A lightweight zero thermal expansion magnesium alloy

Thermal expansion is an intrinsic property of metals and alloys, posing a critical challenge for achieving dimensional stability in lightweight systems where low atomic mass enhances lattice vibrations. Here, we present a strain recovery compensation strategy that achieves three orders of magnitude reduction in thermally induced volume change, enabling zero thermal expansion (ZTE) in a rare-earth magnesium alloy containing 1.2 vol.% Al-stabilized MnCoGe particles. The coefficient of thermal expansion is reduced from 28 × 10⁻⁶ °C⁻¹ to 0.02 × 10⁻⁶ °C⁻¹ over 25-150 °C-the highest thermal stability reported for any alloy. This alloy also retains high compressive strength (424 MPa), ductility (12%), and ultralow density (1.93 g/cm³). The ZTE behavior arises from sustained compressive strain, maintained by reversible martensitic transformation of the embedded particles. Beyond realizing a dimensional stable lightweight alloy, this work establishes a generalizable principle for achieving thermal dimensional stability in metals via recoverable strain.