polymer derived ceramics in an Al-Mg alloy. A stable grain structure with minimal loss in hardness when exposed to 450 °C and 550 °C for 1 hour was obtained due to the particle pinning of the grain boundaries by the Zener mechanism.This work was supported by the French State through the program “Investment in the future” operated by the National Re- search Agency (ANR) and referenced by ANR-11-LABX-0 0 08-01 (LabEx DAMAS). Abhishek Pariyar acknowledges the Ph.D. scholarship awarded by the Ministry of Human Resource Development, Govt. of India

Influence of laser beam welding parameters on the microstructure and mechanical behavior of Inconel X750 superalloy

In welding, the process parameters influence the mechanical properties of the joint. However, such investigations on laser welding of Inconel X750 are lacking despite its industrial significance. We performed such an investigation in which three parameter combinations, out of seven, exhibited full laser penetration (S1 (75 mm/min, 800 W), S2 (75 mm/min, 1200 W), and S3 (150 mm/min and 1200 W)). Microstructural analysis exhibited changes in the grain and dendrite morphology with columnar to equiaxed transition from the fusion boundary to the interior. S3 exhibited superior mechanical properties than others due to the smaller grain size and fusion zone.</p

Understanding process parameter-induced variability for tailoring precipitation behavior, grain structure, and mechanical properties of Al-Mg-Si-Mn alloy during solid-state additive manufacturing

Additive friction stir deposition (AFSD), a solid-state additive manufacturing technique, has excellent industrial application potential, particularly for Al alloys. However, in-depth process parameter-microstructure-property correlations are lacking, especially regarding precipitation behavior. In this work, AFSD of Al-Mg-Si-Mn alloy with various process parameter combinations was performed to understand the variation (by ∼ 70 %) in the nano/microhardness, concerning the precipitation behavior. The low nano/microhardness sample exhibited dissolution of the β” strengthening phase. However, higher nano/microhardness samples showed varying microstructural features with high dislocation density owing to fine-scale pre-β” precipitation and another sample possessed inhomogeneous β” phase distribution and β’ precipitation at the grain boundaries, thus exhibiting reprecipitation during AFSD. The variation in the grain structure was such that the high nano/microhardness samples exhibited large, elongated grains (∼11 to 13 µm) and low recrystallization fractions (∼16 –18 %) suggesting a predominantly non-recrystallized microstructure. Conversely, the lowest nano/microhardness sample exhibited the smallest grain size (∼5 µm) and, a higher recrystallization fraction (∼42 %). These findings demonstrate extensive variation in the precipitation behavior, grain structure, and mechanical properties due to the process parameters. Future applications can leverage this knowledge to tailor the microstructure and mechanical properties based on the identified process parameter combinations.</p

Friction stir processing of squeeze cast A356 with surface compacted graphene nanoplatelets (GNPs) for the synthesis of metal matrix composites

Friction stir processing (FSP) was applied to graphene nanoplatelets (GNPs) physically compacted on the surface of squeeze cast A356 alloy to incorporate GNPs within the matrix and to improve its mechanical properties. Squeeze casting resulted in finer size silicon and intermetallic compounds in cast microstructure, and subsequently FSP further refined the microstructure of squeeze cast A356 alloy, and GNP reinforced A356 alloy. The finer Si particles, intermetallics and graphene dispersed in the matrix increased the yield and ultimate tensile strength of FSP squeeze cast A356 alloy compared to the results reported in prior literature for FSP A356 alloy. Eutectic Si needles have been converted to fine spherical particles during FSP and were uniformly distributed within the nugget zone. The crystallite size of GNPs which were physically adhered to the surface of squeeze cast alloy prior to FSP decreased after FSP as a result of deformation. Thus, a combination of squeeze casting, and friction stir processing and incorporation of GNPs reinforcement in the A356 matrix is a promising route to further improve its mechanical properties