Hot Extrusion Temperature Tunes Strength, Corrosion and Heat Flow in Low Rare-Earth Magnesium Alloy

Magnesium alloys have long promised to lighten cars, aircraft and electronic devices, but the lightest of all structural metals has always demanded a difficult bargain. Push a magnesium alloy to be strong and it usually corrodes faster and conducts heat poorly; make it conductive and corrosion-resistant and it tends to give up strength. A research team led by Yuzhao Xu and Xian Luo of the Zhejiang Business Technology Institute, working with colleagues at the University of Science and Technology Beijing, now reports in the Journal of Materials Science that much of this trade-off can be negotiated with a single, deceptively simple processing knob: the temperature of hot extrusion. Their alloy of choice contains only about two weight percent gadolinium and two weight percent zinc, a deliberately lean, low rare-earth composition designed to keep costs down in a materials class often criticized for its expensive alloying additions.

The researchers fabricated the Mg–2Gd–2Zn alloy by hot extrusion at three temperatures: 280, 320 and 360 degrees Celsius. Extrusion, in which a heated billet is forced through a die, does far more than shape the metal. It plastically deforms the crystal lattice, fragments and reorganizes grains, dissolves and reprecipitates secondary phases, and generates dense tangles of dislocations, the line defects that store deformation energy inside crystals. Each of these microstructural features feeds directly into the properties an engineer cares about: how much stress the material can carry before yielding, how far it stretches before breaking, how quickly it dissolves in corrosive media, and how efficiently it conducts heat away from a hot spot. By holding composition constant and varying only temperature, the team isolated the processing variable with unusual clarity.

The microstructures that emerged fell into two distinct regimes. Alloys extruded at the lower temperatures of 280 and 320 degrees Celsius developed what metallurgists call a bimodal structure, a patchwork of coarse-grained regions interwoven with fine-grained ones. Bimodal microstructures are prized because they mimic a composite: fine grains impede dislocation motion and raise yield strength, while coarse grains accommodate plastic strain and preserve ductility. When the extrusion temperature climbed to 360 degrees Celsius, the picture changed. Grain growth and dynamic recrystallization, the process by which new strain-free grains nucleate and grow during hot deformation, were both promoted, while the dislocation density and the intensity of the deformation texture declined. The material essentially relaxed, trading stored deformation energy for a more equilibrated, coarser grain structure.

The consequences for strength were dramatic, and in the opposite direction to what a casual reader might hope. Tensile yield strength fell from 338.2 megapascals in the cooler-extruded condition to 214.7 megapascals at the highest extrusion temperature, a loss of more than 120 megapascals. The authors attribute the high yield strength of the low-temperature material to a synergistic combination of strengthening mechanisms: fine grains that block dislocation slip through the Hall–Petch relationship, nanoscale precipitates that pin moving dislocations, and a high density of dislocations that tangle and stress one another. Remove any one of these and the yield strength suffers. At 360 degrees Celsius, coarser grains, reduced dislocation density and weakened texture combined to soften the alloy considerably.

Yet the same change that sapped strength delivered a remarkable gift in ductility. Total elongation before failure rose from 8.5 percent to 24.7 percent as extrusion temperature increased, nearly tripling the material’s formability. This is the classic strength–ductility see-saw in magnesium, but the magnitude of the swing, achieved with nothing more than a temperature change on an inexpensive, low-alloyed material, is what makes the result noteworthy. A component designer could, in principle, select an extrusion temperature to position the alloy anywhere along this spectrum: a stiff, strong condition for load-bearing brackets or a soft, ductile condition for parts requiring extensive subsequent forming.

Corrosion, the Achilles heel of magnesium, also responded favorably to higher extrusion temperatures. The corrosion rate dropped from 3.32 to 2.35 milligrams per square centimeter per day as the extrusion temperature rose from 320 to 360 degrees Celsius. The team traced this improvement to the microstructural evolution itself. The lower dislocation density and reduced texture intensity at high temperature promoted the formation of a more compact and uniform corrosion product film on the surface. Such a film acts as a barrier between reactive magnesium and the environment, suppressing the localized attack, such as pitting and galvanic corrosion at microstructural inhomogeneities, that typically consumes magnesium components. In other words, the more relaxed, recrystallized microstructure corrodes not just more slowly but more evenly.

Thermal conductivity, a property increasingly demanded in heat-dissipating electronics housings and powertrain components, also improved modestly with temperature. Conductivity rose from 124.6 to 129.7 watts per meter-kelvin across the extrusion temperature range. The physics behind this trend is well understood: heat in metals is carried predominantly by conduction electrons and lattice vibrations, both of which are scattered by crystal defects. Dislocations, solute atoms in solution and fine grain boundaries all shorten the mean free path of these carriers. As higher extrusion temperatures reduced dislocation density and allowed solute to precipitate out of the magnesium matrix, scattering diminished and heat flowed more freely. The fact that this gain in conductivity accompanied a gain in corrosion resistance, rather than coming at its expense, is a genuinely useful coincidence for practical alloy design.

The broader significance of the work lies in its economics as much as its metallurgy. High-performance magnesium alloys in the aerospace and automotive literature frequently carry rare-earth contents of six, eight or even ten weight percent, often combining gadolinium, yttrium, neodymium and other costly elements. Rare-earth supply chains are geographically concentrated and price-volatile, so diluting the recipe while preserving performance is a strategic goal for the industry. The Mg–2Gd–2Zn composition studied here demonstrates that a lean, roughly four percent total alloying addition can still deliver yield strengths approaching 340 megapascals, elongation approaching 25 percent, respectable thermal conductivity above 120 watts per meter-kelvin and steadily improving corrosion resistance, all from a conventional hot extrusion route requiring no exotic equipment.

The study also adds to a growing body of evidence that bimodal and heterogeneous microstructures offer a route around the strength–ductility dilemma that has constrained magnesium for decades. Recent work cited by the authors, including studies of heterogeneous structures in magnesium alloys and low-temperature extrusion of dilute Mg–Zn–Ce and Mg–Sm systems, points to the same underlying principle: controlling not just how big the grains are, but how differently sized grains coexist within one material, lets engineers combine properties that single-scale microstructures force them to trade away. The present study extends that principle to the coupled optimization of corrosion and thermal conductivity, showing that a bimodal structure optimized for strength can coexist with acceptable, and tunable, environmental and thermal performance.

For now, the practical recipe reads like a set of dial settings rather than a finished product. Extrude near 280 to 320 degrees Celsius when strength matters most; push toward 360 degrees Celsius when ductility, corrosion resistance and heat dissipation dominate the design brief. What the Ningbo and Beijing team has shown is that these settings act coherently on every property simultaneously, through one consistent set of microstructural levers: grain size, dislocation density, recrystallization state and texture. As magnesium competes with aluminum and increasingly with engineered polymers for lightweight applications from electric vehicle battery enclosures to laptop chassis, that kind of predictable, process-based control, achieved without expensive rare-earth loading, may prove to be the decisive advantage that finally moves wrought magnesium alloys from laboratory curiosities into mass-produced components.

Subject of Research: Effect of extrusion temperature on the microstructure, mechanical properties, corrosion behavior and thermal conductivity of a low rare-earth Mg–Gd–Zn magnesium alloy

Article Title: Investigation on the microstructure evolution, mechanical properties and corrosion behavior, thermal conductivity of low rare-earth containing Mg–Gd–Zn alloy: effect of extrusion temperatures

Article References: Xu, Y., Luo, X., Wang, G., & Hu, L. (2026). Investigation on the microstructure evolution, mechanical properties and corrosion behavior, thermal conductivity of low rare-earth containing Mg–Gd–Zn alloy: effect of extrusion temperatures. Journal of Materials Science. https://doi.org/10.1007/s10853-026-13905-3

Image Credits: AI Generated

DOI: 10.1007/s10853-026-13905-3

Keywords: magnesium alloys, Mg–Gd–Zn, hot extrusion, dynamic recrystallization, bimodal microstructure, yield strength, ductility, corrosion resistance, thermal conductivity, rare-earth elements, grain refinement, materials science