The effect of low content additives on strength, resistivity and microstructural changes in wire drawing of 1xxx series aluminium alloys for electrical purposes

Abstract The influence of the wire drawing process on the microstructure, mechanical properties and electrical conductivity/resistivity of 99.9% aluminium and alloys of aluminium obtained by adding 0.2 wt% of Mg, Co and Ce to technically pure aluminium was investigated. The purpose of the study was to obtain a material after the drawing process with an ultimate tensile strength (UTS) above 170 MPa, a conductivity higher than 60.4% according to the International Annealed Copper Standard (IACS), and the highest possible thermal stability. The study showed that an increase in strain leads to an increase in material strength properties and a decrease in electrical conductivity, but different additives have different effects on these properties. After wire drawing, 99.9% aluminium exhibits UTS at a level of 200 MPa and 61.1% IACS conductivity. The UTS and the conductivity of alloys with the addition of 0.2 wt% of Mg, Co, Ce in similar conditions are 252 MPa/59.1%, 203 MPa/60.5% and 184 MPa/60.9%, respectively. Microstructure was analysed using scanning electron microscopy to determine changes which occur during the wire drawing process. The analysis also included orientation imaging microscopy by means of electron backscattered diffraction, used to evaluate grain size and local texture. A thermal stability study was also performed to investigate the behaviour of material exposed to elevated temperatures. A decrease in the UTS of 16.8% was found during the thermal stability test for Al99.9%, while additions of 0.2% Mg, Co and Ce resulted in decreases of 8.1%, 12.8% and 9.1%, respectively. An improvement in thermal stability for the alloy with magnesium was identified by the solute drag mechanism. For alloys with the addition of Co and Ce, better thermal stability resulted from the appearance of new phases: Al9.02Co1.51Fe0.47 and Al4Ce, respectively. Finally, the potential application of these materials for electric cables is analysed and discussed.