Advanced thermal-resistant aluminum conductor alloys: A comprehensive review

Abstract

This review provides a comprehensive overview of recent advancements in aluminum-based conductor alloys engineered to achieve superior mechanical strength and thermal stability without sacrificing electrical conductivity. Particular emphasis is placed on the role of microalloying elements—particularly Sc and Zr—in promoting the formation of coherent nanoscale precipitates such as Al3Zr, Al3Sc, and core–shell Al3(Sc,Zr) with metastable L12 crystal structures. These precipitates contribute significantly to high-temperature performance by enabling precipitation strengthening and stabilizing grain boundaries. The review also explores the emerging role of other rare earth elements (REEs), such as erbium (Er), in accelerating precipitation kinetics and improving thermal stability by retarding coarsening. Additionally, recent advancements in thermomechanical processing strategies are examined, with a focus on scalable approaches to optimize the strength–conductivity balance. These approaches involve multi-step heat treatments and carefully controlled manufacturing sequences, particularly the combination of cold drawing and aging treatment to promote uniform and effective precipitation. This review offers valuable insights to guide the development of cost-effective, high-strength, heat-resistant aluminum alloys beyond conductor applications, particularly those strengthened through microalloying with Sc and Zr.

1. Introduction

With the advancement of technology and expanding economic activities, energy consumption is increasing significantly, leading to a rapid growth in the demand for efficient power transmission and distribution systems [1–2]. As a result, there has been significant research in recent decades focused on developing conductors that combine superior strength with high electrical conductivity (EC). Copper conductors are widely valued for their exceptional EC and durability, making them the benchmark in power transmission and electronics. However, aluminium (Al) is increasingly replacing copper (Cu) due to its lower cost, lighter weight, higher strength/weight ratio and relative abundance, offering a more economical and sustainable alternative in various applications [3–4].

Common types of Al alloy electric conductors include all-Al alloy conductors (AAAC), Al conductor steel reinforced (ACSR), and electrical bus bars which are made by hot deformation, e.g., rolling or extrusion [4–6]. The AAAC type is composed entirely of Al alloy strands twisted together to form a single conductor cable. These conductors are specifically chosen for their mechanical strength, EC, and resistance to environmental factors. The 6xxx Al–Mg–Si alloys are generally used to make AAAC, specifically alloys AA6201 and AA6101 [7–10]. The ACSR conductors consist of Al strands surrounding a central steel core. The steel core provides mechanical strength, while the aluminum strands offer good conductivity. Alloy AA1350 is commonly used in such conductors [11]. Additionally, Al electrical bus bars are commonly manufactured in a rectangular bar form using alloys like AA6101 or AA1350, to efficiently distribute electrical power [12–13].

With rising energy consumption, the demand for conducting wires capable of carrying high currents has increased, inevitably raising the wire temperatures. Elevated temperatures severely degrade the mechanical properties of Al wires, compromising power network reliability. Conventional 6xxx series Al alloys, limited by poor thermal resistance, struggle to meet these requirements due to the coarsening or dissolution of strengthening precipitates, restricting their prolonged service temperature to 100°C and limiting current-carrying capacity [14–16]. Recent work has aimed at developing Al conductors with superior strength, high EC, and thermally stable precipitates, addressing the need for enhanced power transmission capabilities [2]. The addition of scandium (Sc) and zirconium (Zr) demonstrates considerable potential for developing Al alloys with high strength and improved thermal stability [17]. During the aging of supersaturated solid solutions in Sc- and Zr-containing Al alloys, nanoscale precipitates such as Al3Sc, Al3Zr, or core–shell Al3(Sc1−xZrx), with the metastable L12 structure, are formed [17–18]. These coherent precipitates exhibit strong interactions with the α-Al matrix, significantly enhancing mechanical strength at both ambient and elevated temperatures [19–22]. The ambient-temperature strength is generally attributed to mechanisms such as precipitate shearing, dislocation looping (Orowan bowing), or a combination of both [23]. At elevated temperatures, Sc- and Zr-containing precipitates effectively pin grain boundaries through the Zener pinning effect, inhibiting grain boundary migration and recrystallization, thus enhancing resistance to grain structure changes [24–26].