Microstructure and mechanical properties of AlTiCrFe and AlTiCrCu alloys processed by Laser Powder Bed Fusion

Abstract

Additive manufacturing (AM) of aluminium alloys urges new alloy compositions to meet the requirements for high-strength and processability of the engineering products. This research focuses on the development of two Al alloys, AlTiCrFe and AlTiCrCu, with the goal to exploit the potential of transition element additions for grain refinement and increasing strength. Robust processability and build rates are reached for the two alloys, with no cracks and high density up to 99.8%. AlTiCrFe shows a bimodal microstructure, with the presence of ultrafine and fine grained zones, that can be attributed to a dual precipitation stage. Al3Ti precipitates are present in the ultrafine grained zone, confirming the effectivity of Ti as grain refiner. In addition, Al6Fe precipitates are present in the fine grained region, as a consequence of the later precipitation stage. AlTiCrCu, on the contrary, shows an homogeneous ultrafine grain microstructure, with Cu segregating at the grain boundaries. SAED analyses confirm the phase identification with the presence of high volume density cubic precipitates of Al3Ti_L12. AlTiCrFe and AlTiCrCu exhibit a yield strength value of 363 ± 1 MPa and 340 ± 1 MPa, respectively. These findings indicate that the two alloys open up new possibilities for a novel class of aluminium alloys for AM, leveraging the incorporation of transition elements, which aids in achieving strength during the as-built state, eliminating the requirement for supplementary heat treatment.