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

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 struc-ture 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 distrib-uted 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 struc-tural 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 rel-ative elongation of 5.5–9.0%), which are comparable with the properties of the previously studied alloy with up to 2 wt % La.