Abstract
This study introduces a family of unique Al–Mn–Cr–Zr-based aluminium alloys illustrated by two ternary and one quaternary variants. The choice of alloy compositions has created a system resistant to solidification cracking while retaining high amount of solutes in solid solution in as-printed condition. Good relative density (~ 99.5%) has been demonstrated along with microstructural study supported by X-ray diffraction to display solidification structure with nanometric precipitate formation in small amounts in as-printed condition. High levels of Mn and Cr produce significant solid solution strengthening reaching hardness of up to 102 HV in as-printed condition. Additionally, the combination of Mn, Cr and Zr is shown to be important to control precipitation strengthening upon direct ageing and coarsening resistance due to slow diffusivity. To elucidate the concept of precipitation strengthening, one set of alloys was aged at 678 K between 0 and 10 h and microhardness results showed that average hardness response reached 130 HV for the quarternary alloy.Graphical abstract
Highlights
Aluminium (Al) is the most abundant metal on the earth’s crust and is the second most mined metal after iron [1]
It has been shown that transition elements such as Mn, Cr, Fe and Ni could be game changers if their solubility could be increased in Al alloys, since they add high misfit strains to Al-matrix
This means that depending on the cooling rate, the solubility seen at a higher temperature can be realised after solidification
Summary
Aluminium (Al) is the most abundant metal on the earth’s crust and is the second most mined metal after iron [1]. Aluminium is known for various secondary properties, such as high thermal and electrical conductivity making it suitable for applications requiring heat loss or electrical conductivity along with high specific strength. The PBF-LB process can create components by rapidly melting and solidifying the material which is in the form of a thin powder layer (usually 20-60 μm) to solid components. This is repeated by the re-melting and reheating of previously solidified layers, forming a complex microstructure. This complicated process, creates the need for new or modified material compositions. Some researchers have addressed the solidification cracking issue by modifying the solidification process of aluminium by creating alternate solidification paths for Al-grains by providing nucleants (such as Al3(Sc,Zr) or TiB2)
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