The Effect of La on the Microstructure and Mechanical Properties of the (Al) + Al₄(Ca,La) Wrought Alloys

Abstract—This article is devoted to optimization of the chemical composition of the high-tech Al–3 wt % Ca–(0.5–2.0) wt % La–1.5 wt % Mn alloys. The perspective of a decrease in the content of lanthanum from 2 to 0.5 wt % in new alloys has been validated using advanced methods for analyzing the structure and phase composition (electron microscopy, X-ray phase analysis, thermodynamic calculation) and using the analysis of mechanical (tensile) properties formed in the course of deformation treatment. The evolution of the structure of the alloys was studied in the course of thermodeformation treatment. It has been shown that upon hot rolling at 400°С with no preliminary annealing of ingots it is possible to obtain high-quality deformed semiproducts (sheets) with no surface and edge defects (up to a 90% reduction). The deformation treatment provides the formation of a structure with inclusions of a (Al,Mn)₄(Ca,La) eutectic phase uniformly distributed in an aluminum matrix and found in a form of ring-shaped precipitates of submicron sizes (300 × 150 nm). In addition, the formation of a net of low-angle boundaries (subgrains) with a mean size of ~1 μm is observed; some inclusions of a eutectic phase are found along these boundaries. This combination of structural characteristics mainly determines the ability of reaching favorable mechanical properties of an alloy after hot rolling with 0.5 wt % La (the ultimate strength of 240–260 MPa, yield strength of 185–205 MPa, and relative elongation of 5.5–9.0%), which are comparable with the properties of the previously studied alloy with up to 2 wt % La.