High-tech alloys based on Al – Ca – La(–Mn) eutectic system for casting, metal forming and selective laser melting

Abstract

Electron microscopy structure studies have shown that new Al3Ca2La(1–2)Mn system alloys have a fine hypoeutectic structure. The fine eutectic fibers are a few microns in length and less than one micron in thickness. EMPA shows that calcium and lanthanum are completely included in the eutectic, while manganese is distributed between the aluminum solid solution (Al) and the eutectic. The solubility of manganese in (Al) is about 1.7 wt.%. Addition of 2 wt.% Mn leads to a substantial increase in the yield strength and ultimate tensile strength of the base Al3Ca2La alloy whereas the ductility is not less than 5%. The yield strength of the quaternary alloy is about 175 MPa which is three times that of the base alloy. Due to the narrow solidification range and a high fraction of eutectic, new Al – (3–6)Ca – (2–4)La – (1–2)Mn alloys also have a lower hot tearing tendency comparable to that of the branded hypoeutectic and hypereutectic Al – Si alloys. The ball-milled experimental powder has been used for a preliminary analysis of the effect of selective laser melting on the as-built microstructure of the model hypereutectic alloy. No cracks and porosity have been observed, the microstructure consisting of very fine eutectic. The microhardness of the asprocessed alloy is about 170 HV which is comparable with the hardness of high-strength aluminum alloys. Thus, based on the analysis above, new alloys can be considered as promising for conventional casting and SLM technique instead of the widely used Al – Si alloys. The Al3Ca2La1Mn alloy has also been deformed by radial shear rolling. Hot rolling at 400 oC at a total pulling rate of μ = 8.16 has yielded high-quality 14 mm diameter rods. Microstructure analysis has shown that deformation leads to additional refining of eutectic crystals the average size of which is at a submicron level (300–500 nm). The combination of size of fine eutectic particles and their high volume fraction (~15%) allows reaching good mechanical properties, i.e., an ultimate strength of at least 230 MPa at a relative elongation of at least 15%. Thus the achieved combination of the properties of the new Al – Ca – La(–Mn) alloys allows classing them as high-tech materials suitable for advanced hybrid forming technologies.The study was carried out with the financial support of the grant of the Russian Science Foundation (Project № 18-79-00345).