Effect of calcium on electrical resistance and phase composition of Al – 1.5 % Mn alloy

Abstract

The authors used experimental and modelling techniques to look at the specific electrical resistance and phase composition of low-alloy Al – Ca – Mn alloys after they had been subjected to various annealing regimes. The study focused on four alloys in the form of ingots and cold-rolled sheets containing 1.5% Mn and up to 1% Ca. Templates cut out of ingots and sheets were annealed in a muffle furnace using multi-stage modes in the temperature range of 300 to 600 oC. They were soaked for 3 hours at each stage of the process and air cooled after each stage. It was found that, in the as-cast state, all manganese in all four alloys makes a part of the aluminium solution (Al), whereas calcium is comprised in the (Al) + Al4Ca eutectic, which agrees with the Sheil-Gulliver non-equilibrium solidification simulation. Annealing of cold-rolled sheets for 3 hours at 600 oC results in an equilibrium phase composition and a uniform structure – i. e. globular submicron particles evenly distributed throughout the aluminium matrix. In their initial state, when almost all Mn is comprised in (Al), the ingots and coldrolled sheets of all the studied alloys have little to no difference between each other in terms of specific electrical resistance. On the other hand, Ca helps to significantly lower the specific resistance (by 6 μΩ·mm) compared with the base alloy after cold-rolled sheets have been annealed at 350–400 oC. It may be attributed to a higher rate of aluminium solution breakdown, which is associated with a dropping concentration of Mn in (Al) and Al10CaMn2 particles forming in line with the Al – Ca – Mn phase diagram.This research was funded under Grant of the Russian Science Foundation N 20-19-00746.