Influence of alloying elements on precipitation formation and mechanical properties of Al-Cr-Mo-Sc-Zr alloys during laser powder bed fusion at room and elevated temperatures

Most of the high-strength aluminium alloys for Laser Powder Bed Fusion (L-PBF) in research are based on conventional hardenable Al-Cu, Al-Mg-Si and Al-Zn-Mg alloys that have issues with hot-cracking during the L-PBF process. This study investigates the effect of alloying elements on two novel Al-Cr-Mo-Sc-Zr alloys (Scancromal (R) variants) with a good, crack-free processability and strength-ductility combination. A layer thickness of 100 mu m was used, highlighting the high productivity and good processability of Al-Cr alloys. Heat treatments and hardness measurements were conducted to investigate peak age heat treatment and revealed a relation between Sc/Zr-ratio and peak aged temperature. SEM observations of small precipitates at grain boundaries and fracture surfaces contributed to understanding the changing fracture mechanism from less ductile (2.4-10.2% elongation) to very ductile (14.1-19% elongation). Tensile tests at elevated temperatures and creep tests showed a positive effect of Cr and Mo on high temperature strength. High-temperature properties, especially creep results of Al-Cr alloys and Scalmalloy (R) (Al-Mg-Mn-Sc-Zr) are presented for the first time and emphasize the increased heat-resistance by Cr and Mo. The threshold stress, below which theoretically no creep should occur, of the presented Scancromal (R) variants is at least 5 times higher (142-189 MPa) compared to Scalmalloy (R) (28 MPa). A comprehensive comparison of the results to literature values of AlSi10Mg, other Al-Cr alloys and high temperature Al alloys gives valuable insight on how the aging response, microstructure, ductility and high-temperature strength of this type of alloy is influenced by its alloying elements.