Fabrication of High-strength, High-toughness Nanostructured Al Alloys

Xtalic employs a novel reverse-pulse electrochemical deposition process to create nanostructured Aluminum alloys (nano-Al) with strengths more than twice traditional aluminum alloys, while retaining >8% elongation.  Our innovation is founded in creating thermodynamically stable nanostructures that impart dramatic improvements in properties such as strength, wear and ductility.  While nanocrystalline metals are known to exhibit high strength, typical nanostructures are thermodynamically unstable due to the large volume fraction of high-energy interfaces.  Grain coarsening occurs quickly in service leading to a rapid degradation of the enhanced properties.  A unique competency of our technology is that it focuses on creating thermodynamically stabilized nanocrystalline alloys.  When properly alloyed into Al, Mn favors disordered sites such as grain boundaries and secondary phases.  Since these disordered regions are energetically favored, they thermodynamically stabilize nanostructures against grain coarsening.  In fact, the Al-Mn alloy system exhibits tailorable grain sizes that span multiple orders of magnitude from micrometers down to nanometers.  The significant increase in alloy strength (while retaining ductility) with decreasing grain size, provides revolutionary, rather than evolutionary, improvement in Al properties.  Xtalic's nano-Al alloys are synthesized using electrolytic means similar to common commercial electroplating (coatings) and electroforming (bulk materials) processes.   By developing bath chemistry that permits the fabrication of thick free-standing samples, uniaxial tensile tests were performed.  High strengths above ~600MPa and ductility above ~8% were reproducibly obtained.  The enhanced strength is attributed to the Hall-Petch effect.  Analysis of fracture surfaces reveals evidence of ductile fracture, such as dimples and knife edges. Plasticity in these nanostructured alloys is attributed to dislocation activity.  Overall, it has been demonstrated that these new nano-Al alloys have the potential to replace steels due to the unique combination of high specific strength and ductility.