Structure and heat resistance of high strength Al–3.3%Cu–2.5%Mn–0.5%Zr (wt%) conductive wire alloy manufactured by electromagnetic casting

Abstract

The Al-3.3Cu-2.5Mn-0.5Zr (wt%) alloy was manufactured by electromagnetic casting and further subjected to processing including cold rolling, drawing and annealing. Excellent processability of the alloy at cold rolling and drawing was observed due to the ultrafine as-cast structure. Annealing of the cold-rolled strip at 350 °C for 48 h insignificantly reduces the hardness, but the electrical resistivity (ER) decreases by almost 3 times (from 115 to 40 nΩm). The large deformation during rolling (reduction 98.4%) and high fraction of the Zr- and Mn-bearing nano dispersoids (Al20Cu2Mn3 and Al3Zr-L12) stipulated the high set of mechanical properties and electrical conductivity after annealing at 400 °C (UTS~330 MPa, YS~250 MPa, EL~7%, 42.5 IACS). A model of ER dependence on the phase composition was proposed. While at above 400 °C there is a good agreement between the calculated and experimental values, the scatter at lower temperatures is attributed to exposure times insufficient for achieving the equilibrium (Al) composition. Atom probe tomography was employed for observation of Cu, Mn and Zr concentrations in (Al) after annealing at 350–450 °C. According to the experimental results and root-mean-square calculations, annealing at between 350 and 400 °C allows achieving (Al) compositions close to the equilibrium in reasonable time while with decreasing temperature the diffusion of Zr in (Al) decreases and thus it requires extremely long exposures, e.g. at 300 °C it is about 23,000 h. From this viewpoint annealing at below 350 °C is unreasonable for achieving lower ER.